Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1506875 > unrolled thread

[RFC 0/8] Define coherent device memory node

Back to article view | Back to linux.kernel

Contents

  [RFC 0/8] Define coherent device memory node Anshuman Khandual <khandual@linux.vnet.ibm.com> - 2016-10-24 06:40 +0200
    [RFC 3/8] mm: Isolate coherent device memory nodes from HugeTLB allocation paths Anshuman Khandual <khandual@linux.vnet.ibm.com> - 2016-10-24 06:40 +0200
      Re: [RFC 3/8] mm: Isolate coherent device memory nodes from HugeTLB  allocation paths Dave Hansen <dave.hansen@intel.com> - 2016-10-24 19:20 +0200
        Re: [RFC 3/8] mm: Isolate coherent device memory nodes from HugeTLB allocation paths "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com> - 2016-10-25 06:20 +0200
          Re: [RFC 3/8] mm: Isolate coherent device memory nodes from HugeTLB  allocation paths Balbir Singh <bsingharora@gmail.com> - 2016-10-25 09:20 +0200
            Re: [RFC 3/8] mm: Isolate coherent device memory nodes from HugeTLB  allocation paths Balbir Singh <bsingharora@gmail.com> - 2016-10-25 09:30 +0200
    [RFC 7/8] mm: Add a new migration function migrate_virtual_range() Anshuman Khandual <khandual@linux.vnet.ibm.com> - 2016-10-24 06:40 +0200
    [DEBUG 06/10] mm: Export definition of 'zone_names' array through mmzone.h Anshuman Khandual <khandual@linux.vnet.ibm.com> - 2016-10-24 06:50 +0200
    [DEBUG 00/10] Test and debug patches for coherent device memory Anshuman Khandual <khandual@linux.vnet.ibm.com> - 2016-10-24 06:50 +0200
      [DEBUG 02/10] powerpc/mm: Create numa nodes for hotplug memory Anshuman Khandual <khandual@linux.vnet.ibm.com> - 2016-10-24 06:50 +0200
      [DEBUG 03/10] powerpc/mm: Allow memory hotplug into a memory less node Anshuman Khandual <khandual@linux.vnet.ibm.com> - 2016-10-24 06:50 +0200
      [DEBUG 08/10] powerpc: Enable CONFIG_MOVABLE_NODE for PPC64 platform Anshuman Khandual <khandual@linux.vnet.ibm.com> - 2016-10-24 06:50 +0200
      [DEBUG 01/10] dt-bindings: Add doc for ibm,hotplug-aperture Anshuman Khandual <khandual@linux.vnet.ibm.com> - 2016-10-24 06:50 +0200
      [DEBUG 05/10] powerpc/mm: Identify isolation seeking coherent memory nodes during boot Anshuman Khandual <khandual@linux.vnet.ibm.com> - 2016-10-24 06:50 +0200
      [DEBUG 10/10] test: Add a script to perform random VMA migrations across nodes Anshuman Khandual <khandual@linux.vnet.ibm.com> - 2016-10-24 06:50 +0200
      [DEBUG 07/10] mm: Add debugfs interface to dump each node's zonelist information Anshuman Khandual <khandual@linux.vnet.ibm.com> - 2016-10-24 06:50 +0200
      [DEBUG 04/10] mm: Enable CONFIG_MOVABLE_NODE on powerpc Anshuman Khandual <khandual@linux.vnet.ibm.com> - 2016-10-24 06:50 +0200
      [DEBUG 09/10] drivers: Add two drivers for coherent device memory tests Anshuman Khandual <khandual@linux.vnet.ibm.com> - 2016-10-24 06:50 +0200
    Re: [RFC 0/8] Define coherent device memory node Jerome Glisse <j.glisse@gmail.com> - 2016-10-24 19:10 +0200
      Re: [RFC 0/8] Define coherent device memory node "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com> - 2016-10-25 06:30 +0200
        Re: [RFC 0/8] Define coherent device memory node Jerome Glisse <j.glisse@gmail.com> - 2016-10-25 17:20 +0200
          Re: [RFC 0/8] Define coherent device memory node "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com> - 2016-10-26 13:10 +0200
            Re: [RFC 0/8] Define coherent device memory node Jerome Glisse <j.glisse@gmail.com> - 2016-10-26 18:10 +0200
      Re: [RFC 0/8] Define coherent device memory node "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com> - 2016-10-25 07:10 +0200
        Re: [RFC 0/8] Define coherent device memory node Jerome Glisse <j.glisse@gmail.com> - 2016-10-25 17:40 +0200
          Re: [RFC 0/8] Define coherent device memory node "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com> - 2016-10-25 19:40 +0200
            Re: [RFC 0/8] Define coherent device memory node Jerome Glisse <j.glisse@gmail.com> - 2016-10-25 21:00 +0200
              Re: [RFC 0/8] Define coherent device memory node Anshuman Khandual <khandual@linux.vnet.ibm.com> - 2016-10-26 13:20 +0200
                Re: [RFC 0/8] Define coherent device memory node Jerome Glisse <j.glisse@gmail.com> - 2016-10-26 18:10 +0200
              Re: [RFC 0/8] Define coherent device memory node Anshuman Khandual <khandual@linux.vnet.ibm.com> - 2016-10-26 15:00 +0200
                Re: [RFC 0/8] Define coherent device memory node Jerome Glisse <j.glisse@gmail.com> - 2016-10-26 18:30 +0200
      Re: [RFC 0/8] Define coherent device memory node Balbir Singh <bsingharora@gmail.com> - 2016-10-25 14:10 +0200
        Re: [RFC 0/8] Define coherent device memory node Jerome Glisse <j.glisse@gmail.com> - 2016-10-25 17:30 +0200
    Re: [RFC 0/8] Define coherent device memory node Dave Hansen <dave.hansen@intel.com> - 2016-10-24 20:10 +0200
      Re: [RFC 0/8] Define coherent device memory node David Nellans <dnellans@nvidia.com> - 2016-10-24 20:40 +0200
        Re: [RFC 0/8] Define coherent device memory node Dave Hansen <dave.hansen@intel.com> - 2016-10-24 21:40 +0200

Page 2 of 2 — ← Prev page 1 [2]

#1508376

On Tue, Oct 25, 2016 at 09:56:35AM +0530, Aneesh Kumar K.V wrote:
> Jerome Glisse <j.glisse@gmail.com> writes:
> 
> > On Mon, Oct 24, 2016 at 10:01:49AM +0530, Anshuman Khandual wrote:
> >
> >> [...]
> >
> >> 	Core kernel memory features like reclamation, evictions etc. might
> >> need to be restricted or modified on the coherent device memory node as
> >> they can be performance limiting. The RFC does not propose anything on this
> >> yet but it can be looked into later on. For now it just disables Auto NUMA
> >> for any VMA which has coherent device memory.
> >> 
> >> 	Seamless integration of coherent device memory with system memory
> >> will enable various other features, some of which can be listed as follows.
> >> 
> >> 	a. Seamless migrations between system RAM and the coherent memory
> >> 	b. Will have asynchronous and high throughput migrations
> >> 	c. Be able to allocate huge order pages from these memory regions
> >> 	d. Restrict allocations to a large extent to the tasks using the
> >> 	   device for workload acceleration
> >> 
> >> 	Before concluding, will look into the reasons why the existing
> >> solutions don't work. There are two basic requirements which have to be
> >> satisfies before the coherent device memory can be integrated with core
> >> kernel seamlessly.
> >> 
> >> 	a. PFN must have struct page
> >> 	b. Struct page must able to be inside standard LRU lists
> >> 
> >> 	The above two basic requirements discard the existing method of
> >> device memory representation approaches like these which then requires the
> >> need of creating a new framework.
> >
> > I do not believe the LRU list is a hard requirement, yes when faulting in
> > a page inside the page cache it assumes it needs to be added to lru list.
> > But i think this can easily be work around.
> >
> > In HMM i am using ZONE_DEVICE and because memory is not accessible from CPU
> > (not everyone is bless with decent system bus like CAPI, CCIX, Gen-Z, ...)
> > so in my case a file back page must always be spawn first from a regular
> > page and once read from disk then i can migrate to GPU page.
> >
> > So if you accept this intermediary step you can easily use ZONE_DEVICE for
> > device memory. This way no lru, no complex dance to make the memory out of
> > reach from regular memory allocator.
> 
> One of the reason to look at this as a NUMA node is to allow things like
> over-commit of coherent device memory. The pages backing CDM being part of
> lru and considering the coherent device as a numa node makes that really
> simpler (we can run kswapd for that node).

I am not convince that kswapd is what you want for overcommit, for HMM i leave
overcommit to device driver and they seem quite happy about handling that
themself. Only the device driver have enough information on what is worth
evicting or what need to be evicted.
 
> > I think we would have much to gain if we pool our effort on a single common
> > solution for device memory. In my case the device memory is not accessible
> > by the CPU (because PCIE restrictions), in your case it is. Thus the only
> > difference is that in my case it can not be map inside the CPU page table
> > while in yours it can.
> 
> IMHO, we should be able to share the HMM migration approach. We
> definitely won't need the mirror page table part. That is one of the
> reson I requested HMM mirror page table to be a seperate patchset.

They will need to share one thing, that is hmm_pfn_t which is a special pfn
type in which i store HMM and migrate specific flag for migration. Because
i can not use the struct list_head lru of struct page i have to do migration
using array of pfn and i need to keep some flags per page during migration.

So i share the same type hmm_pfn_t btw mirror and migrate code. But that's
pretty small and it can be factor out of HMM, i can also just use pfn_t and
add flag i need their.
 
> 
> >
> >> 
> >> (1) Traditional ioremap
> >> 
> >> 	a. Memory is mapped into kernel (linear and virtual) and user space
> >> 	b. These PFNs do not have struct pages associated with it
> >> 	c. These special PFNs are marked with special flags inside the PTE
> >> 	d. Cannot participate in core VM functions much because of this
> >> 	e. Cannot do easy user space migrations
> >> 
> >> (2) Zone ZONE_DEVICE
> >> 
> >> 	a. Memory is mapped into kernel and user space
> >> 	b. PFNs do have struct pages associated with it
> >> 	c. These struct pages are allocated inside it's own memory range
> >> 	d. Unfortunately the struct page's union containing LRU has been
> >> 	   used for struct dev_pagemap pointer
> >> 	e. Hence it cannot be part of any LRU (like Page cache)
> >> 	f. Hence file cached mapping cannot reside on these PFNs
> >> 	g. Cannot do easy migrations
> >> 
> >> 	I had also explored non LRU representation of this coherent device
> >> memory where the integration with system RAM in the core VM is limited only
> >> to the following functions. Not being inside LRU is definitely going to
> >> reduce the scope of tight integration with system RAM.
> >> 
> >> (1) Migration support between system RAM and coherent memory
> >> (2) Migration support between various coherent memory nodes
> >> (3) Isolation of the coherent memory
> >> (4) Mapping the coherent memory into user space through driver's
> >>     struct vm_operations
> >> (5) HW poisoning of the coherent memory
> >> 
> >> 	Allocating the entire memory of the coherent device node right
> >> after hot plug into ZONE_MOVABLE (where the memory is already inside the
> >> buddy system) will still expose a time window where other user space
> >> allocations can come into the coherent device memory node and prevent the
> >> intended isolation. So traditional hot plug is not the solution. Hence
> >> started looking into CMA based non LRU solution but then hit the following
> >> roadblocks.
> >> 
> >> (1) CMA does not support hot plugging of new memory node
> >> 	a. CMA area needs to be marked during boot before buddy is
> >> 	   initialized
> >> 	b. cma_alloc()/cma_release() can happen on the marked area
> >> 	c. Should be able to mark the CMA areas just after memory hot plug
> >> 	d. cma_alloc()/cma_release() can happen later after the hot plug
> >> 	e. This is not currently supported right now
> >> 
> >> (2) Mapped non LRU migration of pages
> >> 	a. Recent work from Michan Kim makes non LRU page migratable
> >> 	b. But it still does not support migration of mapped non LRU pages
> >> 	c. With non LRU CMA reserved, again there are some additional
> >> 	   challenges
> >> 
> >> 	With hot pluggable CMA and non LRU mapped migration support there
> >> may be an alternate approach to represent coherent device memory. Please
> >> do review this RFC proposal and let me know your comments or suggestions.
> >> Thank you.
> >
> > You can take a look at hmm-v13 if you want to see how i do non LRU page
> > migration. While i put most of the migration code inside hmm_migrate.c it
> > could easily be move to migrate.c without hmm_ prefix.
> >
> > There is 2 missing piece with existing migrate code. First is to put memory
> > allocation for destination under control of who call the migrate code. Second
> > is to allow offloading the copy operation to device (ie not use the CPU to
> > copy data).
> >
> > I believe same requirement also make sense for platform you are targeting.
> > Thus same code can be use.
> >
> > hmm-v13 https://cgit.freedesktop.org/~glisse/linux/log/?h=hmm-v13
> >
> > I haven't posted this patchset yet because we are doing some modifications
> > to the device driver API to accomodate some new features. But the ZONE_DEVICE
> > changes and the overall migration code will stay the same more or less (i have
> > patches that move it to migrate.c and share more code with existing migrate
> > code).
> >
> > If you think i missed anything about lru and page cache please point it to
> > me. Because when i audited code for that i didn't see any road block with
> > the few fs i was looking at (ext4, xfs and core page cache code).
> 
> I looked at the hmm-v13 w.r.t migration and I guess some form of device
> callback/acceleration during migration is something we should definitely
> have. I still haven't figured out how non addressable and coherent device
> memory can fit together there. I was waiting for the page cache
> migration support to be pushed to the repository before I start looking
> at this closely.
> 

The page cache migration does not touch the migrate code path. My issue with
page cache is writeback. The only difference with existing migrate code is
refcount check for ZONE_DEVICE page. Everything else is the same.

For writeback i need to use a bounce page so basicly i am trying to hook myself
along the ISA bounce infrastructure for bio and i think it is the easiest path
to solve this in my case.

In your case where block device can also access the device memory you don't
even need to use bounce page for writeback.

Cheers,
Jérôme

[toc] | [prev] | [next] | [standalone]

#1509062

Jerome Glisse <j.glisse@gmail.com> writes:

> On Tue, Oct 25, 2016 at 09:56:35AM +0530, Aneesh Kumar K.V wrote:
>> Jerome Glisse <j.glisse@gmail.com> writes:
>> 
>> > On Mon, Oct 24, 2016 at 10:01:49AM +0530, Anshuman Khandual wrote:
>> >
>> I looked at the hmm-v13 w.r.t migration and I guess some form of device
>> callback/acceleration during migration is something we should definitely
>> have. I still haven't figured out how non addressable and coherent device
>> memory can fit together there. I was waiting for the page cache
>> migration support to be pushed to the repository before I start looking
>> at this closely.
>> 
>
> The page cache migration does not touch the migrate code path. My issue with
> page cache is writeback. The only difference with existing migrate code is
> refcount check for ZONE_DEVICE page. Everything else is the same.

What about the radix tree ? does file system migrate_page callback handle
replacing normal page with ZONE_DEVICE page/exceptional entries ?

>
> For writeback i need to use a bounce page so basicly i am trying to hook myself
> along the ISA bounce infrastructure for bio and i think it is the easiest path
> to solve this in my case.
>
> In your case where block device can also access the device memory you don't
> even need to use bounce page for writeback.
>

-aneesh

[toc] | [prev] | [next] | [standalone]

#1509561

On Wed, Oct 26, 2016 at 04:39:19PM +0530, Aneesh Kumar K.V wrote:
> Jerome Glisse <j.glisse@gmail.com> writes:
> 
> > On Tue, Oct 25, 2016 at 09:56:35AM +0530, Aneesh Kumar K.V wrote:
> >> Jerome Glisse <j.glisse@gmail.com> writes:
> >> 
> >> > On Mon, Oct 24, 2016 at 10:01:49AM +0530, Anshuman Khandual wrote:
> >> >
> >> I looked at the hmm-v13 w.r.t migration and I guess some form of device
> >> callback/acceleration during migration is something we should definitely
> >> have. I still haven't figured out how non addressable and coherent device
> >> memory can fit together there. I was waiting for the page cache
> >> migration support to be pushed to the repository before I start looking
> >> at this closely.
> >> 
> >
> > The page cache migration does not touch the migrate code path. My issue with
> > page cache is writeback. The only difference with existing migrate code is
> > refcount check for ZONE_DEVICE page. Everything else is the same.
> 
> What about the radix tree ? does file system migrate_page callback handle
> replacing normal page with ZONE_DEVICE page/exceptional entries ?
> 

It use the exact same existing code (from mm/migrate.c) so yes the radix tree
is updated and buffer_head are migrated.

Jérôme

[toc] | [prev] | [next] | [standalone]

#1507971

Jerome Glisse <j.glisse@gmail.com> writes:

> On Mon, Oct 24, 2016 at 10:01:49AM +0530, Anshuman Khandual wrote:
>
>> [...]
>
>> 	Core kernel memory features like reclamation, evictions etc. might
>> need to be restricted or modified on the coherent device memory node as
>> they can be performance limiting. The RFC does not propose anything on this
>> yet but it can be looked into later on. For now it just disables Auto NUMA
>> for any VMA which has coherent device memory.
>> 
>> 	Seamless integration of coherent device memory with system memory
>> will enable various other features, some of which can be listed as follows.
>> 
>> 	a. Seamless migrations between system RAM and the coherent memory
>> 	b. Will have asynchronous and high throughput migrations
>> 	c. Be able to allocate huge order pages from these memory regions
>> 	d. Restrict allocations to a large extent to the tasks using the
>> 	   device for workload acceleration
>> 
>> 	Before concluding, will look into the reasons why the existing
>> solutions don't work. There are two basic requirements which have to be
>> satisfies before the coherent device memory can be integrated with core
>> kernel seamlessly.
>> 
>> 	a. PFN must have struct page
>> 	b. Struct page must able to be inside standard LRU lists
>> 
>> 	The above two basic requirements discard the existing method of
>> device memory representation approaches like these which then requires the
>> need of creating a new framework.
>
> I do not believe the LRU list is a hard requirement, yes when faulting in
> a page inside the page cache it assumes it needs to be added to lru list.
> But i think this can easily be work around.
>
> In HMM i am using ZONE_DEVICE and because memory is not accessible from CPU
> (not everyone is bless with decent system bus like CAPI, CCIX, Gen-Z, ...)
> so in my case a file back page must always be spawn first from a regular
> page and once read from disk then i can migrate to GPU page.
>
> So if you accept this intermediary step you can easily use ZONE_DEVICE for
> device memory. This way no lru, no complex dance to make the memory out of
> reach from regular memory allocator.
>
> I think we would have much to gain if we pool our effort on a single common
> solution for device memory. In my case the device memory is not accessible
> by the CPU (because PCIE restrictions), in your case it is. Thus the only
> difference is that in my case it can not be map inside the CPU page table
> while in yours it can.
>
>> 
>> (1) Traditional ioremap
>> 
>> 	a. Memory is mapped into kernel (linear and virtual) and user space
>> 	b. These PFNs do not have struct pages associated with it
>> 	c. These special PFNs are marked with special flags inside the PTE
>> 	d. Cannot participate in core VM functions much because of this
>> 	e. Cannot do easy user space migrations
>> 
>> (2) Zone ZONE_DEVICE
>> 
>> 	a. Memory is mapped into kernel and user space
>> 	b. PFNs do have struct pages associated with it
>> 	c. These struct pages are allocated inside it's own memory range
>> 	d. Unfortunately the struct page's union containing LRU has been
>> 	   used for struct dev_pagemap pointer
>> 	e. Hence it cannot be part of any LRU (like Page cache)
>> 	f. Hence file cached mapping cannot reside on these PFNs
>> 	g. Cannot do easy migrations
>> 
>> 	I had also explored non LRU representation of this coherent device
>> memory where the integration with system RAM in the core VM is limited only
>> to the following functions. Not being inside LRU is definitely going to
>> reduce the scope of tight integration with system RAM.
>> 
>> (1) Migration support between system RAM and coherent memory
>> (2) Migration support between various coherent memory nodes
>> (3) Isolation of the coherent memory
>> (4) Mapping the coherent memory into user space through driver's
>>     struct vm_operations
>> (5) HW poisoning of the coherent memory
>> 
>> 	Allocating the entire memory of the coherent device node right
>> after hot plug into ZONE_MOVABLE (where the memory is already inside the
>> buddy system) will still expose a time window where other user space
>> allocations can come into the coherent device memory node and prevent the
>> intended isolation. So traditional hot plug is not the solution. Hence
>> started looking into CMA based non LRU solution but then hit the following
>> roadblocks.
>> 
>> (1) CMA does not support hot plugging of new memory node
>> 	a. CMA area needs to be marked during boot before buddy is
>> 	   initialized
>> 	b. cma_alloc()/cma_release() can happen on the marked area
>> 	c. Should be able to mark the CMA areas just after memory hot plug
>> 	d. cma_alloc()/cma_release() can happen later after the hot plug
>> 	e. This is not currently supported right now
>> 
>> (2) Mapped non LRU migration of pages
>> 	a. Recent work from Michan Kim makes non LRU page migratable
>> 	b. But it still does not support migration of mapped non LRU pages
>> 	c. With non LRU CMA reserved, again there are some additional
>> 	   challenges
>> 
>> 	With hot pluggable CMA and non LRU mapped migration support there
>> may be an alternate approach to represent coherent device memory. Please
>> do review this RFC proposal and let me know your comments or suggestions.
>> Thank you.
>
> You can take a look at hmm-v13 if you want to see how i do non LRU page
> migration. While i put most of the migration code inside hmm_migrate.c it
> could easily be move to migrate.c without hmm_ prefix.
>
> There is 2 missing piece with existing migrate code. First is to put memory
> allocation for destination under control of who call the migrate code. Second
> is to allow offloading the copy operation to device (ie not use the CPU to
> copy data).
>
> I believe same requirement also make sense for platform you are targeting.
> Thus same code can be use.
>
> hmm-v13 https://cgit.freedesktop.org/~glisse/linux/log/?h=hmm-v13
>
> I haven't posted this patchset yet because we are doing some modifications
> to the device driver API to accomodate some new features. But the ZONE_DEVICE
> changes and the overall migration code will stay the same more or less (i have
> patches that move it to migrate.c and share more code with existing migrate
> code).
>
> If you think i missed anything about lru and page cache please point it to
> me. Because when i audited code for that i didn't see any road block with
> the few fs i was looking at (ext4, xfs and core page cache code).
>

The other restriction around ZONE_DEVICE is, it is not a managed zone.
That prevents any direct allocation from coherent device by application.
ie, we would like to force allocation from coherent device using
interface like mbind(MPOL_BIND..) . Is that possible with ZONE_DEVICE ?

-aneeesh

[toc] | [prev] | [next] | [standalone]

#1508383

On Tue, Oct 25, 2016 at 10:29:38AM +0530, Aneesh Kumar K.V wrote:
> Jerome Glisse <j.glisse@gmail.com> writes:
> > On Mon, Oct 24, 2016 at 10:01:49AM +0530, Anshuman Khandual wrote:

[...]

> > You can take a look at hmm-v13 if you want to see how i do non LRU page
> > migration. While i put most of the migration code inside hmm_migrate.c it
> > could easily be move to migrate.c without hmm_ prefix.
> >
> > There is 2 missing piece with existing migrate code. First is to put memory
> > allocation for destination under control of who call the migrate code. Second
> > is to allow offloading the copy operation to device (ie not use the CPU to
> > copy data).
> >
> > I believe same requirement also make sense for platform you are targeting.
> > Thus same code can be use.
> >
> > hmm-v13 https://cgit.freedesktop.org/~glisse/linux/log/?h=hmm-v13
> >
> > I haven't posted this patchset yet because we are doing some modifications
> > to the device driver API to accomodate some new features. But the ZONE_DEVICE
> > changes and the overall migration code will stay the same more or less (i have
> > patches that move it to migrate.c and share more code with existing migrate
> > code).
> >
> > If you think i missed anything about lru and page cache please point it to
> > me. Because when i audited code for that i didn't see any road block with
> > the few fs i was looking at (ext4, xfs and core page cache code).
> >
> 
> The other restriction around ZONE_DEVICE is, it is not a managed zone.
> That prevents any direct allocation from coherent device by application.
> ie, we would like to force allocation from coherent device using
> interface like mbind(MPOL_BIND..) . Is that possible with ZONE_DEVICE ?
 
To achieve this we rely on device fault code path ie when device take a page fault
with help of HMM it will use existing memory if any for fault address but if CPU
page table is empty (and it is not file back vma because of readback) then device
can directly allocate device memory and HMM will update CPU page table to point to
newly allocated device memory.

So in fact i am not using existing kernel API to achieve this but the whole policy
of where to allocate and what to allocate is under device driver responsability and
device driver leverage its existing userspace API to get proper hint/direction from
the application.

Device memory is really a special case in my view, it only make sense to use it if
memory is actively access by device and only way device access memory is when it is
program to do so through the device driver API. There is nothing such as GPU threads
in the kernel and there is no way to spawn or move work thread to GPU. This are
specialize device and they require special per device API. So in my view using
existing kernel API such as mbind() is counter productive. You might have buggy
software that will mbind their memory to device and never use the device which
lead to device memory being wasted for a process that never use the device.

So my opinion is that you should not try to use existing kernel API to get policy
information from userspace but let the device driver gather such policy through its
own private API.

Cheers,
Jérôme

[toc] | [prev] | [next] | [standalone]

#1508503

Jerome Glisse <j.glisse@gmail.com> writes:

> On Tue, Oct 25, 2016 at 10:29:38AM +0530, Aneesh Kumar K.V wrote:
>> Jerome Glisse <j.glisse@gmail.com> writes:
>> > On Mon, Oct 24, 2016 at 10:01:49AM +0530, Anshuman Khandual wrote:
>
> [...]
>
>> > You can take a look at hmm-v13 if you want to see how i do non LRU page
>> > migration. While i put most of the migration code inside hmm_migrate.c it
>> > could easily be move to migrate.c without hmm_ prefix.
>> >
>> > There is 2 missing piece with existing migrate code. First is to put memory
>> > allocation for destination under control of who call the migrate code. Second
>> > is to allow offloading the copy operation to device (ie not use the CPU to
>> > copy data).
>> >
>> > I believe same requirement also make sense for platform you are targeting.
>> > Thus same code can be use.
>> >
>> > hmm-v13 https://cgit.freedesktop.org/~glisse/linux/log/?h=hmm-v13
>> >
>> > I haven't posted this patchset yet because we are doing some modifications
>> > to the device driver API to accomodate some new features. But the ZONE_DEVICE
>> > changes and the overall migration code will stay the same more or less (i have
>> > patches that move it to migrate.c and share more code with existing migrate
>> > code).
>> >
>> > If you think i missed anything about lru and page cache please point it to
>> > me. Because when i audited code for that i didn't see any road block with
>> > the few fs i was looking at (ext4, xfs and core page cache code).
>> >
>> 
>> The other restriction around ZONE_DEVICE is, it is not a managed zone.
>> That prevents any direct allocation from coherent device by application.
>> ie, we would like to force allocation from coherent device using
>> interface like mbind(MPOL_BIND..) . Is that possible with ZONE_DEVICE ?
>
> To achieve this we rely on device fault code path ie when device take a page fault
> with help of HMM it will use existing memory if any for fault address but if CPU
> page table is empty (and it is not file back vma because of readback) then device
> can directly allocate device memory and HMM will update CPU page table to point to
> newly allocated device memory.
>

That is ok if the device touch the page first. What if we want the
allocation touched first by cpu to come from GPU ?. Should we always
depend on GPU driver to migrate such pages later from system RAM to GPU
memory ?

-aneesh

[toc] | [prev] | [next] | [standalone]

#1508556

On Tue, Oct 25, 2016 at 11:01:08PM +0530, Aneesh Kumar K.V wrote:
> Jerome Glisse <j.glisse@gmail.com> writes:
> 
> > On Tue, Oct 25, 2016 at 10:29:38AM +0530, Aneesh Kumar K.V wrote:
> >> Jerome Glisse <j.glisse@gmail.com> writes:
> >> > On Mon, Oct 24, 2016 at 10:01:49AM +0530, Anshuman Khandual wrote:
> >
> > [...]
> >
> >> > You can take a look at hmm-v13 if you want to see how i do non LRU page
> >> > migration. While i put most of the migration code inside hmm_migrate.c it
> >> > could easily be move to migrate.c without hmm_ prefix.
> >> >
> >> > There is 2 missing piece with existing migrate code. First is to put memory
> >> > allocation for destination under control of who call the migrate code. Second
> >> > is to allow offloading the copy operation to device (ie not use the CPU to
> >> > copy data).
> >> >
> >> > I believe same requirement also make sense for platform you are targeting.
> >> > Thus same code can be use.
> >> >
> >> > hmm-v13 https://cgit.freedesktop.org/~glisse/linux/log/?h=hmm-v13
> >> >
> >> > I haven't posted this patchset yet because we are doing some modifications
> >> > to the device driver API to accomodate some new features. But the ZONE_DEVICE
> >> > changes and the overall migration code will stay the same more or less (i have
> >> > patches that move it to migrate.c and share more code with existing migrate
> >> > code).
> >> >
> >> > If you think i missed anything about lru and page cache please point it to
> >> > me. Because when i audited code for that i didn't see any road block with
> >> > the few fs i was looking at (ext4, xfs and core page cache code).
> >> >
> >> 
> >> The other restriction around ZONE_DEVICE is, it is not a managed zone.
> >> That prevents any direct allocation from coherent device by application.
> >> ie, we would like to force allocation from coherent device using
> >> interface like mbind(MPOL_BIND..) . Is that possible with ZONE_DEVICE ?
> >
> > To achieve this we rely on device fault code path ie when device take a page fault
> > with help of HMM it will use existing memory if any for fault address but if CPU
> > page table is empty (and it is not file back vma because of readback) then device
> > can directly allocate device memory and HMM will update CPU page table to point to
> > newly allocated device memory.
> >
> 
> That is ok if the device touch the page first. What if we want the
> allocation touched first by cpu to come from GPU ?. Should we always
> depend on GPU driver to migrate such pages later from system RAM to GPU
> memory ?
> 

I am not sure what kind of workload would rather have every first CPU access for
a range to use device memory. So no my code does not handle that and it is pointless
for it as CPU can not access device memory for me.

That said nothing forbid to add support for ZONE_DEVICE with mbind() like syscall.
Thought my personnal preference would still be to avoid use of such generic syscall
but have device driver set allocation policy through its own userspace API (device
driver could reuse internal of mbind() to achieve the end result).

I am not saying that eveything you want to do is doable now with HMM but, nothing
preclude achieving what you want to achieve using ZONE_DEVICE. I really don't think
any of the existing mm mechanism (kswapd, lru, numa, ...) are nice fit and can be reuse
with device memory.

Each device is so different from the other that i don't believe in a one API fit all.
The drm GPU subsystem of the kernel is a testimony of how little can be share when it
comes to GPU. The only common code is modesetting. Everything that deals with how to
use GPU to compute stuff is per device and most of the logic is in userspace. So i do
not see any commonality that could be abstracted at syscall level. I would rather let
device driver stack (kernel and userspace) take such decision and have the higher level
API (OpenCL, Cuda, C++17, ...) expose something that make sense for each of them.
Programmer target those high level API and they intend to use the mechanism each offer
to manage memory and memory placement. I would say forcing them to use a second linux
specific API to achieve the latter is wrong, at lest for now.

So in the end if the mbind() syscall is done by the userspace side of the device driver
then why not just having the device driver communicate this through its own kernel
API (which can be much more expressive than what standardize syscall offers). I would
rather avoid making change to any syscall for now.

If latter, down the road, once the userspace ecosystem stabilize, we see that there
is a good level at which we can abstract memory policy for enough devices then and
only then it would make sense to either introduce new syscall or grow/modify existing
one. Right now i fear we could only make bad decision that we would regret down the
road.

I think we can achieve memory device support with the minimum amount of changes to mm
code and existing mm mechanism. Using ZONE_DEVICE already make sure that such memory
is kept out of most mm mechanism and hence avoid all the changes you had to make for
CDM node. It just looks a better fit from my point of view. I think it is worth
considering for your use case too. I am sure folks writting the device driver would
rather share more code between platform with grown up bus system (CAPI, CCIX, ...)
vs platform with kid bus system (PCIE let's forget about PCI and ISA :))

Cheers,
Jérôme

[toc] | [prev] | [next] | [standalone]

#1509090

On 10/26/2016 12:22 AM, Jerome Glisse wrote:
> On Tue, Oct 25, 2016 at 11:01:08PM +0530, Aneesh Kumar K.V wrote:
>> Jerome Glisse <j.glisse@gmail.com> writes:
>>
>>> On Tue, Oct 25, 2016 at 10:29:38AM +0530, Aneesh Kumar K.V wrote:
>>>> Jerome Glisse <j.glisse@gmail.com> writes:
>>>>> On Mon, Oct 24, 2016 at 10:01:49AM +0530, Anshuman Khandual wrote:
>>>
>>> [...]
>>>
>>>>> You can take a look at hmm-v13 if you want to see how i do non LRU page
>>>>> migration. While i put most of the migration code inside hmm_migrate.c it
>>>>> could easily be move to migrate.c without hmm_ prefix.
>>>>>
>>>>> There is 2 missing piece with existing migrate code. First is to put memory
>>>>> allocation for destination under control of who call the migrate code. Second
>>>>> is to allow offloading the copy operation to device (ie not use the CPU to
>>>>> copy data).
>>>>>
>>>>> I believe same requirement also make sense for platform you are targeting.
>>>>> Thus same code can be use.
>>>>>
>>>>> hmm-v13 https://cgit.freedesktop.org/~glisse/linux/log/?h=hmm-v13
>>>>>
>>>>> I haven't posted this patchset yet because we are doing some modifications
>>>>> to the device driver API to accomodate some new features. But the ZONE_DEVICE
>>>>> changes and the overall migration code will stay the same more or less (i have
>>>>> patches that move it to migrate.c and share more code with existing migrate
>>>>> code).
>>>>>
>>>>> If you think i missed anything about lru and page cache please point it to
>>>>> me. Because when i audited code for that i didn't see any road block with
>>>>> the few fs i was looking at (ext4, xfs and core page cache code).
>>>>>
>>>>
>>>> The other restriction around ZONE_DEVICE is, it is not a managed zone.
>>>> That prevents any direct allocation from coherent device by application.
>>>> ie, we would like to force allocation from coherent device using
>>>> interface like mbind(MPOL_BIND..) . Is that possible with ZONE_DEVICE ?
>>>
>>> To achieve this we rely on device fault code path ie when device take a page fault
>>> with help of HMM it will use existing memory if any for fault address but if CPU
>>> page table is empty (and it is not file back vma because of readback) then device
>>> can directly allocate device memory and HMM will update CPU page table to point to
>>> newly allocated device memory.
>>>
>>
>> That is ok if the device touch the page first. What if we want the
>> allocation touched first by cpu to come from GPU ?. Should we always
>> depend on GPU driver to migrate such pages later from system RAM to GPU
>> memory ?
>>
> 
> I am not sure what kind of workload would rather have every first CPU access for
> a range to use device memory. So no my code does not handle that and it is pointless
> for it as CPU can not access device memory for me.
> 
> That said nothing forbid to add support for ZONE_DEVICE with mbind() like syscall.
> Thought my personnal preference would still be to avoid use of such generic syscall
> but have device driver set allocation policy through its own userspace API (device
> driver could reuse internal of mbind() to achieve the end result).
> 
> I am not saying that eveything you want to do is doable now with HMM but, nothing
> preclude achieving what you want to achieve using ZONE_DEVICE. I really don't think
> any of the existing mm mechanism (kswapd, lru, numa, ...) are nice fit and can be reuse
> with device memory.
> 
> Each device is so different from the other that i don't believe in a one API fit all.
> The drm GPU subsystem of the kernel is a testimony of how little can be share when it
> comes to GPU. The only common code is modesetting. Everything that deals with how to
> use GPU to compute stuff is per device and most of the logic is in userspace. So i do
> not see any commonality that could be abstracted at syscall level. I would rather let
> device driver stack (kernel and userspace) take such decision and have the higher level
> API (OpenCL, Cuda, C++17, ...) expose something that make sense for each of them.
> Programmer target those high level API and they intend to use the mechanism each offer
> to manage memory and memory placement. I would say forcing them to use a second linux
> specific API to achieve the latter is wrong, at lest for now.
> 
> So in the end if the mbind() syscall is done by the userspace side of the device driver
> then why not just having the device driver communicate this through its own kernel
> API (which can be much more expressive than what standardize syscall offers). I would
> rather avoid making change to any syscall for now.
> 
> If latter, down the road, once the userspace ecosystem stabilize, we see that there
> is a good level at which we can abstract memory policy for enough devices then and
> only then it would make sense to either introduce new syscall or grow/modify existing
> one. Right now i fear we could only make bad decision that we would regret down the
> road.
> 
> I think we can achieve memory device support with the minimum amount of changes to mm
> code and existing mm mechanism. Using ZONE_DEVICE already make sure that such memory
> is kept out of most mm mechanism and hence avoid all the changes you had to make for
> CDM node. It just looks a better fit from my point of view. I think it is worth
> considering for your use case too. I am sure folks writting the device driver would
> rather share more code between platform with grown up bus system (CAPI, CCIX, ...)
> vs platform with kid bus system (PCIE let's forget about PCI and ISA :))

Because of coherent access between the CPU and the device, the intention is to use
the same buffer (VMA) accessed between CPU and device interchangeably through out
the run time of the application depending upon which side is accessing more and
how much of performance benefit it will provide after the migration. Now driver
managed memory is non LRU (whether we use ZONE_DEVICE or not) and we had issues
migrating non LRU pages mapped in user space. I am not sure whether Minchan had
changed the basic non LRU migration enablement code to support mapped non LRU
pages well. So in that case how we are going to migrate back and forth between
system RAM and device memory ?

[toc] | [prev] | [next] | [standalone]

#1509560

On Wed, Oct 26, 2016 at 04:43:10PM +0530, Anshuman Khandual wrote:
> On 10/26/2016 12:22 AM, Jerome Glisse wrote:
> > On Tue, Oct 25, 2016 at 11:01:08PM +0530, Aneesh Kumar K.V wrote:
> >> Jerome Glisse <j.glisse@gmail.com> writes:
> >>
> >>> On Tue, Oct 25, 2016 at 10:29:38AM +0530, Aneesh Kumar K.V wrote:
> >>>> Jerome Glisse <j.glisse@gmail.com> writes:
> >>>>> On Mon, Oct 24, 2016 at 10:01:49AM +0530, Anshuman Khandual wrote:
> >>>
> >>> [...]
> >>>
> >>>>> You can take a look at hmm-v13 if you want to see how i do non LRU page
> >>>>> migration. While i put most of the migration code inside hmm_migrate.c it
> >>>>> could easily be move to migrate.c without hmm_ prefix.
> >>>>>
> >>>>> There is 2 missing piece with existing migrate code. First is to put memory
> >>>>> allocation for destination under control of who call the migrate code. Second
> >>>>> is to allow offloading the copy operation to device (ie not use the CPU to
> >>>>> copy data).
> >>>>>
> >>>>> I believe same requirement also make sense for platform you are targeting.
> >>>>> Thus same code can be use.
> >>>>>
> >>>>> hmm-v13 https://cgit.freedesktop.org/~glisse/linux/log/?h=hmm-v13
> >>>>>
> >>>>> I haven't posted this patchset yet because we are doing some modifications
> >>>>> to the device driver API to accomodate some new features. But the ZONE_DEVICE
> >>>>> changes and the overall migration code will stay the same more or less (i have
> >>>>> patches that move it to migrate.c and share more code with existing migrate
> >>>>> code).
> >>>>>
> >>>>> If you think i missed anything about lru and page cache please point it to
> >>>>> me. Because when i audited code for that i didn't see any road block with
> >>>>> the few fs i was looking at (ext4, xfs and core page cache code).
> >>>>>
> >>>>
> >>>> The other restriction around ZONE_DEVICE is, it is not a managed zone.
> >>>> That prevents any direct allocation from coherent device by application.
> >>>> ie, we would like to force allocation from coherent device using
> >>>> interface like mbind(MPOL_BIND..) . Is that possible with ZONE_DEVICE ?
> >>>
> >>> To achieve this we rely on device fault code path ie when device take a page fault
> >>> with help of HMM it will use existing memory if any for fault address but if CPU
> >>> page table is empty (and it is not file back vma because of readback) then device
> >>> can directly allocate device memory and HMM will update CPU page table to point to
> >>> newly allocated device memory.
> >>>
> >>
> >> That is ok if the device touch the page first. What if we want the
> >> allocation touched first by cpu to come from GPU ?. Should we always
> >> depend on GPU driver to migrate such pages later from system RAM to GPU
> >> memory ?
> >>
> > 
> > I am not sure what kind of workload would rather have every first CPU access for
> > a range to use device memory. So no my code does not handle that and it is pointless
> > for it as CPU can not access device memory for me.
> > 
> > That said nothing forbid to add support for ZONE_DEVICE with mbind() like syscall.
> > Thought my personnal preference would still be to avoid use of such generic syscall
> > but have device driver set allocation policy through its own userspace API (device
> > driver could reuse internal of mbind() to achieve the end result).
> > 
> > I am not saying that eveything you want to do is doable now with HMM but, nothing
> > preclude achieving what you want to achieve using ZONE_DEVICE. I really don't think
> > any of the existing mm mechanism (kswapd, lru, numa, ...) are nice fit and can be reuse
> > with device memory.
> > 
> > Each device is so different from the other that i don't believe in a one API fit all.
> > The drm GPU subsystem of the kernel is a testimony of how little can be share when it
> > comes to GPU. The only common code is modesetting. Everything that deals with how to
> > use GPU to compute stuff is per device and most of the logic is in userspace. So i do
> > not see any commonality that could be abstracted at syscall level. I would rather let
> > device driver stack (kernel and userspace) take such decision and have the higher level
> > API (OpenCL, Cuda, C++17, ...) expose something that make sense for each of them.
> > Programmer target those high level API and they intend to use the mechanism each offer
> > to manage memory and memory placement. I would say forcing them to use a second linux
> > specific API to achieve the latter is wrong, at lest for now.
> > 
> > So in the end if the mbind() syscall is done by the userspace side of the device driver
> > then why not just having the device driver communicate this through its own kernel
> > API (which can be much more expressive than what standardize syscall offers). I would
> > rather avoid making change to any syscall for now.
> > 
> > If latter, down the road, once the userspace ecosystem stabilize, we see that there
> > is a good level at which we can abstract memory policy for enough devices then and
> > only then it would make sense to either introduce new syscall or grow/modify existing
> > one. Right now i fear we could only make bad decision that we would regret down the
> > road.
> > 
> > I think we can achieve memory device support with the minimum amount of changes to mm
> > code and existing mm mechanism. Using ZONE_DEVICE already make sure that such memory
> > is kept out of most mm mechanism and hence avoid all the changes you had to make for
> > CDM node. It just looks a better fit from my point of view. I think it is worth
> > considering for your use case too. I am sure folks writting the device driver would
> > rather share more code between platform with grown up bus system (CAPI, CCIX, ...)
> > vs platform with kid bus system (PCIE let's forget about PCI and ISA :))
> 
> Because of coherent access between the CPU and the device, the intention is to use
> the same buffer (VMA) accessed between CPU and device interchangeably through out
> the run time of the application depending upon which side is accessing more and
> how much of performance benefit it will provide after the migration. Now driver
> managed memory is non LRU (whether we use ZONE_DEVICE or not) and we had issues
> migrating non LRU pages mapped in user space. I am not sure whether Minchan had
> changed the basic non LRU migration enablement code to support mapped non LRU
> pages well. So in that case how we are going to migrate back and forth between
> system RAM and device memory ?

In my patchset there is no policy, it is all under device driver control which
decide what range of memory is migrated and when. I think only device driver as
proper knowledge to make such decision. By coalescing data from GPU counters and
request from application made through the uppler level programming API like
Cuda.

Note that even on PCIE the GPU can access the system memory coherently, it is the
reverse that is not doable (and there are limitation on the kind of atomic op the
device can do on system memory). So the hmm_mirror also allow that.

Cheers,
Jérôme

[toc] | [prev] | [next] | [standalone]

#1509304

On 10/26/2016 12:22 AM, Jerome Glisse wrote:
> On Tue, Oct 25, 2016 at 11:01:08PM +0530, Aneesh Kumar K.V wrote:
>> Jerome Glisse <j.glisse@gmail.com> writes:
>>
>>> On Tue, Oct 25, 2016 at 10:29:38AM +0530, Aneesh Kumar K.V wrote:
>>>> Jerome Glisse <j.glisse@gmail.com> writes:
>>>>> On Mon, Oct 24, 2016 at 10:01:49AM +0530, Anshuman Khandual wrote:
>>>
>>> [...]
>>>
>>>>> You can take a look at hmm-v13 if you want to see how i do non LRU page
>>>>> migration. While i put most of the migration code inside hmm_migrate.c it
>>>>> could easily be move to migrate.c without hmm_ prefix.
>>>>>
>>>>> There is 2 missing piece with existing migrate code. First is to put memory
>>>>> allocation for destination under control of who call the migrate code. Second
>>>>> is to allow offloading the copy operation to device (ie not use the CPU to
>>>>> copy data).
>>>>>
>>>>> I believe same requirement also make sense for platform you are targeting.
>>>>> Thus same code can be use.
>>>>>
>>>>> hmm-v13 https://cgit.freedesktop.org/~glisse/linux/log/?h=hmm-v13
>>>>>
>>>>> I haven't posted this patchset yet because we are doing some modifications
>>>>> to the device driver API to accomodate some new features. But the ZONE_DEVICE
>>>>> changes and the overall migration code will stay the same more or less (i have
>>>>> patches that move it to migrate.c and share more code with existing migrate
>>>>> code).
>>>>>
>>>>> If you think i missed anything about lru and page cache please point it to
>>>>> me. Because when i audited code for that i didn't see any road block with
>>>>> the few fs i was looking at (ext4, xfs and core page cache code).
>>>>>
>>>>
>>>> The other restriction around ZONE_DEVICE is, it is not a managed zone.
>>>> That prevents any direct allocation from coherent device by application.
>>>> ie, we would like to force allocation from coherent device using
>>>> interface like mbind(MPOL_BIND..) . Is that possible with ZONE_DEVICE ?
>>>
>>> To achieve this we rely on device fault code path ie when device take a page fault
>>> with help of HMM it will use existing memory if any for fault address but if CPU
>>> page table is empty (and it is not file back vma because of readback) then device
>>> can directly allocate device memory and HMM will update CPU page table to point to
>>> newly allocated device memory.
>>>
>>
>> That is ok if the device touch the page first. What if we want the
>> allocation touched first by cpu to come from GPU ?. Should we always
>> depend on GPU driver to migrate such pages later from system RAM to GPU
>> memory ?
>>
> 
> I am not sure what kind of workload would rather have every first CPU access for
> a range to use device memory. So no my code does not handle that and it is pointless
> for it as CPU can not access device memory for me.

If the user space application can explicitly allocate device memory directly, we
can save one round of migration when the device start accessing it. But then one
can argue what problem statement the device would work on on a freshly allocated
memory which has not been accessed by CPU for loading the data yet. Will look into
this scenario in more detail.

> 
> That said nothing forbid to add support for ZONE_DEVICE with mbind() like syscall.
> Thought my personnal preference would still be to avoid use of such generic syscall
> but have device driver set allocation policy through its own userspace API (device
> driver could reuse internal of mbind() to achieve the end result).

Okay, the basic premise of CDM node is to have a LRU based design where we can
avoid use of driver specific user space memory management code altogether.

> 
> I am not saying that eveything you want to do is doable now with HMM but, nothing
> preclude achieving what you want to achieve using ZONE_DEVICE. I really don't think
> any of the existing mm mechanism (kswapd, lru, numa, ...) are nice fit and can be reuse
> with device memory.

With CDM node based design, the expectation is to get all/maximum core VM mechanism
working so that, driver has to do less device specific optimization.

> 
> Each device is so different from the other that i don't believe in a one API fit all.

Right, so as I had mentioned in the cover letter, pglist_data->coherent_device actually
can become a bit mask indicating the type of coherent device the node is and that can
be used to implement multiple types of requirement in core mm for various kinds of
devices in the future.

> The drm GPU subsystem of the kernel is a testimony of how little can be share when it
> comes to GPU. The only common code is modesetting. Everything that deals with how to
> use GPU to compute stuff is per device and most of the logic is in userspace. So i do

Whats the basic reason which prevents such code/functionality sharing ?

> not see any commonality that could be abstracted at syscall level. I would rather let
> device driver stack (kernel and userspace) take such decision and have the higher level
> API (OpenCL, Cuda, C++17, ...) expose something that make sense for each of them.
> Programmer target those high level API and they intend to use the mechanism each offer
> to manage memory and memory placement. I would say forcing them to use a second linux
> specific API to achieve the latter is wrong, at lest for now.

But going forward dont we want a more closely integrated coherent device solution
which does not depend too much on a device driver stack ? and can be used from a
basic user space program ?

[toc] | [prev] | [next] | [standalone]

#1509581

On Wed, Oct 26, 2016 at 06:26:02PM +0530, Anshuman Khandual wrote:
> On 10/26/2016 12:22 AM, Jerome Glisse wrote:
> > On Tue, Oct 25, 2016 at 11:01:08PM +0530, Aneesh Kumar K.V wrote:
> >> Jerome Glisse <j.glisse@gmail.com> writes:
> >>
> >>> On Tue, Oct 25, 2016 at 10:29:38AM +0530, Aneesh Kumar K.V wrote:
> >>>> Jerome Glisse <j.glisse@gmail.com> writes:
> >>>>> On Mon, Oct 24, 2016 at 10:01:49AM +0530, Anshuman Khandual wrote:
> >>>
> >>> [...]
> >>>
> >>>>> You can take a look at hmm-v13 if you want to see how i do non LRU page
> >>>>> migration. While i put most of the migration code inside hmm_migrate.c it
> >>>>> could easily be move to migrate.c without hmm_ prefix.
> >>>>>
> >>>>> There is 2 missing piece with existing migrate code. First is to put memory
> >>>>> allocation for destination under control of who call the migrate code. Second
> >>>>> is to allow offloading the copy operation to device (ie not use the CPU to
> >>>>> copy data).
> >>>>>
> >>>>> I believe same requirement also make sense for platform you are targeting.
> >>>>> Thus same code can be use.
> >>>>>
> >>>>> hmm-v13 https://cgit.freedesktop.org/~glisse/linux/log/?h=hmm-v13
> >>>>>
> >>>>> I haven't posted this patchset yet because we are doing some modifications
> >>>>> to the device driver API to accomodate some new features. But the ZONE_DEVICE
> >>>>> changes and the overall migration code will stay the same more or less (i have
> >>>>> patches that move it to migrate.c and share more code with existing migrate
> >>>>> code).
> >>>>>
> >>>>> If you think i missed anything about lru and page cache please point it to
> >>>>> me. Because when i audited code for that i didn't see any road block with
> >>>>> the few fs i was looking at (ext4, xfs and core page cache code).
> >>>>>
> >>>>
> >>>> The other restriction around ZONE_DEVICE is, it is not a managed zone.
> >>>> That prevents any direct allocation from coherent device by application.
> >>>> ie, we would like to force allocation from coherent device using
> >>>> interface like mbind(MPOL_BIND..) . Is that possible with ZONE_DEVICE ?
> >>>
> >>> To achieve this we rely on device fault code path ie when device take a page fault
> >>> with help of HMM it will use existing memory if any for fault address but if CPU
> >>> page table is empty (and it is not file back vma because of readback) then device
> >>> can directly allocate device memory and HMM will update CPU page table to point to
> >>> newly allocated device memory.
> >>>
> >>
> >> That is ok if the device touch the page first. What if we want the
> >> allocation touched first by cpu to come from GPU ?. Should we always
> >> depend on GPU driver to migrate such pages later from system RAM to GPU
> >> memory ?
> >>
> > 
> > I am not sure what kind of workload would rather have every first CPU access for
> > a range to use device memory. So no my code does not handle that and it is pointless
> > for it as CPU can not access device memory for me.
> 
> If the user space application can explicitly allocate device memory directly, we
> can save one round of migration when the device start accessing it. But then one
> can argue what problem statement the device would work on on a freshly allocated
> memory which has not been accessed by CPU for loading the data yet. Will look into
> this scenario in more detail.
> 
> > 
> > That said nothing forbid to add support for ZONE_DEVICE with mbind() like syscall.
> > Thought my personnal preference would still be to avoid use of such generic syscall
> > but have device driver set allocation policy through its own userspace API (device
> > driver could reuse internal of mbind() to achieve the end result).
> 
> Okay, the basic premise of CDM node is to have a LRU based design where we can
> avoid use of driver specific user space memory management code altogether.

And i think it is not a good fit, at least not for GPU. GPU device driver have a
big chunk of code dedicated to memory management. You can look at drm/ttm and at
userspace (most is in userspace). It is not because we want to reinvent the wheel
it is because they are some unique constraint.


> > 
> > I am not saying that eveything you want to do is doable now with HMM but, nothing
> > preclude achieving what you want to achieve using ZONE_DEVICE. I really don't think
> > any of the existing mm mechanism (kswapd, lru, numa, ...) are nice fit and can be reuse
> > with device memory.
> 
> With CDM node based design, the expectation is to get all/maximum core VM mechanism
> working so that, driver has to do less device specific optimization.

I think this is a bad idea, today, for GPU but i might be wrong.
 
> > 
> > Each device is so different from the other that i don't believe in a one API fit all.
> 
> Right, so as I had mentioned in the cover letter, pglist_data->coherent_device actually
> can become a bit mask indicating the type of coherent device the node is and that can
> be used to implement multiple types of requirement in core mm for various kinds of
> devices in the future.

I really don't want to move GPU memory management into core mm, if you only concider GPGPU
then it _might_ make sense but for graphic side i definitly don't think so. There are way
to much device specific consideration to have in respect of memory management for GPU
(not only in between different vendor but difference between different generation).

 
> > The drm GPU subsystem of the kernel is a testimony of how little can be share when it
> > comes to GPU. The only common code is modesetting. Everything that deals with how to
> > use GPU to compute stuff is per device and most of the logic is in userspace. So i do
> 
> Whats the basic reason which prevents such code/functionality sharing ?

While the higher level API (OpenGL, OpenCL, Vulkan, Cuda, ...) offer an abstraction model,
they are all different abstractions. They are just no way to have kernel expose a common
API that would allow all of the above to be implemented.

Each GPU have complex memory management and requirement (not only differ between vendor
but also between generation of same vendor). They have different isa for each generation.
They have different way to schedule job for each generation. They offer different sync
mechanism. They have different page table format, mmu, ...

Basicly each GPU generation is a platform on it is own, like arm, ppc, x86, ... so i do
not see a way to expose a common API and i don't think anyone who as work on any number
of GPU see one either. I wish but it is just not the case.

 
> > not see any commonality that could be abstracted at syscall level. I would rather let
> > device driver stack (kernel and userspace) take such decision and have the higher level
> > API (OpenCL, Cuda, C++17, ...) expose something that make sense for each of them.
> > Programmer target those high level API and they intend to use the mechanism each offer
> > to manage memory and memory placement. I would say forcing them to use a second linux
> > specific API to achieve the latter is wrong, at lest for now.
> 
> But going forward dont we want a more closely integrated coherent device solution
> which does not depend too much on a device driver stack ? and can be used from a
> basic user space program ?

That is something i want, but i strongly believe we are not there yet, we have no real
world experience. All we have in the open source community is the graphic stack (drm)
and the graphic stack clearly shows that today there is no common denominator between
GPU outside of modesetting.

So while i share the same aim, i think for now we need to have real experience. Once we
have something like OpenCL >= 2.0, C++17 and couple other userspace API being actively
use on linux with different coherent devices then we can start looking at finding a
common denominator that make sense for enough devices.

I am sure device driver would like to get rid of their custom memory management but i
don't think this is applicable now. I fear existing mm code would always make the worst
decision when it comes to memory placement, migration and reclaim.

Cheers,
Jérôme

[toc] | [prev] | [next] | [standalone]

#1508235

On 25/10/16 04:09, Jerome Glisse wrote:
> On Mon, Oct 24, 2016 at 10:01:49AM +0530, Anshuman Khandual wrote:
> 
>> [...]
> 
>> 	Core kernel memory features like reclamation, evictions etc. might
>> need to be restricted or modified on the coherent device memory node as
>> they can be performance limiting. The RFC does not propose anything on this
>> yet but it can be looked into later on. For now it just disables Auto NUMA
>> for any VMA which has coherent device memory.
>>
>> 	Seamless integration of coherent device memory with system memory
>> will enable various other features, some of which can be listed as follows.
>>
>> 	a. Seamless migrations between system RAM and the coherent memory
>> 	b. Will have asynchronous and high throughput migrations
>> 	c. Be able to allocate huge order pages from these memory regions
>> 	d. Restrict allocations to a large extent to the tasks using the
>> 	   device for workload acceleration
>>
>> 	Before concluding, will look into the reasons why the existing
>> solutions don't work. There are two basic requirements which have to be
>> satisfies before the coherent device memory can be integrated with core
>> kernel seamlessly.
>>
>> 	a. PFN must have struct page
>> 	b. Struct page must able to be inside standard LRU lists
>>
>> 	The above two basic requirements discard the existing method of
>> device memory representation approaches like these which then requires the
>> need of creating a new framework.
> 
> I do not believe the LRU list is a hard requirement, yes when faulting in
> a page inside the page cache it assumes it needs to be added to lru list.
> But i think this can easily be work around.
> 
> In HMM i am using ZONE_DEVICE and because memory is not accessible from CPU
> (not everyone is bless with decent system bus like CAPI, CCIX, Gen-Z, ...)
> so in my case a file back page must always be spawn first from a regular
> page and once read from disk then i can migrate to GPU page.
> 

I've not seen the HMM patchset, but read from disk will go to ZONE_DEVICE?
Then get migrated?

> So if you accept this intermediary step you can easily use ZONE_DEVICE for
> device memory. This way no lru, no complex dance to make the memory out of
> reach from regular memory allocator.
> 
> I think we would have much to gain if we pool our effort on a single common
> solution for device memory. In my case the device memory is not accessible
> by the CPU (because PCIE restrictions), in your case it is. Thus the only
> difference is that in my case it can not be map inside the CPU page table
> while in yours it can.
> 

I think thats a good idea to pool our efforts at the same time making progress

>>
>> (1) Traditional ioremap
>>
>> 	a. Memory is mapped into kernel (linear and virtual) and user space
>> 	b. These PFNs do not have struct pages associated with it
>> 	c. These special PFNs are marked with special flags inside the PTE
>> 	d. Cannot participate in core VM functions much because of this
>> 	e. Cannot do easy user space migrations
>>
>> (2) Zone ZONE_DEVICE
>>
>> 	a. Memory is mapped into kernel and user space
>> 	b. PFNs do have struct pages associated with it
>> 	c. These struct pages are allocated inside it's own memory range
>> 	d. Unfortunately the struct page's union containing LRU has been
>> 	   used for struct dev_pagemap pointer
>> 	e. Hence it cannot be part of any LRU (like Page cache)
>> 	f. Hence file cached mapping cannot reside on these PFNs
>> 	g. Cannot do easy migrations
>>
>> 	I had also explored non LRU representation of this coherent device
>> memory where the integration with system RAM in the core VM is limited only
>> to the following functions. Not being inside LRU is definitely going to
>> reduce the scope of tight integration with system RAM.
>>
>> (1) Migration support between system RAM and coherent memory
>> (2) Migration support between various coherent memory nodes
>> (3) Isolation of the coherent memory
>> (4) Mapping the coherent memory into user space through driver's
>>     struct vm_operations
>> (5) HW poisoning of the coherent memory
>>
>> 	Allocating the entire memory of the coherent device node right
>> after hot plug into ZONE_MOVABLE (where the memory is already inside the
>> buddy system) will still expose a time window where other user space
>> allocations can come into the coherent device memory node and prevent the
>> intended isolation. So traditional hot plug is not the solution. Hence
>> started looking into CMA based non LRU solution but then hit the following
>> roadblocks.
>>
>> (1) CMA does not support hot plugging of new memory node
>> 	a. CMA area needs to be marked during boot before buddy is
>> 	   initialized
>> 	b. cma_alloc()/cma_release() can happen on the marked area
>> 	c. Should be able to mark the CMA areas just after memory hot plug
>> 	d. cma_alloc()/cma_release() can happen later after the hot plug
>> 	e. This is not currently supported right now
>>
>> (2) Mapped non LRU migration of pages
>> 	a. Recent work from Michan Kim makes non LRU page migratable
>> 	b. But it still does not support migration of mapped non LRU pages
>> 	c. With non LRU CMA reserved, again there are some additional
>> 	   challenges
>>
>> 	With hot pluggable CMA and non LRU mapped migration support there
>> may be an alternate approach to represent coherent device memory. Please
>> do review this RFC proposal and let me know your comments or suggestions.
>> Thank you.
> 
> You can take a look at hmm-v13 if you want to see how i do non LRU page
> migration. While i put most of the migration code inside hmm_migrate.c it
> could easily be move to migrate.c without hmm_ prefix.
> 
> There is 2 missing piece with existing migrate code. First is to put memory
> allocation for destination under control of who call the migrate code. Second
> is to allow offloading the copy operation to device (ie not use the CPU to
> copy data).
> 
> I believe same requirement also make sense for platform you are targeting.
> Thus same code can be use.
> 
> hmm-v13 https://cgit.freedesktop.org/~glisse/linux/log/?h=hmm-v13
> 

Thanks for the link

> I haven't posted this patchset yet because we are doing some modifications
> to the device driver API to accomodate some new features. But the ZONE_DEVICE
> changes and the overall migration code will stay the same more or less (i have
> patches that move it to migrate.c and share more code with existing migrate
> code).
> 
> If you think i missed anything about lru and page cache please point it to
> me. Because when i audited code for that i didn't see any road block with
> the few fs i was looking at (ext4, xfs and core page cache code).
> 
>> [...]
> 
> Cheers,
> Jérôme
> 

Cheers,
Balbir Singh.

[toc] | [prev] | [next] | [standalone]

#1508380

On Tue, Oct 25, 2016 at 11:07:39PM +1100, Balbir Singh wrote:
> On 25/10/16 04:09, Jerome Glisse wrote:
> > On Mon, Oct 24, 2016 at 10:01:49AM +0530, Anshuman Khandual wrote:
> > 
> >> [...]
> > 
> >> 	Core kernel memory features like reclamation, evictions etc. might
> >> need to be restricted or modified on the coherent device memory node as
> >> they can be performance limiting. The RFC does not propose anything on this
> >> yet but it can be looked into later on. For now it just disables Auto NUMA
> >> for any VMA which has coherent device memory.
> >>
> >> 	Seamless integration of coherent device memory with system memory
> >> will enable various other features, some of which can be listed as follows.
> >>
> >> 	a. Seamless migrations between system RAM and the coherent memory
> >> 	b. Will have asynchronous and high throughput migrations
> >> 	c. Be able to allocate huge order pages from these memory regions
> >> 	d. Restrict allocations to a large extent to the tasks using the
> >> 	   device for workload acceleration
> >>
> >> 	Before concluding, will look into the reasons why the existing
> >> solutions don't work. There are two basic requirements which have to be
> >> satisfies before the coherent device memory can be integrated with core
> >> kernel seamlessly.
> >>
> >> 	a. PFN must have struct page
> >> 	b. Struct page must able to be inside standard LRU lists
> >>
> >> 	The above two basic requirements discard the existing method of
> >> device memory representation approaches like these which then requires the
> >> need of creating a new framework.
> > 
> > I do not believe the LRU list is a hard requirement, yes when faulting in
> > a page inside the page cache it assumes it needs to be added to lru list.
> > But i think this can easily be work around.
> > 
> > In HMM i am using ZONE_DEVICE and because memory is not accessible from CPU
> > (not everyone is bless with decent system bus like CAPI, CCIX, Gen-Z, ...)
> > so in my case a file back page must always be spawn first from a regular
> > page and once read from disk then i can migrate to GPU page.
> > 
> 
> I've not seen the HMM patchset, but read from disk will go to ZONE_DEVICE?
> Then get migrated?

Because in my case device memory is not accessible by anything except the device
(not entirely true but for sake of design it is) any page read from disk will be
first read into regular page (from regular system memory). It is only once it is
uptodate and in page cache that it can be migrated to a ZONE_DEVICE page.

So read from disk use an intermediary page. Write back is kind of the same i plan
on using a bounce page by leveraging existing bio bounce infrastructure.

Cheers,
Jérôme

[toc] | [prev] | [next] | [standalone]

#1507526

On 10/23/2016 09:31 PM, Anshuman Khandual wrote:
> 	To achieve seamless integration  between system RAM and coherent
> device memory it must be able to utilize core memory kernel features like
> anon mapping, file mapping, page cache, driver managed pages, HW poisoning,
> migrations, reclaim, compaction, etc.

So, you need to support all these things, but not autonuma or hugetlbfs?
 What's the reasoning behind that?

If you *really* don't want a "cdm" page to be migrated, then why isn't
that policy set on the VMA in the first place?  That would keep "cdm"
pages from being made non-cdm.  And, why would autonuma ever make a
non-cdm page and migrate it in to cdm?  There will be no NUMA access
faults caused by the devices that are fed to autonuma.

I'm confused.

[toc] | [prev] | [next] | [standalone]

#1507570

On 10/24/2016 01:04 PM, Dave Hansen wrote:

> On 10/23/2016 09:31 PM, Anshuman Khandual wrote:
>> 	To achieve seamless integration  between system RAM and coherent
>> device memory it must be able to utilize core memory kernel features like
>> anon mapping, file mapping, page cache, driver managed pages, HW poisoning,
>> migrations, reclaim, compaction, etc.
> So, you need to support all these things, but not autonuma or hugetlbfs?
>   What's the reasoning behind that?
>
> If you *really* don't want a "cdm" page to be migrated, then why isn't
> that policy set on the VMA in the first place?  That would keep "cdm"
> pages from being made non-cdm.  And, why would autonuma ever make a
> non-cdm page and migrate it in to cdm?  There will be no NUMA access
> faults caused by the devices that are fed to autonuma.
>
Pages are desired to be migrateable, both into (starting cpu zone 
movable->cdm) and out of (starting cdm->cpu zone movable) but only 
through explicit migration, not via autonuma.  other pages in the same 
VMA should still be migrateable between CPU nodes via autonuma however.

Its expected a lot of these allocations are going to end up in THPs.  
I'm not sure we need to explicitly disallow hugetlbfs support but the 
identified use case is definitely via THPs not tlbfs.

[toc] | [prev] | [next] | [standalone]

#1507663

On 10/24/2016 11:32 AM, David Nellans wrote:
> On 10/24/2016 01:04 PM, Dave Hansen wrote:
>> If you *really* don't want a "cdm" page to be migrated, then why isn't
>> that policy set on the VMA in the first place?  That would keep "cdm"
>> pages from being made non-cdm.  And, why would autonuma ever make a
>> non-cdm page and migrate it in to cdm?  There will be no NUMA access
>> faults caused by the devices that are fed to autonuma.
>>
> Pages are desired to be migrateable, both into (starting cpu zone
> movable->cdm) and out of (starting cdm->cpu zone movable) but only
> through explicit migration, not via autonuma.

OK, and is there a reason that the existing mbind code plus NUMA
policies fails to give you this behavior?

Does autonuma somehow override strict NUMA binding?

>  other pages in the same
> VMA should still be migrateable between CPU nodes via autonuma however.

That's not the way the implementation here works, as I understand it.
See the VM_CDM patch and my responses to it.

> Its expected a lot of these allocations are going to end up in THPs. 
> I'm not sure we need to explicitly disallow hugetlbfs support but the
> identified use case is definitely via THPs not tlbfs.

I think THP and hugetlbfs are implementations, not use cases. :)

Is it too hard to support hugetlbfs that we should complicate its code
to exclude it from this type of memory?  Why?

[toc] | [prev] | [standalone]

Page 2 of 2 — ← Prev page 1 [2]

Back to top | Article view | linux.kernel

csiph-web