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

Groups > linux.kernel > #1643173 > unrolled thread

Re: [RFC 1/6] mm, page_alloc: fix more premature OOM due to race with cpuset update

Back to article view | Back to linux.kernel

This discussion starts older than the indexed window; earlier articles aren't shown. The article labeled Started by below is the oldest one visible, not the original post.

Contents

  Re: [RFC 1/6] mm, page_alloc: fix more premature OOM due to race  with cpuset update Michal Hocko <mhocko@kernel.org> - 2017-05-17 11:30 +0200
    Re: [RFC 1/6] mm, page_alloc: fix more premature OOM due to race  with cpuset update Christoph Lameter <cl@linux.com> - 2017-05-17 16:00 +0200
      Re: [RFC 1/6] mm, page_alloc: fix more premature OOM due to race  with cpuset update Michal Hocko <mhocko@kernel.org> - 2017-05-17 16:10 +0200
        Re: [RFC 1/6] mm, page_alloc: fix more premature OOM due to race  with cpuset update Christoph Lameter <cl@linux.com> - 2017-05-17 16:50 +0200
          Re: [RFC 1/6] mm, page_alloc: fix more premature OOM due to race  with cpuset update Michal Hocko <mhocko@kernel.org> - 2017-05-17 17:00 +0200
            Re: [RFC 1/6] mm, page_alloc: fix more premature OOM due to race  with cpuset update Christoph Lameter <cl@linux.com> - 2017-05-17 17:30 +0200
            Re: [RFC 1/6] mm, page_alloc: fix more premature OOM due to race  with cpuset update Christoph Lameter <cl@linux.com> - 2017-05-17 17:30 +0200
              Re: [RFC 1/6] mm, page_alloc: fix more premature OOM due to race  with cpuset update Michal Hocko <mhocko@kernel.org> - 2017-05-18 11:10 +0200
                Re: [RFC 1/6] mm, page_alloc: fix more premature OOM due to race  with cpuset update Christoph Lameter <cl@linux.com> - 2017-05-18 19:00 +0200
                  Re: [RFC 1/6] mm, page_alloc: fix more premature OOM due to race  with cpuset update Michal Hocko <mhocko@kernel.org> - 2017-05-18 19:30 +0200
                    Re: [RFC 1/6] mm, page_alloc: fix more premature OOM due to race  with cpuset update Christoph Lameter <cl@linux.com> - 2017-05-18 21:10 +0200
                      Re: [RFC 1/6] mm, page_alloc: fix more premature OOM due to race  with cpuset update Michal Hocko <mhocko@kernel.org> - 2017-05-19 09:40 +0200
          Re: [RFC 1/6] mm, page_alloc: fix more premature OOM due to race with  cpuset update Vlastimil Babka <vbabka@suse.cz> - 2017-05-18 12:10 +0200
            Re: [RFC 1/6] mm, page_alloc: fix more premature OOM due to race  with cpuset update Christoph Lameter <cl@linux.com> - 2017-05-18 19:10 +0200
              Re: [RFC 1/6] mm, page_alloc: fix more premature OOM due to race with  cpuset update Vlastimil Babka <vbabka@suse.cz> - 2017-05-19 13:30 +0200

#1643173 — Re: [RFC 1/6] mm, page_alloc: fix more premature OOM due to race with cpuset update

On Sun 30-04-17 16:33:10, Cristopher Lameter wrote:
> On Wed, 26 Apr 2017, Vlastimil Babka wrote:
> 
> > > Such an application typically already has such logic and executes a
> > > binding after discovering its numa node configuration on startup. It would
> > > have to be modified to redo that action when it gets some sort of a signal
> > > from the script telling it that the node config would be changed.
> > >
> > > Having this logic in the application instead of the kernel avoids all the
> > > kernel messes that we keep on trying to deal with and IMHO is much
> > > cleaner.
> >
> > That would be much simpler for us indeed. But we still IMHO can't
> > abruptly start denying page fault allocations for existing applications
> > that don't have the necessary awareness.
> 
> We certainly can do that. The failure of the page faults are due to the
> admin trying to move an application that is not aware of this and is using
> mempols. That could be an error. Trying to move an application that
> contains both absolute and relative node numbers is definitely something
> that is potentiall so screwed up that the kernel should not muck around
> with such an app.
> 
> Also user space can determine if the application is using memory policies
> and can then take appropriate measures (message to the sysadmin to eval
> tge situation f.e.) or mess aroud with the processes memory policies on
> its own.
> 
> So this is certainly a way out of this mess.

So how are you going to distinguish VM_FAULT_OOM from an empty mempolicy
case in a raceless way?

-- 
Michal Hocko
SUSE Labs

[toc] | [next] | [standalone]

#1643373

On Wed, 17 May 2017, Michal Hocko wrote:

> > We certainly can do that. The failure of the page faults are due to the
> > admin trying to move an application that is not aware of this and is using
> > mempols. That could be an error. Trying to move an application that
> > contains both absolute and relative node numbers is definitely something
> > that is potentiall so screwed up that the kernel should not muck around
> > with such an app.
> >
> > Also user space can determine if the application is using memory policies
> > and can then take appropriate measures (message to the sysadmin to eval
> > tge situation f.e.) or mess aroud with the processes memory policies on
> > its own.
> >
> > So this is certainly a way out of this mess.
>
> So how are you going to distinguish VM_FAULT_OOM from an empty mempolicy
> case in a raceless way?

You dont have to do that if you do not create an empty mempolicy in the
first place. The current kernel code avoids that by first allowing access
to the new set of nodes and removing the old ones from the set when done.

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

#1643379

On Wed 17-05-17 08:56:34, Cristopher Lameter wrote:
> On Wed, 17 May 2017, Michal Hocko wrote:
> 
> > > We certainly can do that. The failure of the page faults are due to the
> > > admin trying to move an application that is not aware of this and is using
> > > mempols. That could be an error. Trying to move an application that
> > > contains both absolute and relative node numbers is definitely something
> > > that is potentiall so screwed up that the kernel should not muck around
> > > with such an app.
> > >
> > > Also user space can determine if the application is using memory policies
> > > and can then take appropriate measures (message to the sysadmin to eval
> > > tge situation f.e.) or mess aroud with the processes memory policies on
> > > its own.
> > >
> > > So this is certainly a way out of this mess.
> >
> > So how are you going to distinguish VM_FAULT_OOM from an empty mempolicy
> > case in a raceless way?
> 
> You dont have to do that if you do not create an empty mempolicy in the
> first place. The current kernel code avoids that by first allowing access
> to the new set of nodes and removing the old ones from the set when done.

which is racy and as Vlastimil pointed out. If we simply fail such an
allocation the failure will go up the call chain until we hit the OOM
killer due to VM_FAULT_OOM. How would you want to handle that?
-- 
Michal Hocko
SUSE Labs

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

#1643410

On Wed, 17 May 2017, Michal Hocko wrote:

> > > So how are you going to distinguish VM_FAULT_OOM from an empty mempolicy
> > > case in a raceless way?
> >
> > You dont have to do that if you do not create an empty mempolicy in the
> > first place. The current kernel code avoids that by first allowing access
> > to the new set of nodes and removing the old ones from the set when done.
>
> which is racy and as Vlastimil pointed out. If we simply fail such an
> allocation the failure will go up the call chain until we hit the OOM
> killer due to VM_FAULT_OOM. How would you want to handle that?

The race is where? If you expand the node set during the move of the
application then you are safe in terms of the legacy apps that did not
include static bindings.

If you have screwy things like static mbinds in there then you are
hopelessly lost anyways. You may have moved the process to another set
of nodes but the static bindings may refer to a node no longer
available. Thus the OOM is legitimate.

At least a user space app could inspect
the situation and come up with custom ways of dealing with the mess.

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

#1643440

On Wed 17-05-17 09:48:25, Cristopher Lameter wrote:
> On Wed, 17 May 2017, Michal Hocko wrote:
> 
> > > > So how are you going to distinguish VM_FAULT_OOM from an empty mempolicy
> > > > case in a raceless way?
> > >
> > > You dont have to do that if you do not create an empty mempolicy in the
> > > first place. The current kernel code avoids that by first allowing access
> > > to the new set of nodes and removing the old ones from the set when done.
> >
> > which is racy and as Vlastimil pointed out. If we simply fail such an
> > allocation the failure will go up the call chain until we hit the OOM
> > killer due to VM_FAULT_OOM. How would you want to handle that?
> 
> The race is where? If you expand the node set during the move of the
> application then you are safe in terms of the legacy apps that did not
> include static bindings.

I am pretty sure it is describe in those changelogs and I won't repeat
it here.

> If you have screwy things like static mbinds in there then you are
> hopelessly lost anyways. You may have moved the process to another set
> of nodes but the static bindings may refer to a node no longer
> available. Thus the OOM is legitimate.

The point is that you do _not_ want such a process to trigger the OOM
because it can cause other processes being killed.

> At least a user space app could inspect
> the situation and come up with custom ways of dealing with the mess.

I do not really see how would this help to prevent a malicious user from
playing tricks.

-- 
Michal Hocko
SUSE Labs

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

#1643460

On Wed, 17 May 2017, Michal Hocko wrote:

> > The race is where? If you expand the node set during the move of the
> > application then you are safe in terms of the legacy apps that did not
> > include static bindings.
>
> I am pretty sure it is describe in those changelogs and I won't repeat
> it here.

I cannot figure out what you are referring to. There are numerous
patches and discussions about OOM scenarios in this context.

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

#1643464

On Wed, 17 May 2017, Michal Hocko wrote:

> > If you have screwy things like static mbinds in there then you are
> > hopelessly lost anyways. You may have moved the process to another set
> > of nodes but the static bindings may refer to a node no longer
> > available. Thus the OOM is legitimate.
>
> The point is that you do _not_ want such a process to trigger the OOM
> because it can cause other processes being killed.

Nope. The OOM in a cpuset gets the process doing the alloc killed. Or what
that changed?

At this point you have messed up royally and nothing is going to rescue
you anyways. OOM or not does not matter anymore. The app will fail.

> > At least a user space app could inspect
> > the situation and come up with custom ways of dealing with the mess.
>
> I do not really see how would this help to prevent a malicious user from
> playing tricks.

How did a malicious user come into this? Of course you can mess up in
significant ways if you can overflow nodes and cause an app that has
restrictions to fail but nothing is going to change that.

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

#1643998

On Wed 17-05-17 10:25:09, Cristopher Lameter wrote:
> On Wed, 17 May 2017, Michal Hocko wrote:
> 
> > > If you have screwy things like static mbinds in there then you are
> > > hopelessly lost anyways. You may have moved the process to another set
> > > of nodes but the static bindings may refer to a node no longer
> > > available. Thus the OOM is legitimate.
> >
> > The point is that you do _not_ want such a process to trigger the OOM
> > because it can cause other processes being killed.
> 
> Nope. The OOM in a cpuset gets the process doing the alloc killed. Or what
> that changed?
> 
> At this point you have messed up royally and nothing is going to rescue
> you anyways. OOM or not does not matter anymore. The app will fail.

Not really. If you can trick the system to _think_ that the intersection
between mempolicy and the cpuset is empty then the OOM killer might
trigger an innocent task rather than the one which tricked it into that
situation.
-- 
Michal Hocko
SUSE Labs

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

#1644754

On Thu, 18 May 2017, Michal Hocko wrote:

> > Nope. The OOM in a cpuset gets the process doing the alloc killed. Or what
> > that changed?

!!!!!

> >
> > At this point you have messed up royally and nothing is going to rescue
> > you anyways. OOM or not does not matter anymore. The app will fail.
>
> Not really. If you can trick the system to _think_ that the intersection
> between mempolicy and the cpuset is empty then the OOM killer might
> trigger an innocent task rather than the one which tricked it into that
> situation.

See above. OOM Kill in a cpuset does not kill an innocent task but a task
that does an allocation in that specific context meaning a task in that
cpuset that also has a memory policty.

Regardless of that the point earlier was that the moving logic can avoid
creating temporary situations of empty sets of nodes by analysing the
memory policies etc and only performing moves when doing so is safe.

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

#1644776

On Thu 18-05-17 11:57:55, Cristopher Lameter wrote:
> On Thu, 18 May 2017, Michal Hocko wrote:
> 
> > > Nope. The OOM in a cpuset gets the process doing the alloc killed. Or what
> > > that changed?
> 
> !!!!!
> 
> > >
> > > At this point you have messed up royally and nothing is going to rescue
> > > you anyways. OOM or not does not matter anymore. The app will fail.
> >
> > Not really. If you can trick the system to _think_ that the intersection
> > between mempolicy and the cpuset is empty then the OOM killer might
> > trigger an innocent task rather than the one which tricked it into that
> > situation.
> 
> See above. OOM Kill in a cpuset does not kill an innocent task but a task
> that does an allocation in that specific context meaning a task in that
> cpuset that also has a memory policty.

No, the oom killer will chose the largest task in the specific NUMA
domain. If you just fail such an allocation then a page fault would get
VM_FAULT_OOM and pagefault_out_of_memory would kill a task regardless of
the cpusets.
 
> Regardless of that the point earlier was that the moving logic can avoid
> creating temporary situations of empty sets of nodes by analysing the
> memory policies etc and only performing moves when doing so is safe.

How are you going to do that in a raceless way? Moreover the whole
discussion is about _failing_ allocations on an empty cpuset and
mempolicy intersection.

-- 
Michal Hocko
SUSE Labs

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

#1644844

On Thu, 18 May 2017, Michal Hocko wrote:

> > See above. OOM Kill in a cpuset does not kill an innocent task but a task
> > that does an allocation in that specific context meaning a task in that
> > cpuset that also has a memory policty.
>
> No, the oom killer will chose the largest task in the specific NUMA
> domain. If you just fail such an allocation then a page fault would get
> VM_FAULT_OOM and pagefault_out_of_memory would kill a task regardless of
> the cpusets.

Ok someone screwed up that code. There still is the determination that we
have a constrained alloc:

oom_kill:
	/*
         * Check if there were limitations on the allocation (only relevant for
         * NUMA and memcg) that may require different handling.
         */
        constraint = constrained_alloc(oc);
        if (constraint != CONSTRAINT_MEMORY_POLICY)
                oc->nodemask = NULL;
        check_panic_on_oom(oc, constraint);

-- Ok. A constrained failing alloc used to terminate the allocating
	process here. But it falls through to selecting a "bad process"


        if (!is_memcg_oom(oc) && sysctl_oom_kill_allocating_task &&
            current->mm && !oom_unkillable_task(current, NULL, oc->nodemask) &&
            current->signal->oom_score_adj != OOM_SCORE_ADJ_MIN) {
                get_task_struct(current);
                oc->chosen = current;
                oom_kill_process(oc, "Out of memory (oom_kill_allocating_task)");
                return true;
        }

--  A constrained allocation should not get here but fail the process that
	attempts the alloc.

        select_bad_process(oc);


Can we restore the old behavior? If I just specify the right memory policy
I can cause other processes to just be terminated?


> > Regardless of that the point earlier was that the moving logic can avoid
> > creating temporary situations of empty sets of nodes by analysing the
> > memory policies etc and only performing moves when doing so is safe.
>
> How are you going to do that in a raceless way? Moreover the whole
> discussion is about _failing_ allocations on an empty cpuset and
> mempolicy intersection.

Again this is only working for processes that are well behaved and it
never worked in a different way before. There was always the assumption
that a process does not allocate in the areas that have allocation
constraints and that the process does not change memory policies nor
store them somewhere for late etc etc. HPC apps typically allocate memory
on startup and then go through long times of processing and I/O.

The idea that cpuset node to node migration will work with a running
process that does abitrary activity is a pipe dream that we should give
up. There must be constraints on a process in order to allow this to work
and as far as I can tell this is best done in userspace with a library and
by putting requirements on the applications that desire to be movable that
way.

F.e. an application that does not use memory policies or other allocation
constraints should be fine. That has been working.

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

#1645283

On Thu 18-05-17 14:07:45, Cristopher Lameter wrote:
> On Thu, 18 May 2017, Michal Hocko wrote:
> 
> > > See above. OOM Kill in a cpuset does not kill an innocent task but a task
> > > that does an allocation in that specific context meaning a task in that
> > > cpuset that also has a memory policty.
> >
> > No, the oom killer will chose the largest task in the specific NUMA
> > domain. If you just fail such an allocation then a page fault would get
> > VM_FAULT_OOM and pagefault_out_of_memory would kill a task regardless of
> > the cpusets.
> 
> Ok someone screwed up that code. There still is the determination that we
> have a constrained alloc:

It would be much more easier if you read emails more carefully. In order
to have a constrained OOM you have to have either a non-null nodemask or
zonelist which. And as I've said above you do not have them from the
pagefault_out_of_memory context. The whole point of this discussion is
_that_ failing allocations will not work currently!

> oom_kill:
> 	/*
>          * Check if there were limitations on the allocation (only relevant for
>          * NUMA and memcg) that may require different handling.
>          */
>         constraint = constrained_alloc(oc);
>         if (constraint != CONSTRAINT_MEMORY_POLICY)
>                 oc->nodemask = NULL;
>         check_panic_on_oom(oc, constraint);
> 
> -- Ok. A constrained failing alloc used to terminate the allocating
> 	process here. But it falls through to selecting a "bad process"

This behavior is there for ~10 years.
[...]
> Can we restore the old behavior? If I just specify the right memory policy
> I can cause other processes to just be terminated?

Not normally. Because out_of_memory called from the page allocator
context makes sure to kill tasks from the same NUMA domain (see
oom_unkillable_task).
 
> > > Regardless of that the point earlier was that the moving logic can avoid
> > > creating temporary situations of empty sets of nodes by analysing the
> > > memory policies etc and only performing moves when doing so is safe.
> >
> > How are you going to do that in a raceless way? Moreover the whole
> > discussion is about _failing_ allocations on an empty cpuset and
> > mempolicy intersection.
> 
> Again this is only working for processes that are well behaved and it
> never worked in a different way before. There was always the assumption
> that a process does not allocate in the areas that have allocation
> constraints and that the process does not change memory policies nor
> store them somewhere for late etc etc. HPC apps typically allocate memory
> on startup and then go through long times of processing and I/O.

I would call it a bad design which then triggered a lot of work to make
it semi-working over years. This is what Vlastimil tries to address now.
And yes that might mean we would have to do some restrictions on the
semantics. But as you know this is a user visible API and changing
something that has been fundamentally underdefined initially is quite
hard to fix.
-- 
Michal Hocko
SUSE Labs

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

#1644034 — Re: [RFC 1/6] mm, page_alloc: fix more premature OOM due to race with cpuset update

On 05/17/2017 04:48 PM, Christoph Lameter wrote:
> On Wed, 17 May 2017, Michal Hocko wrote:
> 
>>>> So how are you going to distinguish VM_FAULT_OOM from an empty mempolicy
>>>> case in a raceless way?
>>>
>>> You dont have to do that if you do not create an empty mempolicy in the
>>> first place. The current kernel code avoids that by first allowing access
>>> to the new set of nodes and removing the old ones from the set when done.
>>
>> which is racy and as Vlastimil pointed out. If we simply fail such an
>> allocation the failure will go up the call chain until we hit the OOM
>> killer due to VM_FAULT_OOM. How would you want to handle that?
> 
> The race is where? If you expand the node set during the move of the
> application then you are safe in terms of the legacy apps that did not
> include static bindings.

No, that expand/shrink by itself doesn't work against parallel
get_page_from_freelist going through a zonelist. Moving from node 0 to
1, with zonelist containing nodes 1 and 0 in that order:

- mempolicy mask is 0
- zonelist iteration checks node 1, it's not allowed, skip
- mempolicy mask is 0,1 (expand)
- mempolicy mask is 1 (shrink)
- zonelist iteration checks node 0, it's not allowed, skip
- OOM

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

#1644763

On Thu, 18 May 2017, Vlastimil Babka wrote:

> > The race is where? If you expand the node set during the move of the
> > application then you are safe in terms of the legacy apps that did not
> > include static bindings.
>
> No, that expand/shrink by itself doesn't work against parallel

Parallel? I think we are clear that ithis is inherently racy against the
app changing policies etc etc? There is a huge issue there already. The
app needs to be well behaved in some heretofore undefined way in order to
make moves clean.

> get_page_from_freelist going through a zonelist. Moving from node 0 to
> 1, with zonelist containing nodes 1 and 0 in that order:
>
> - mempolicy mask is 0
> - zonelist iteration checks node 1, it's not allowed, skip

There is an allocation from node 1? This is not allowed before the move.
So it should fail. Not skipping to another node.

> - mempolicy mask is 0,1 (expand)
> - mempolicy mask is 1 (shrink)
> - zonelist iteration checks node 0, it's not allowed, skip
> - OOM

Are you talking about a race here between zonelist scanning and the
moving? That has been there forever.

And frankly there are gazillions of these races. The best thing to do is
to get the cpuset moving logic out of the kernel and into user space.

Understand that this is a heuristic and maybe come up with a list of
restrictions that make an app safe. An safe app that can be moved must f.e

1. Not allocate new memory while its being moved
2. Not change memory policies after its initialization and while its being
moved.
3. Not save memory policy state in some variable (because the logic to
translate the memory policies for the new context cannot find it).

...

Again cpuset process migration  is a huge mess that you do not want to
have in the kernel and AFAICT this is a corner case with difficult
semantics. Better have that in user space...

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

#1645530 — Re: [RFC 1/6] mm, page_alloc: fix more premature OOM due to race with cpuset update

On 05/18/2017 07:07 PM, Christoph Lameter wrote:
> On Thu, 18 May 2017, Vlastimil Babka wrote:
> 
>>> The race is where? If you expand the node set during the move of the
>>> application then you are safe in terms of the legacy apps that did not
>>> include static bindings.
>>
>> No, that expand/shrink by itself doesn't work against parallel
> 
> Parallel? I think we are clear that ithis is inherently racy against the
> app changing policies etc etc? There is a huge issue there already. The
> app needs to be well behaved in some heretofore undefined way in order to
> make moves clean.

The code is safe against mbind() changing a vma's mempolicy parallel to
another thread page faulting within that vma, because mbind() takes
mmap_sem for write, and page faults take it for read. The per-task
mempolicy can be changed by set_mempolicy() call which means the task
itself doesn't allocate stuff in parallel.
So, the application never needed to be "well behaved" wrt changing its
own mempolicies.

Now with mempolicy rebinding due to cpuset migrations, the application
cannot be "well behaved" as it has no way to learn about being under a
cpuset, or cpuset change. Any application can be put in a cpuset and we
can't really expect that all would be adapted, even if the necessary
interfaces existed. Thus, the rebinding implementation in the kernel
itself has to be robust against parallel allocations.

>> get_page_from_freelist going through a zonelist. Moving from node 0 to
>> 1, with zonelist containing nodes 1 and 0 in that order:
>>
>> - mempolicy mask is 0
>> - zonelist iteration checks node 1, it's not allowed, skip
> 
> There is an allocation from node 1?

Sorry, I missed to mention the full scenario. Let's say the allocation
is on cpu local to node 1, so it gets zonelist from node 1, which
contains nodes 1 and 0 in that order.

> This is not allowed before the move.
> So it should fail. Not skipping to another node.
> 
>> - mempolicy mask is 0,1 (expand)
>> - mempolicy mask is 1 (shrink)
>> - zonelist iteration checks node 0, it's not allowed, skip
>> - OOM
> 
> Are you talking about a race here between zonelist scanning and the
> moving? That has been there forever.

As far as I can tell from my git archeology in [1] there was always some
kind of protection against the race (generation counters, two-step
protocol, seqlock...), which however had some corner cases. This patch
is merely plugging the last known one.

> And frankly there are gazillions of these races.

I don't know about any other existing race that we don't handle after
this patch.

> The best thing to do is
> to get the cpuset moving logic out of the kernel and into user space.
> 
> Understand that this is a heuristic and maybe come up with a list of
> restrictions that make an app safe. An safe app that can be moved must f.e
> 
> 1. Not allocate new memory while its being moved
> 2. Not change memory policies after its initialization and while its being
> moved.

As I explainer eariler in this mail, changing mempolicy by app itself is
safe, the problem was always due to cpuset-triggered rebinding.

> 3. Not save memory policy state in some variable (because the logic to
> translate the memory policies for the new context cannot find it).
> 
> ...
> 
> Again cpuset process migration  is a huge mess that you do not want to
> have in the kernel and AFAICT this is a corner case with difficult
> semantics. Better have that in user space...

Moving this out of kernel etc is changing the current semantics and
breaking existing userspace, this patch is a fix within the existing one.

[1] https://marc.info/?l=linux-mm&m=148611344511408&w=2


> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@kvack.org.  For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
> 

[toc] | [prev] | [standalone]

Back to top | Article view | linux.kernel

csiph-web