Messages in this thread | ![/](/images/icornerl.gif) | | Date | Wed, 5 Jul 2023 21:38:33 +0200 | Subject | Re: [PATCH v2 0/5] variable-order, large folios for anonymous memory | From | David Hildenbrand <> |
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On 03.07.23 15:53, Ryan Roberts wrote: > Hi All, > > This is v2 of a series to implement variable order, large folios for anonymous > memory. The objective of this is to improve performance by allocating larger > chunks of memory during anonymous page faults. See [1] for background. > > I've significantly reworked and simplified the patch set based on comments from > Yu Zhao (thanks for all your feedback!). I've also renamed the feature to > VARIABLE_THP, on Yu's advice. > > The last patch is for arm64 to explicitly override the default > arch_wants_pte_order() and is intended as an example. If this series is accepted > I suggest taking the first 4 patches through the mm tree and the arm64 change > could be handled through the arm64 tree separately. Neither has any build > dependency on the other. > > The one area where I haven't followed Yu's advice is in the determination of the > size of folio to use. It was suggested that I have a single preferred large > order, and if it doesn't fit in the VMA (due to exceeding VMA bounds, or there > being existing overlapping populated PTEs, etc) then fallback immediately to > order-0. It turned out that this approach caused a performance regression in the > Speedometer benchmark. With my v1 patch, there were significant quantities of > memory which could not be placed in the 64K bucket and were instead being > allocated for the 32K and 16K buckets. With the proposed simplification, that > memory ended up using the 4K bucket, so page faults increased by 2.75x compared > to the v1 patch (although due to the 64K bucket, this number is still a bit > lower than the baseline). So instead, I continue to calculate a folio order that > is somewhere between the preferred order and 0. (See below for more details). > > The patches are based on top of v6.4 plus Matthew Wilcox's set_ptes() series > [2], which is a hard dependency. I have a branch at [3]. > > > Changes since v1 [1] > -------------------- > > - removed changes to arch-dependent vma_alloc_zeroed_movable_folio() > - replaced with arch-independent alloc_anon_folio() > - follows THP allocation approach > - no longer retry with intermediate orders if allocation fails > - fallback directly to order-0 > - remove folio_add_new_anon_rmap_range() patch > - instead add its new functionality to folio_add_new_anon_rmap() > - remove batch-zap pte mappings optimization patch > - remove enabler folio_remove_rmap_range() patch too > - These offer real perf improvement so will submit separately > - simplify Kconfig > - single FLEXIBLE_THP option, which is independent of arch > - depends on TRANSPARENT_HUGEPAGE > - when enabled default to max anon folio size of 64K unless arch > explicitly overrides > - simplify changes to do_anonymous_page(): > - no more retry loop > > > Performance > ----------- > > Below results show 3 benchmarks; kernel compilation with 8 jobs, kernel > compilation with 80 jobs, and speedometer 2.0 (a javascript benchmark running in > Chromium). All cases are running on Ampere Altra with 1 NUMA node enabled, > Ubuntu 22.04 and XFS filesystem. Each benchmark is repeated 15 times over 5 > reboots and averaged. > > 'anonfolio-lkml-v1' is the v1 patchset at [1]. 'anonfolio-lkml-v2' is this v2 > patchset. 'anonfolio-lkml-v2-simple-order' is anonfolio-lkml-v2 but with the > order selection simplification that Yu Zhao suggested - I'm trying to justify > here why I did not follow the advice. > > > Kernel compilation with 8 jobs: > > | kernel | real-time | kern-time | user-time | > |:-------------------------------|------------:|------------:|------------:| > | baseline-4k | 0.0% | 0.0% | 0.0% | > | anonfolio-lkml-v1 | -5.3% | -42.9% | -0.6% | > | anonfolio-lkml-v2-simple-order | -4.4% | -36.5% | -0.4% | > | anonfolio-lkml-v2 | -4.8% | -38.6% | -0.6% | > > We can see that the simple-order approach is responsible for a regression of > 0.4%. > > > Kernel compilation with 80 jobs: > > | kernel | real-time | kern-time | user-time | > |:-------------------------------|------------:|------------:|------------:| > | baseline-4k | 0.0% | 0.0% | 0.0% | > | anonfolio-lkml-v1 | -4.6% | -45.7% | 1.4% | > | anonfolio-lkml-v2-simple-order | -4.7% | -40.2% | -0.1% | > | anonfolio-lkml-v2 | -5.0% | -42.6% | -0.3% | > > simple-order costs 0.3 % here. v2 is actually performing higher than v1 due to > fixing the v1 regression on user-time. > > > Speedometer 2.0: > > | kernel | runs_per_min | > |:-------------------------------|---------------:| > | baseline-4k | 0.0% | > | anonfolio-lkml-v1 | 0.7% | > | anonfolio-lkml-v2-simple-order | -0.9% | > | anonfolio-lkml-v2 | 0.5% | > > simple-order regresses performance by 0.9% vs the baseline, for a total negative > swing of 1.6% vs v1. This is fixed by keeping the more complex order selection > mechanism from v1. > > > The remaining (kernel time) performance gap between v1 and v2 for the above > benchmarks is due to the removal of the "batch zap" patch in v2. Adding that > back in gives us the performance back. I intend to submit that as a separate > series once this series is accepted. > > > [1] https://lore.kernel.org/linux-mm/20230626171430.3167004-1-ryan.roberts@arm.com/ > [2] https://lore.kernel.org/linux-mm/20230315051444.3229621-1-willy@infradead.org/ > [3] https://gitlab.arm.com/linux-arm/linux-rr/-/tree/features/granule_perf/anonfolio-lkml_v2 > > Thanks, > Ryan
Hi Ryan,
is page migration already working as expected (what about page compaction?), and do we handle migration -ENOMEM when allocating a target page: do we split an fallback to 4k page migration?
-- Cheers,
David / dhildenb
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