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Message-ID: <CAJD7tkY+2_WJ4U+6-Jju729r9OKF36AANzT4WnSQnm8+bz2=hw@mail.gmail.com> Date: Tue, 24 Sep 2024 12:34:47 -0700 From: Yosry Ahmed <yosryahmed@...gle.com> To: Kanchana P Sridhar <kanchana.p.sridhar@...el.com> Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org, hannes@...xchg.org, nphamcs@...il.com, chengming.zhou@...ux.dev, usamaarif642@...il.com, shakeel.butt@...ux.dev, ryan.roberts@....com, ying.huang@...el.com, 21cnbao@...il.com, akpm@...ux-foundation.org, nanhai.zou@...el.com, wajdi.k.feghali@...el.com, vinodh.gopal@...el.com Subject: Re: [PATCH v7 0/8] mm: ZSWAP swap-out of mTHP folios On Mon, Sep 23, 2024 at 6:17 PM Kanchana P Sridhar <kanchana.p.sridhar@...el.com> wrote: > > Hi All, > > This patch-series enables zswap_store() to accept and store mTHP > folios. The most significant contribution in this series is from the > earlier RFC submitted by Ryan Roberts [1]. Ryan's original RFC has been > migrated to mm-unstable as of 9-23-2024 in patches 5,6 of this series. > > [1]: [RFC PATCH v1] mm: zswap: Store large folios without splitting > https://lore.kernel.org/linux-mm/20231019110543.3284654-1-ryan.roberts@arm.com/T/#u > > Additionally, there is an attempt to modularize some of the functionality > in zswap_store(), to make it more amenable to supporting any-order > mTHPs. For instance, the function zswap_store_entry() stores a zswap_entry > in the xarray. Likewise, zswap_delete_stored_offsets() can be used to > delete all offsets corresponding to a higher order folio stored in zswap. These are implementation details that are not very useful here, you can just mention that the first few patches do refactoring prep work. > > For accounting purposes, the patch-series adds per-order mTHP sysfs > "zswpout" counters that get incremented upon successful zswap_store of > an mTHP folio: > > /sys/kernel/mm/transparent_hugepage/hugepages-*kB/stats/zswpout > > A new config variable CONFIG_ZSWAP_STORE_THP_DEFAULT_ON (off by default) > will enable/disable zswap storing of (m)THP. When disabled, zswap will > fallback to rejecting the mTHP folio, to be processed by the backing > swap device. Why is this needed? Do we just not have enough confidence in the feature yet, or are there some cases that regress from enabling mTHP for zswapout? Does generic mTHP swapout/swapin also use config options? > > This patch-series is a pre-requisite for ZSWAP compress batching of mTHP > swap-out and decompress batching of swap-ins based on swapin_readahead(), > using Intel IAA hardware acceleration, which we would like to submit in > subsequent patch-series, with performance improvement data. > > Thanks to Ying Huang for pre-posting review feedback and suggestions! > > Thanks also to Nhat, Yosry, Barry, Chengming, Usama and Ying for their > helpful feedback, data reviews and suggestions! > > Co-development signoff request: > =============================== > I would like to request Ryan Roberts' co-developer signoff on patches > 5 and 6 in this series. Thanks Ryan! > > Changes since v6: > ================= Please put the changelog at the very end, I almost missed the performance evaluation. > 1) Rebased to mm-unstable as of 9-23-2024, > commit acfabf7e197f7a5bedf4749dac1f39551417b049. > 2) Refactored into smaller commits, as suggested by Yosry and > Chengming. Thanks both! > 3) Reworded the commit log for patches 5 and 6 as per Yosry's > suggestion. Thanks Yosry! > 4) Gathered data on a Sapphire Rapids server that has 823GiB SSD swap disk > partition. Also, all experiments are run with usemem --sleep 10, so that > the memory allocated by the 70 processes remains in memory > longer. Posted elapsed and sys times. Thanks to Yosry, Nhat and Ying for > their help with refining the performance characterization methodology. > 5) Updated Documentation/admin-guide/mm/transhuge.rst as suggested by > Nhat. Thanks Nhat! > > Changes since v5: > ================= > 1) Rebased to mm-unstable as of 8/29/2024, > commit 9287e4adbc6ab8fa04d25eb82e097fed877a4642. > 2) Added CONFIG_ZSWAP_STORE_THP_DEFAULT_ON (off by default) to > enable/disable zswap_store() of mTHP folios. Thanks Nhat for the > suggestion to add a knob by which users can enable/disable this > change. Nhat, I hope this is along the lines of what you were > thinking. > 3) Added vm-scalability usemem data with 4K folios with > CONFIG_ZSWAP_STORE_THP_DEFAULT_ON off, that I gathered to make sure > there is no regression with this change. > 4) Added data with usemem with 64K and 2M THP for an alternate view of > before/after, as suggested by Yosry, so we can understand the impact > of when mTHPs are split into 4K folios in shrink_folio_list() > (CONFIG_THP_SWAP off) vs. not split (CONFIG_THP_SWAP on) and stored > in zswap. Thanks Yosry for this suggestion. > > Changes since v4: > ================= > 1) Published before/after data with zstd, as suggested by Nhat (Thanks > Nhat for the data reviews!). > 2) Rebased to mm-unstable from 8/27/2024, > commit b659edec079c90012cf8d05624e312d1062b8b87. > 3) Incorporated the change in memcontrol.h that defines obj_cgroup_get() if > CONFIG_MEMCG is not defined, to resolve build errors reported by kernel > robot; as per Nhat's and Michal's suggestion to not require a separate > patch to fix the build errors (thanks both!). > 4) Deleted all same-filled folio processing in zswap_store() of mTHP, as > suggested by Yosry (Thanks Yosry!). > 5) Squashed the commits that define new mthp zswpout stat counters, and > invoke count_mthp_stat() after successful zswap_store()s; into a single > commit. Thanks Yosry for this suggestion! > > Changes since v3: > ================= > 1) Rebased to mm-unstable commit 8c0b4f7b65fd1ca7af01267f491e815a40d77444. > Thanks to Barry for suggesting aligning with Ryan Roberts' latest > changes to count_mthp_stat() so that it's always defined, even when THP > is disabled. Barry, I have also made one other change in page_io.c > where count_mthp_stat() is called by count_swpout_vm_event(). I would > appreciate it if you can review this. Thanks! > Hopefully this should resolve the kernel robot build errors. > > Changes since v2: > ================= > 1) Gathered usemem data using SSD as the backing swap device for zswap, > as suggested by Ying Huang. Ying, I would appreciate it if you can > review the latest data. Thanks! > 2) Generated the base commit info in the patches to attempt to address > the kernel test robot build errors. > 3) No code changes to the individual patches themselves. > > Changes since RFC v1: > ===================== > > 1) Use sysfs for zswpout mTHP stats, as per Barry Song's suggestion. > Thanks Barry! > 2) Addressed some of the code review comments that Nhat Pham provided in > Ryan's initial RFC [1]: > - Added a comment about the cgroup zswap limit checks occuring once per > folio at the beginning of zswap_store(). > Nhat, Ryan, please do let me know if the comments convey the summary > from the RFC discussion. Thanks! > - Posted data on running the cgroup suite's zswap kselftest. > 3) Rebased to v6.11-rc3. > 4) Gathered performance data with usemem and the rebased patch-series. > > > Regression Testing: > =================== > I ran vm-scalability usemem 70 processes without mTHP, i.e., only 4K > folios with mm-unstable and with this patch-series. The main goal was > to make sure that there is no functional or performance regression > wrt the earlier zswap behavior for 4K folios, > CONFIG_ZSWAP_STORE_THP_DEFAULT_ON is not set, and zswap_store() of 4K > pages goes through the newly added code path [zswap_store(), > zswap_store_page()]. > > The data indicates there is no regression. > > ------------------------------------------------------------------------------ > mm-unstable 8-28-2024 zswap-mTHP v6 > CONFIG_ZSWAP_STORE_THP_DEFAULT_ON > is not set > ------------------------------------------------------------------------------ > ZSWAP compressor zstd deflate- zstd deflate- > iaa iaa > ------------------------------------------------------------------------------ > Throughput (KB/s) 110,775 113,010 111,550 121,937 > sys time (sec) 1,141.72 954.87 1,131.95 828.47 > memcg_high 140,500 153,737 139,772 134,129 > memcg_swap_high 0 0 0 0 > memcg_swap_fail 0 0 0 0 > pswpin 0 0 0 0 > pswpout 0 0 0 0 > zswpin 675 690 682 684 > zswpout 9,552,298 10,603,271 9,566,392 9,267,213 > thp_swpout 0 0 0 0 > thp_swpout_ 0 0 0 0 > fallback > pgmajfault 3,453 3,468 3,841 3,487 > ZSWPOUT-64kB-mTHP n/a n/a 0 0 > SWPOUT-64kB-mTHP 0 0 0 0 > ------------------------------------------------------------------------------ It's probably better to put the zstd columns next to each other, and the deflate-iaa columns next to each other, for easier visual comparisons. > > > Performance Testing: > ==================== > Testing of this patch-series was done with mm-unstable as of 9-23-2024, > commit acfabf7e197f7a5bedf4749dac1f39551417b049. Data was gathered > without/with this patch-series, on an Intel Sapphire Rapids server, > dual-socket 56 cores per socket, 4 IAA devices per socket, 503 GiB RAM and > 823G SSD disk partition swap. Core frequency was fixed at 2500MHz. > > The vm-scalability "usemem" test was run in a cgroup whose memory.high > was fixed at 40G. The is no swap limit set for the cgroup. Following a > similar methodology as in Ryan Roberts' "Swap-out mTHP without splitting" > series [2], 70 usemem processes were run, each allocating and writing 1G of > memory, and sleeping for 10 sec before exiting: > > usemem --init-time -w -O -s 10 -n 70 1g > > The vm/sysfs mTHP stats included with the performance data provide details > on the swapout activity to ZSWAP/swap. > > Other kernel configuration parameters: > > ZSWAP Compressors : zstd, deflate-iaa > ZSWAP Allocator : zsmalloc > SWAP page-cluster : 2 > > In the experiments where "deflate-iaa" is used as the ZSWAP compressor, > IAA "compression verification" is enabled. Hence each IAA compression > will be decompressed internally by the "iaa_crypto" driver, the crc-s > returned by the hardware will be compared and errors reported in case of > mismatches. Thus "deflate-iaa" helps ensure better data integrity as > compared to the software compressors. > > Throughput is derived by averaging the individual 70 processes' throughputs > reported by usemem. elapsed/sys times are measured with perf. All data > points per compressor/kernel/mTHP configuration are averaged across 3 runs. > > Case 1: Comparing zswap 4K vs. zswap mTHP > ========================================= > > In this scenario, the "before" is CONFIG_THP_SWAP set to off, that results in > 64K/2M (m)THP to be split into 4K folios that get processed by zswap. > > The "after" is CONFIG_THP_SWAP set to on, and this patch-series, that results > in 64K/2M (m)THP to not be split, and processed by zswap. > > 64KB mTHP (cgroup memory.high set to 40G): > ========================================== > > ------------------------------------------------------------------------------- > mm-unstable 9-23-2024 zswap-mTHP Change wrt > CONFIG_THP_SWAP=N CONFIG_THP_SWAP=Y Baseline > Baseline > ------------------------------------------------------------------------------- > ZSWAP compressor zstd deflate- zstd deflate- zstd deflate- > iaa iaa iaa > ------------------------------------------------------------------------------- > Throughput (KB/s) 143,323 125,485 153,550 129,609 7% 3% > elapsed time (sec) 24.97 25.42 23.90 25.19 4% 1% > sys time (sec) 822.72 750.96 757.70 731.13 8% 3% > memcg_high 132,743 169,825 148,075 192,744 > memcg_swap_fail 639,067 841,553 2,204 2,215 > pswpin 0 0 0 0 > pswpout 0 0 0 0 > zswpin 795 873 760 902 > zswpout 10,011,266 13,195,137 10,010,017 13,193,554 > thp_swpout 0 0 0 0 > thp_swpout_ 0 0 0 0 > fallback > 64kB-mthp_ 639,065 841,553 2,204 2,215 > swpout_fallback > pgmajfault 2,861 2,924 3,054 3,259 > ZSWPOUT-64kB n/a n/a 623,451 822,268 > SWPOUT-64kB 0 0 0 0 > ------------------------------------------------------------------------------- > > > 2MB PMD-THP/2048K mTHP (cgroup memory.high set to 40G): > ======================================================= > > ------------------------------------------------------------------------------- > mm-unstable 9-23-2024 zswap-mTHP Change wrt > CONFIG_THP_SWAP=N CONFIG_THP_SWAP=Y Baseline > Baseline > ------------------------------------------------------------------------------- > ZSWAP compressor zstd deflate- zstd deflate- zstd deflate- > iaa iaa iaa > ------------------------------------------------------------------------------- > Throughput (KB/s) 145,616 139,640 169,404 141,168 16% 1% > elapsed time (sec) 25.05 23.85 23.02 23.37 8% 2% > sys time (sec) 790.53 676.34 613.26 677.83 22% -0.2% > memcg_high 16,702 25,197 17,374 23,890 > memcg_swap_fail 21,485 27,814 114 144 > pswpin 0 0 0 0 > pswpout 0 0 0 0 > zswpin 793 852 778 922 > zswpout 10,011,709 13,186,882 10,010,893 13,195,600 > thp_swpout 0 0 0 0 > thp_swpout_ 21,485 27,814 114 144 > fallback > 2048kB-mthp_ n/a n/a 0 0 > swpout_fallback > pgmajfault 2,701 2,822 4,151 5,066 > ZSWPOUT-2048kB n/a n/a 19,442 25,615 > SWPOUT-2048kB 0 0 0 0 > ------------------------------------------------------------------------------- > > We mostly see improvements in throughput, elapsed and sys time for zstd and > deflate-iaa, when comparing before (THP_SWAP=N) vs. after (THP_SWAP=Y). > > > Case 2: Comparing SSD swap mTHP vs. zswap mTHP > ============================================== > > In this scenario, CONFIG_THP_SWAP is enabled in "before" and "after" > experiments. The "before" represents zswap rejecting mTHP, and the mTHP > being stored by the 823G SSD swap. The "after" represents data with this > patch-series, that results in 64K/2M (m)THP being processed and stored by > zswap. > > 64KB mTHP (cgroup memory.high set to 40G): > ========================================== > > ------------------------------------------------------------------------------- > mm-unstable 9-23-2024 zswap-mTHP Change wrt > CONFIG_THP_SWAP=Y CONFIG_THP_SWAP=Y Baseline > Baseline > ------------------------------------------------------------------------------- > ZSWAP compressor zstd deflate- zstd deflate- zstd deflate- > iaa iaa iaa > ------------------------------------------------------------------------------- > Throughput (KB/s) 20,265 20,696 153,550 129,609 658% 526% > elapsed time (sec) 72.44 70.86 23.90 25.19 67% 64% > sys time (sec) 77.95 77.99 757.70 731.13 -872% -837% > memcg_high 115,811 113,277 148,075 192,744 > memcg_swap_fail 2,386 2,425 2,204 2,215 > pswpin 16 16 0 0 > pswpout 7,774,235 7,616,069 0 0 > zswpin 728 749 760 902 > zswpout 38,424 39,022 10,010,017 13,193,554 > thp_swpout 0 0 0 0 > thp_swpout_ 0 0 0 0 > fallback > 64kB-mthp_ 2,386 2,425 2,204 2,215 > swpout_fallback > pgmajfault 2,757 2,860 3,054 3,259 > ZSWPOUT-64kB n/a n/a 623,451 822,268 > SWPOUT-64kB 485,890 476,004 0 0 > ------------------------------------------------------------------------------- > > > 2MB PMD-THP/2048K mTHP (cgroup memory.high set to 40G): > ======================================================= > > ------------------------------------------------------------------------------- > mm-unstable 9-23-2024 zswap-mTHP Change wrt > CONFIG_THP_SWAP=Y CONFIG_THP_SWAP=Y Baseline > Baseline > ------------------------------------------------------------------------------- > ZSWAP compressor zstd deflate- zstd deflate- zstd deflate- > iaa iaa iaa > ------------------------------------------------------------------------------- > Throughput (KB/s) 24,347 35,971 169,404 141,168 596% 292% > elapsed time (sec) 63.52 64.59 23.02 23.37 64% 64% > sys time (sec) 27.91 27.01 613.26 677.83 -2098% -2410% > memcg_high 13,576 13,467 17,374 23,890 > memcg_swap_fail 162 124 114 144 > pswpin 0 0 0 0 > pswpout 7,003,307 7,168,853 0 0 > zswpin 741 722 778 922 > zswpout 84,429 65,315 10,010,893 13,195,600 > thp_swpout 13,678 14,002 0 0 > thp_swpout_ 162 124 114 144 > fallback > 2048kB-mthp_ n/a n/a 0 0 > swpout_fallback > pgmajfault 3,345 2,903 4,151 5,066 > ZSWPOUT-2048kB n/a n/a 19,442 25,615 > SWPOUT-2048kB 13,678 14,002 0 0 > ------------------------------------------------------------------------------- > > We see significant improvements in throughput and elapsed time for zstd and > deflate-iaa, when comparing before (mTHP-SSD) vs. after (mTHP-ZSWAP). The > sys time increases with mTHP-ZSWAP as expected, due to the CPU compression > time vs. asynchronous disk write times, as pointed out by Ying and Yosry. > > In the "Before" scenario, when zswap does not store mTHP, only allocations > count towards the cgroup memory limit. However, in the "After" scenario, > with the introduction of zswap_store() mTHP, both, allocations as well as > the zswap compressed pool usage from all 70 processes are counted towards > the memory limit. As a result, we see higher swapout activity in the > "After" data. Hence, more time is spent doing reclaim as the zswap cgroup > charge leads to more frequent memory.high breaches. > > Summary: > ======== > The v7 data presented above comparing zswap-mTHP with a conventional 823G > SSD swap demonstrates good performance improvements with zswap-mTHP. Hence, > it seems reasonable for zswap_store to support (m)THP, so that further > performance improvements can be implemented. > > Some of the ideas that have shown promise in our experiments are: > > 1) IAA compress/decompress batching. > 2) Distributing compress jobs across all IAA devices on the socket. > > In the experimental setup used in this patchset, we have enabled > IAA compress verification to ensure additional hardware data integrity CRC > checks not currently done by the software compressors. The tests run for > this patchset are also using only 1 IAA device per core, that avails of 2 > compress engines on the device. In our experiments with IAA batching, we > distribute compress jobs from all cores to the 8 compress engines available > per socket. We further compress the pages in each mTHP in parallel in the > accelerator. As a result, we improve compress latency and reclaim > throughput. > > The following compares the same usemem workload characteristics between: > > 1) zstd (v7 experiments) > 2) deflate-iaa "Fixed mode" (v7 experiments) > 3) deflate-iaa with batching > 4) deflate-iaa-canned "Canned mode" [3] with batching > > vm.page-cluster is set to "2" for all runs. > > 64K mTHP ZSWAP: > =============== > > ------------------------------------------------------------------------------- > ZSWAP zstd IAA Fixed IAA Fixed IAA Canned IAA IAA IAA > compressor (v7) (v7) + Batching + Batching Batch Canned Canned > vs. vs. Batch > 64K mTHP Seqtl Fixed vs. > ZSTD > ------------------------------------------------------------------------------- > Throughput 153,550 129,609 156,215 166,975 21% 7% 9% > (KB/s) > elapsed time 23.90 25.19 22.46 21.38 11% 5% 11% > (sec) > sys time 757.70 731.13 715.62 648.83 2% 9% 14% > (sec) > memcg_high 148,075 192,744 197,548 181,734 > memcg_swap_ 2,204 2,215 2,293 2,263 > fail > pswpin 0 0 0 0 > pswpout 0 0 0 0 > zswpin 760 902 774 833 > zswpout 10,010,017 13,193,554 13,193,176 12,125,616 > thp_swpout 0 0 0 0 > thp_swpout_ 0 0 0 0 > fallback > 64kB-mthp_ 2,204 2,215 2,293 2,263 > swpout_ > fallback > pgmajfault 3,054 3,259 3,545 3,516 > ZSWPOUT-64kB 623,451 822,268 822,176 755,480 > SWPOUT-64kB 0 0 0 0 > swap_ra 146 161 152 159 > swap_ra_hit 64 121 68 88 > ------------------------------------------------------------------------------- > > > 2M THP ZSWAP: > ============= > > ------------------------------------------------------------------------------- > ZSWAP zstd IAA Fixed IAA Fixed IAA Canned IAA IAA IAA > compressor (v7) (v7) + Batching + Batching Batch Canned Canned > vs. vs. Batch > 2M THP Seqtl Fixed vs. > ZSTD > ------------------------------------------------------------------------------- > Throughput 169,404 141,168 175,089 193,407 24% 10% 14% > (KB/s) > elapsed time 23.02 23.37 21.13 19.97 10% 5% 13% > (sec) > sys time 613.26 677.83 630.51 533.80 7% 15% 13% > (sec) > memcg_high 17,374 23,890 24,349 22,374 > memcg_swap_ 114 144 102 88 > fail > pswpin 0 0 0 0 > pswpout 0 0 0 0 > zswpin 778 922 6,492 6,642 > zswpout 10,010,893 13,195,600 13,199,907 12,132,265 > thp_swpout 0 0 0 0 > thp_swpout_ 114 144 102 88 > fallback > pgmajfault 4,151 5,066 5,032 4,999 > ZSWPOUT-2MB 19,442 25,615 25,666 23,594 > SWPOUT-2MB 0 0 0 0 > swap_ra 3 9 4,383 4,494 > swap_ra_hit 2 6 4,298 4,412 > ------------------------------------------------------------------------------- > > > With ZSWAP IAA compress/decompress batching, we are able to demonstrate > significant performance improvements and memory savings in scalability > experiments under memory pressure, as compared to software compressors. We > hope to submit this work in subsequent patch series. Honestly I would remove the detailed results of the followup series for batching, it should be enough to mention a single figure for further expected improvement from ongoing work that depends on this. > > Thanks, > Kanchana > > [1] https://lore.kernel.org/linux-mm/20231019110543.3284654-1-ryan.roberts@arm.com/T/#u > [2] https://lore.kernel.org/linux-mm/20240408183946.2991168-1-ryan.roberts@arm.com/ > [3] https://patchwork.kernel.org/project/linux-crypto/cover/cover.1710969449.git.andre.glover@linux.intel.com/ > > > Kanchana P Sridhar (8): > mm: Define obj_cgroup_get() if CONFIG_MEMCG is not defined. > mm: zswap: Modify zswap_compress() to accept a page instead of a > folio. > mm: zswap: Refactor code to store an entry in zswap xarray. > mm: zswap: Refactor code to delete stored offsets in case of errors. > mm: zswap: Compress and store a specific page in a folio. > mm: zswap: Support mTHP swapout in zswap_store(). > mm: swap: Count successful mTHP ZSWAP stores in sysfs mTHP zswpout > stats. > mm: Document the newly added mTHP zswpout stats, clarify swpout > semantics. > > Documentation/admin-guide/mm/transhuge.rst | 8 +- > include/linux/huge_mm.h | 1 + > include/linux/memcontrol.h | 4 + > mm/Kconfig | 8 + > mm/huge_memory.c | 3 + > mm/page_io.c | 1 + > mm/zswap.c | 248 ++++++++++++++++----- > 7 files changed, 210 insertions(+), 63 deletions(-) > > > base-commit: acfabf7e197f7a5bedf4749dac1f39551417b049 > -- > 2.27.0 >
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