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Groups > linux.kernel > #1646543 > unrolled thread
| Started by | "Mike Rapoport" <rppt@linux.vnet.ibm.com> |
|---|---|
| First post | 2017-05-22 08:20 +0200 |
| Last post | 2017-05-24 17:20 +0200 |
| Articles | 9 on this page of 49 — 8 participants |
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[PATCH] mm: introduce MADV_CLR_HUGEPAGE "Mike Rapoport" <rppt@linux.vnet.ibm.com> - 2017-05-22 08:20 +0200
Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Anshuman Khandual <khandual@linux.vnet.ibm.com> - 2017-05-22 09:30 +0200
Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Mike Rapoport <rppt@linux.vnet.ibm.com> - 2017-05-22 10:20 +0200
Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE "Kirill A. Shutemov" <kirill@shutemov.name> - 2017-05-22 13:50 +0200
Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Mike Rapoport <rppt@linux.vnet.ibm.com> - 2017-05-22 15:40 +0200
Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE "Kirill A. Shutemov" <kirill@shutemov.name> - 2017-05-22 15:50 +0200
Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Michal Hocko <mhocko@kernel.org> - 2017-05-22 16:00 +0200
Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Mike Rapoport <rppt@linux.vnet.ibm.com> - 2017-05-22 16:30 +0200
Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Vlastimil Babka <vbabka@suse.cz> - 2017-05-22 18:00 +0200
Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Mike Rapoport <rppt@linux.vnet.ibm.com> - 2017-05-22 20:00 +0200
Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Mike Rapoport <rppt@linux.vnet.ibm.com> - 2017-05-24 10:00 +0200
Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Vlastimil Babka <vbabka@suse.cz> - 2017-05-24 10:10 +0200
Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Mike Rapoport <rppt@linux.vnet.ibm.com> - 2017-05-24 12:50 +0200
Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Michal Hocko <mhocko@kernel.org> - 2017-05-24 13:20 +0200
Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Mike Rapoport <rppt@linux.vnet.ibm.com> - 2017-05-24 16:30 +0200
Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Andrea Arcangeli <aarcange@redhat.com> - 2017-05-24 17:30 +0200
Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Michal Hocko <mhocko@kernel.org> - 2017-05-30 09:50 +0200
Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Mike Rapoport <rppt@linux.vnet.ibm.com> - 2017-05-30 12:20 +0200
Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Michal Hocko <mhocko@kernel.org> - 2017-05-30 12:50 +0200
Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Andrea Arcangeli <aarcange@redhat.com> - 2017-05-30 16:10 +0200
Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Michal Hocko <mhocko@kernel.org> - 2017-05-30 16:50 +0200
Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Michal Hocko <mhocko@kernel.org> - 2017-05-30 17:00 +0200
Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Andrea Arcangeli <aarcange@redhat.com> - 2017-05-30 18:10 +0200
Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Vlastimil Babka <vbabka@suse.cz> - 2017-05-31 08:40 +0200
Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Michal Hocko <mhocko@kernel.org> - 2017-05-31 10:30 +0200
Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Mike Rapoport <rppt@linux.vnet.ibm.com> - 2017-05-31 11:30 +0200
Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Michal Hocko <mhocko@kernel.org> - 2017-05-31 12:30 +0200
Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Michal Hocko <mhocko@kernel.org> - 2017-05-31 12:30 +0200
Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Mike Rapoport <rppt@linux.vnet.ibm.com> - 2017-06-01 13:10 +0200
Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Michal Hocko <mhocko@kernel.org> - 2017-06-01 14:30 +0200
Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Andrea Arcangeli <aarcange@redhat.com> - 2017-05-30 17:50 +0200
Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Michal Hocko <mhocko@kernel.org> - 2017-05-31 14:10 +0200
Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Mike Rapoprt <rppt@linux.vnet.ibm.com> - 2017-05-31 14:40 +0200
Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Andrea Arcangeli <aarcange@redhat.com> - 2017-05-31 16:20 +0200
Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Michal Hocko <mhocko@kernel.org> - 2017-05-31 16:40 +0200
Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Andrea Arcangeli <aarcange@redhat.com> - 2017-05-31 17:50 +0200
Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Mike Rapoport <rppt@linux.vnet.ibm.com> - 2017-06-01 09:00 +0200
Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Michal Hocko <mhocko@kernel.org> - 2017-05-31 16:20 +0200
Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Mike Rapoport <rppt@linux.vnet.ibm.com> - 2017-06-01 09:00 +0200
Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Michal Hocko <mhocko@kernel.org> - 2017-06-01 10:10 +0200
Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Mike Rapoport <rppt@linux.vnet.ibm.com> - 2017-06-01 10:40 +0200
Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Andrea Arcangeli <aarcange@redhat.com> - 2017-06-01 15:50 +0200
Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Mike Rapoport <rppt@linux.vnet.ibm.com> - 2017-06-02 11:20 +0200
Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Mike Rapoport <rppt@linux.vnet.ibm.com> - 2017-05-31 11:10 +0200
Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Michal Hocko <mhocko@kernel.org> - 2017-05-31 14:10 +0200
Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Mike Rapoprt <rppt@linux.vnet.ibm.com> - 2017-05-31 14:30 +0200
Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Vlastimil Babka <vbabka@suse.cz> - 2017-05-24 13:40 +0200
Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Vlastimil Babka <vbabka@suse.cz> - 2017-05-24 17:00 +0200
Re: [PATCH] mm: introduce MADV_CLR_HUGEPAGE Mike Rapoport <rppt@linux.vnet.ibm.com> - 2017-05-24 17:20 +0200
Page 3 of 3 — ← Prev page 1 2 [3]
| From | Mike Rapoport <rppt@linux.vnet.ibm.com> |
|---|---|
| Date | 2017-06-01 10:40 +0200 |
| Message-ID | <tNtOa-cj-15@gated-at.bofh.it> |
| In reply to | #1654900 |
On Thu, Jun 01, 2017 at 10:09:09AM +0200, Michal Hocko wrote: > On Thu 01-06-17 09:53:02, Mike Rapoport wrote: > > On Tue, May 30, 2017 at 04:39:41PM +0200, Michal Hocko wrote: > > > On Tue 30-05-17 16:04:56, Andrea Arcangeli wrote: > > > > > > > > UFFDIO_COPY while not being a major slowdown for sure, it's likely > > > > measurable at the microbenchmark level because it would add a > > > > enter/exit kernel to every 4k memcpy. It's not hard to imagine that as > > > > measurable. How that impacts the total precopy time I don't know, it > > > > would need to be benchmarked to be sure. > > > > > > Yes, please! > > > > I've run a simple test (below) that fills 1G of memory either with memcpy > > of ioctl(UFFDIO_COPY) in 4K chunks. > > The machine I used has two "Intel(R) Xeon(R) CPU E5-2680 0 @ 2.70GHz" and > > 128G of RAM. > > I've averaged elapsed time reported by /usr/bin/time over 100 runs and here > > what I've got: > > > > memcpy with THP on: 0.3278 sec > > memcpy with THP off: 0.5295 sec > > UFFDIO_COPY: 0.44 sec > > I assume that the standard deviation is small? Yes. > > That said, for the CRIU usecase UFFDIO_COPY seems faster that disabling THP > > and then doing memcpy. > > That is a bit surprising. I didn't think that the userfault syscall > (ioctl) can be faster than a regular #PF but considering that > __mcopy_atomic bypasses the page fault path and it can be optimized for > the anon case suggests that we can save some cycles for each page and so > the cumulative savings can be visible. > > -- > Michal Hocko > SUSE Labs >
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| From | Andrea Arcangeli <aarcange@redhat.com> |
|---|---|
| Date | 2017-06-01 15:50 +0200 |
| Message-ID | <tNyEa-3cj-11@gated-at.bofh.it> |
| In reply to | #1654900 |
On Thu, Jun 01, 2017 at 10:09:09AM +0200, Michal Hocko wrote: > That is a bit surprising. I didn't think that the userfault syscall > (ioctl) can be faster than a regular #PF but considering that > __mcopy_atomic bypasses the page fault path and it can be optimized for > the anon case suggests that we can save some cycles for each page and so > the cumulative savings can be visible. __mcopy_atomic works not just for anonymous memory, hugetlbfs/shmem are covered too and there are branches to handle those. If you were to run more than one precopy pass UFFDIO_COPY shall become slower than the userland access starting from the second pass. At the light of this if CRIU can only do one single pass of precopy, CRIU is probably better off using UFFDIO_COPY than using prctl or madvise to temporarily turn off THP. With QEMU as opposed we set MADV_HUGEPAGE during precopy on destination to maximize the THP utilization for all those 2M naturally aligned guest regions that aren't re-dirtied in the source, so we're better off without using UFFDIO_COPY in precopy even during the first pass to avoid the enter/kernel for subpages that are written to destination in a already instantiated THP. At least until we teach QEMU to map 2M at once if possible (UFFDIO_COPY would then also require an enhancement, because currently it won't map THP on the fly). Thanks, Andrea
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| From | Mike Rapoport <rppt@linux.vnet.ibm.com> |
|---|---|
| Date | 2017-06-02 11:20 +0200 |
| Message-ID | <tNQUp-7vd-9@gated-at.bofh.it> |
| In reply to | #1655154 |
On Thu, Jun 01, 2017 at 03:45:22PM +0200, Andrea Arcangeli wrote: > On Thu, Jun 01, 2017 at 10:09:09AM +0200, Michal Hocko wrote: > > That is a bit surprising. I didn't think that the userfault syscall > > (ioctl) can be faster than a regular #PF but considering that > > __mcopy_atomic bypasses the page fault path and it can be optimized for > > the anon case suggests that we can save some cycles for each page and so > > the cumulative savings can be visible. > > __mcopy_atomic works not just for anonymous memory, hugetlbfs/shmem > are covered too and there are branches to handle those. > > If you were to run more than one precopy pass UFFDIO_COPY shall become > slower than the userland access starting from the second pass. > > At the light of this if CRIU can only do one single pass of precopy, > CRIU is probably better off using UFFDIO_COPY than using prctl or > madvise to temporarily turn off THP. CRIU does memory tracking differently from QEMU. Every round of pre-copy in CRIU means we dump the dirty pages into an image file. The restore then chooses what image file to use. Anyway, we fill the memory only once at restore time, hence UFFDIO_COPY would be better than disabling THP. > With QEMU as opposed we set MADV_HUGEPAGE during precopy on > destination to maximize the THP utilization for all those 2M naturally > aligned guest regions that aren't re-dirtied in the source, so we're > better off without using UFFDIO_COPY in precopy even during the first > pass to avoid the enter/kernel for subpages that are written to > destination in a already instantiated THP. At least until we teach > QEMU to map 2M at once if possible (UFFDIO_COPY would then also > require an enhancement, because currently it won't map THP on the > fly). > > Thanks, > Andrea > -- Sincerely yours, Mike.
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| From | Mike Rapoport <rppt@linux.vnet.ibm.com> |
|---|---|
| Date | 2017-05-31 11:10 +0200 |
| Message-ID | <tN7ND-2Od-13@gated-at.bofh.it> |
| In reply to | #1653105 |
On Tue, May 30, 2017 at 12:39:30PM +0200, Michal Hocko wrote: > On Tue 30-05-17 13:19:22, Mike Rapoport wrote: > > > > But then we'll have to populate these regions with > > > > UFFDIO_COPY which adds quite an overhead. > > > > > > How big is the performance impact? > > > > I don't have the numbers handy, but for each post-copy range it means that > > instead of memcpy() we will use ioctl(UFFDIO_COPY). > > It would be good to measure that though. I will, but I won't expect huge difference here. Anyway, memcpy() will touch still unpopulated pages, so we'll anyway enter/exit kernel. > You are proposing a new user > API and the THP api is quite convoluted already so there better be a > very good reason to add a new API. So far I can only see that it would > be more convinient to add another madvise command and that is rather > insufficient justification IMHO. Well, the most convenient for my use case would be simply disable THP before restore and re-enable it afterwards. And the need to use ioctl(UFFDIO_COPY) is not that less convenient that the proposed madvise command. I've proposed the new madvise command because I firmly believe it is missing. All madvise() commands that set some flag in vma->vm_flags have the counter-command that resets that flag. Except for THP. The THP-related flags can define three states for a VMA, pretty much like VM_SEQ_READ and VM_RAND_READ. And it requires three madvise commands to allow setting any of the desired states, just like with MADV_RANDOM, MADV_SEQUENTIAL and MADV_NORMAL. > Also do you expect somebody else would use new madvise? What would be the > usecase? I can think of an application that wants to keep 4K pages to save physical memory for certain phase, e.g. until these pages are populated with very few data. After the memory usage increases, the application may wish to stop preventing khugepged from merging these pages, but it does not have strong inclination to force use of huge pages. > -- > Michal Hocko > SUSE Labs -- Sincerely yours, Mike.
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| From | Michal Hocko <mhocko@kernel.org> |
|---|---|
| Date | 2017-05-31 14:10 +0200 |
| Message-ID | <tNaBR-4zj-33@gated-at.bofh.it> |
| In reply to | #1654025 |
On Wed 31-05-17 12:08:45, Mike Rapoport wrote: > On Tue, May 30, 2017 at 12:39:30PM +0200, Michal Hocko wrote: [...] > > Also do you expect somebody else would use new madvise? What would be the > > usecase? > > I can think of an application that wants to keep 4K pages to save physical > memory for certain phase, e.g. until these pages are populated with very > few data. After the memory usage increases, the application may wish to > stop preventing khugepged from merging these pages, but it does not have > strong inclination to force use of huge pages. Well, is actually anybody going to do that? -- Michal Hocko SUSE Labs
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| From | Mike Rapoprt <rppt@linux.vnet.ibm.com> |
|---|---|
| Date | 2017-05-31 14:30 +0200 |
| Message-ID | <tNaVc-4Fy-5@gated-at.bofh.it> |
| In reply to | #1654169 |
On May 31, 2017 3:05:56 PM GMT+03:00, Michal Hocko <mhocko@kernel.org> wrote: >On Wed 31-05-17 12:08:45, Mike Rapoport wrote: >> On Tue, May 30, 2017 at 12:39:30PM +0200, Michal Hocko wrote: >[...] >> > Also do you expect somebody else would use new madvise? What would >be the >> > usecase? >> >> I can think of an application that wants to keep 4K pages to save >physical >> memory for certain phase, e.g. until these pages are populated with >very >> few data. After the memory usage increases, the application may wish >to >> stop preventing khugepged from merging these pages, but it does not >have >> strong inclination to force use of huge pages. > >Well, is actually anybody going to do that? Well, I don't​ know, it's pretty much future telling :) For sure, without the new madvise nobody will be even able to do that.
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| From | Vlastimil Babka <vbabka@suse.cz> |
|---|---|
| Date | 2017-05-24 13:40 +0200 |
| Message-ID | <tKCNY-1KT-23@gated-at.bofh.it> |
| In reply to | #1649455 |
On 05/24/2017 12:39 PM, Mike Rapoport wrote: >> Hm so the prctl does: >> >> if (arg2) >> me->mm->def_flags |= VM_NOHUGEPAGE; >> else >> me->mm->def_flags &= ~VM_NOHUGEPAGE; >> >> That's rather lazy implementation IMHO. Could we change it so the flag >> is stored elsewhere in the mm, and the code that decides to (not) use >> THP will check both the per-vma flag and the per-mm flag? > > I afraid I don't understand how that can help. > What we need is an ability to temporarily disable collapse of the pages in > VMAs that do not have VM_*HUGEPAGE flags set and that after we re-enable > THP, the vma->vm_flags for those VMAs will remain intact. That's what I'm saying - instead of implementing the prctl flag via mm->def_flags (which gets permanently propagated to newly created vma's but e.g. doesn't affect already existing ones), it would be setting a flag somewhere in mm, which khugepaged (and page faults) would check in addition to the per-vma flags. > -- > Sincerely yours, > Mike. > > -- > 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> >
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| From | Vlastimil Babka <vbabka@suse.cz> |
|---|---|
| Date | 2017-05-24 17:00 +0200 |
| Message-ID | <tKFVv-3Cg-5@gated-at.bofh.it> |
| In reply to | #1649510 |
On 05/24/2017 04:28 PM, Pavel Emelyanov wrote: > On 05/24/2017 02:31 PM, Vlastimil Babka wrote: >> On 05/24/2017 12:39 PM, Mike Rapoport wrote: >>>> Hm so the prctl does: >>>> >>>> if (arg2) >>>> me->mm->def_flags |= VM_NOHUGEPAGE; >>>> else >>>> me->mm->def_flags &= ~VM_NOHUGEPAGE; >>>> >>>> That's rather lazy implementation IMHO. Could we change it so the flag >>>> is stored elsewhere in the mm, and the code that decides to (not) use >>>> THP will check both the per-vma flag and the per-mm flag? >>> >>> I afraid I don't understand how that can help. >>> What we need is an ability to temporarily disable collapse of the pages in >>> VMAs that do not have VM_*HUGEPAGE flags set and that after we re-enable >>> THP, the vma->vm_flags for those VMAs will remain intact. >> >> That's what I'm saying - instead of implementing the prctl flag via >> mm->def_flags (which gets permanently propagated to newly created vma's >> but e.g. doesn't affect already existing ones), it would be setting a >> flag somewhere in mm, which khugepaged (and page faults) would check in >> addition to the per-vma flags. > > I do not insist, but this would make existing paths (checking for flags) be > 2 times slower -- from now on these would need to check two bits (vma flags > and mm flags) which are 100% in different cache lines. I'd expect you already have mm struct cached during a page fault. And THP-eligible page fault is just one per pmd, the overhead should be practically zero. > What Mike is proposing is the way to fine-tune the existing vma flags. This > would keep current paths as fast (or slow ;) ) as they are now. All the > complexity would go to rare cases when someone needs to turn thp off for a > while and then turn it back on. Yeah but it's extending user-space API for a corner case. We should do that only when there's no other option. > -- Pavel > > -- > 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> >
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| From | Mike Rapoport <rppt@linux.vnet.ibm.com> |
|---|---|
| Date | 2017-05-24 17:20 +0200 |
| Message-ID | <tKGeS-40h-15@gated-at.bofh.it> |
| In reply to | #1649691 |
On Wed, May 24, 2017 at 04:54:38PM +0200, Vlastimil Babka wrote: > On 05/24/2017 04:28 PM, Pavel Emelyanov wrote: > > On 05/24/2017 02:31 PM, Vlastimil Babka wrote: > >> On 05/24/2017 12:39 PM, Mike Rapoport wrote: > >>>> Hm so the prctl does: > >>>> > >>>> if (arg2) > >>>> me->mm->def_flags |= VM_NOHUGEPAGE; > >>>> else > >>>> me->mm->def_flags &= ~VM_NOHUGEPAGE; > >>>> > >>>> That's rather lazy implementation IMHO. Could we change it so the flag > >>>> is stored elsewhere in the mm, and the code that decides to (not) use > >>>> THP will check both the per-vma flag and the per-mm flag? > >>> > >>> I afraid I don't understand how that can help. > >>> What we need is an ability to temporarily disable collapse of the pages in > >>> VMAs that do not have VM_*HUGEPAGE flags set and that after we re-enable > >>> THP, the vma->vm_flags for those VMAs will remain intact. > >> > >> That's what I'm saying - instead of implementing the prctl flag via > >> mm->def_flags (which gets permanently propagated to newly created vma's > >> but e.g. doesn't affect already existing ones), it would be setting a > >> flag somewhere in mm, which khugepaged (and page faults) would check in > >> addition to the per-vma flags. > > > > I do not insist, but this would make existing paths (checking for flags) be > > 2 times slower -- from now on these would need to check two bits (vma flags > > and mm flags) which are 100% in different cache lines. > > I'd expect you already have mm struct cached during a page fault. And > THP-eligible page fault is just one per pmd, the overhead should be > practically zero. > > > What Mike is proposing is the way to fine-tune the existing vma flags. This > > would keep current paths as fast (or slow ;) ) as they are now. All the > > complexity would go to rare cases when someone needs to turn thp off for a > > while and then turn it back on. > > Yeah but it's extending user-space API for a corner case. We should do > that only when there's no other option. With madvise() I'm suggesting we rather add "completeness" to the existing API, IMHO. We do have API that sets VM_HUGEPAGE and clears VM_NOHUGEPAGE or vise versa, but we do not have an API that can clear both flags... And if we would use prctl(), we either change user visible behaviour or we still need to extend the API and use, say, arg2 to distinguish between the current behaviour and the new one. -- Sincerely yours, Mike.
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