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Message-ID: <875xrigy21.fsf@yhuang6-desk2.ccr.corp.intel.com> Date: Fri, 30 Aug 2024 17:27:50 +0800 From: "Huang, Ying" <ying.huang@...el.com> To: Yosry Ahmed <yosryahmed@...gle.com> Cc: Kanchana P Sridhar <kanchana.p.sridhar@...el.com>, linux-kernel@...r.kernel.org, linux-mm@...ck.org, hannes@...xchg.org, nphamcs@...il.com, chengming.zhou@...ux.dev, usamaarif642@...il.com, ryan.roberts@....com, 21cnbao@...il.com, akpm@...ux-foundation.org, nanhai.zou@...el.com, wajdi.k.feghali@...el.com, vinodh.gopal@...el.com Subject: Re: [PATCH v6 0/3] mm: ZSWAP swap-out of mTHP folios Yosry Ahmed <yosryahmed@...gle.com> writes: > On Thu, Aug 29, 2024 at 2:27 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 v6.11-rc3 in patch 2/4 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. >> >> 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. >> >> This patch-series is a precursor to 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 RFC patch-series, with performance improvement data. >> >> Thanks to Ying Huang for pre-posting review feedback and suggestions! >> >> Thanks also to Nhat, Yosry and Barry for their helpful feedback, data >> reviews and suggestions! >> >> 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 >> ------------------------------------------------------------------------------ >> >> >> Performance Testing: >> ==================== >> Testing of this patch-series was done with the v6.11-rc3 mainline, without >> and with this patch-series, on an Intel Sapphire Rapids server, >> dual-socket 56 cores per socket, 4 IAA devices per socket. >> >> The system has 503 GiB RAM, with 176GiB ZRAM (35% of available RAM) as the >> backing swap device for ZSWAP. zstd is configured as the ZRAM compressor. >> 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: >> >> usemem --init-time -w -O -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. sys time is measured with perf. All data points are >> averaged across 3 runs. >> >> Case 1: Baseline with CONFIG_THP_SWAP turned off, and mTHP is split in reclaim. >> =============================================================================== >> >> In this scenario, the "before" is CONFIG_THP_SWAP set to off, that results in >> 64K/2M (m)THP to be split, and only 4K folios 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): >> ========================================== >> >> ------------------------------------------------------------------------------- >> v6.11-rc3 mainline zswap-mTHP Change wrt >> Baseline Baseline >> CONFIG_THP_SWAP=N CONFIG_THP_SWAP=Y >> ------------------------------------------------------------------------------- >> ZSWAP compressor zstd deflate- zstd deflate- zstd deflate- >> iaa iaa iaa >> ------------------------------------------------------------------------------- >> Throughput (KB/s) 136,113 140,044 140,363 151,938 3% 8% >> sys time (sec) 986.78 951.95 954.85 735.47 3% 23% >> memcg_high 124,183 127,513 138,651 133,884 >> memcg_swap_high 0 0 0 0 >> memcg_swap_fail 619,020 751,099 0 0 >> pswpin 0 0 0 0 >> pswpout 0 0 0 0 >> zswpin 656 569 624 639 >> zswpout 9,413,603 11,284,812 9,453,761 9,385,910 >> thp_swpout 0 0 0 0 >> thp_swpout_ 0 0 0 0 >> fallback >> pgmajfault 3,470 3,382 4,633 3,611 >> ZSWPOUT-64kB n/a n/a 590,768 586,521 >> SWPOUT-64kB 0 0 0 0 >> ------------------------------------------------------------------------------- >> >> >> 2MB PMD-THP/2048K mTHP (cgroup memory.high set to 40G): >> ======================================================= >> >> ------------------------------------------------------------------------------ >> v6.11-rc3 mainline zswap-mTHP Change wrt >> Baseline Baseline >> CONFIG_THP_SWAP=N CONFIG_THP_SWAP=Y >> ------------------------------------------------------------------------------ >> ZSWAP compressor zstd deflate- zstd deflate- zstd deflate- >> iaa iaa iaa >> ------------------------------------------------------------------------------ >> Throughput (KB/s) 164,220 172,523 165,005 174,536 0.5% 1% >> sys time (sec) 855.76 686.94 801.72 676.65 6% 1% >> memcg_high 14,628 16,247 14,951 16,096 >> memcg_swap_high 0 0 0 0 >> memcg_swap_fail 18,698 21,114 0 0 >> pswpin 0 0 0 0 >> pswpout 0 0 0 0 >> zswpin 663 665 5,333 781 >> zswpout 8,419,458 8,992,065 8,546,895 9,355,760 >> thp_swpout 0 0 0 0 >> thp_swpout_ 18,697 21,113 0 0 >> fallback >> pgmajfault 3,439 3,496 8,139 3,582 >> ZSWPOUT-2048kB n/a n/a 16,684 18,270 >> SWPOUT-2048kB 0 0 0 0 >> ----------------------------------------------------------------------------- >> >> We see improvements overall in throughput and sys time for zstd and >> deflate-iaa, when comparing before (THP_SWAP=N) vs. after (THP_SWAP=Y). >> >> >> Case 2: Baseline with CONFIG_THP_SWAP enabled. >> ============================================== >> >> In this scenario, the "before" represents zswap rejecting mTHP, and the mTHP >> being stored by the backing swap device. >> >> The "after" represents data with this patch-series, that results in 64K/2M >> (m)THP being processed by zswap. >> >> 64KB mTHP (cgroup memory.high set to 40G): >> ========================================== >> >> ------------------------------------------------------------------------------ >> v6.11-rc3 mainline zswap-mTHP Change wrt >> Baseline Baseline >> ------------------------------------------------------------------------------ >> ZSWAP compressor zstd deflate- zstd deflate- zstd deflate- >> iaa iaa iaa >> ------------------------------------------------------------------------------ >> Throughput (KB/s) 161,496 156,343 140,363 151,938 -13% -3% >> sys time (sec) 771.68 802.08 954.85 735.47 -24% 8% >> memcg_high 111,223 110,889 138,651 133,884 >> memcg_swap_high 0 0 0 0 >> memcg_swap_fail 0 0 0 0 >> pswpin 16 16 0 0 >> pswpout 7,471,472 7,527,963 0 0 >> zswpin 635 605 624 639 >> zswpout 1,509 1,478 9,453,761 9,385,910 >> thp_swpout 0 0 0 0 >> thp_swpout_ 0 0 0 0 >> fallback >> pgmajfault 3,616 3,430 4,633 3,611 >> ZSWPOUT-64kB n/a n/a 590,768 586,521 >> SWPOUT-64kB 466,967 470,498 0 0 >> ------------------------------------------------------------------------------ >> >> 2MB PMD-THP/2048K mTHP (cgroup memory.high set to 40G): >> ======================================================= >> >> ------------------------------------------------------------------------------ >> v6.11-rc3 mainline zswap-mTHP Change wrt >> Baseline Baseline >> ------------------------------------------------------------------------------ >> ZSWAP compressor zstd deflate- zstd deflate- zstd deflate- >> iaa iaa iaa >> ------------------------------------------------------------------------------ >> Throughput (KB/s) 192,164 194,643 165,005 174,536 -14% -10% >> sys time (sec) 823.55 830.42 801.72 676.65 3% 19% >> memcg_high 16,054 15,936 14,951 16,096 >> memcg_swap_high 0 0 0 0 >> memcg_swap_fail 0 0 0 0 >> pswpin 0 0 0 0 >> pswpout 8,629,248 8,628,907 0 0 >> zswpin 560 645 5,333 781 >> zswpout 1,416 1,503 8,546,895 9,355,760 >> thp_swpout 16,854 16,853 0 0 >> thp_swpout_ 0 0 0 0 >> fallback >> pgmajfault 3,341 3,574 8,139 3,582 >> ZSWPOUT-2048kB n/a n/a 16,684 18,270 >> SWPOUT-2048kB 16,854 16,853 0 0 >> ------------------------------------------------------------------------------ >> >> 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. >> >> This causes degradation in throughput and sys time with zswap mTHP, more so >> in case of zstd than deflate-iaa. Compress latency could play a part in >> this - when there is more swapout activity happening, a slower compressor >> would cause allocations to stall for any/all of the 70 processes. > > We are basically comparing zram with zswap in this case, and it's not > fair because, as you mentioned, the zswap compressed data is being > accounted for while the zram compressed data isn't. I am not really > sure how valuable these test results are. Even if we remove the cgroup > accounting from zswap, we won't see an improvement, we should expect a > similar performance to zram. > > I think the test results that are really valuable are case 1, where > zswap users are currently disabling CONFIG_THP_SWAP, and get to enable > it after this series. > > If we really want to compare CONFIG_THP_SWAP on before and after, it > should be with SSD because that's a more conventional setup. In this > case the users that have CONFIG_THP_SWAP=y only experience the > benefits of zswap with this series. Yes. I think so too. > You mentioned experimenting with > usemem to keep the memory allocated longer so that you're able to have > a fair test with the small SSD swap setup. Did that work? Looking forward to the results of this test too. > I am hoping Nhat or Johannes would shed some light on whether they > usually have CONFIG_THP_SWAP enabled or not with zswap. I am trying to > figure out if any reasonable setups enable CONFIG_THP_SWAP with zswap. > Otherwise the testing results from case 1 should be sufficient. I guess that even if 2MB THP swapping may be not popular, 64KB mTHP swapping to SSD or zswap looks much more appealing. >> >> In my opinion, even though the test set up does not provide an accurate >> way for a direct before/after comparison (because of zswap usage being >> counted in cgroup, hence towards the memory.high), it still seems >> reasonable for zswap_store to support (m)THP, so that further performance >> improvements can be implemented. > > This is only referring to the results of case 2, right? > > Honestly, I wouldn't want to merge mTHP swapout support on its own > just because it enables further performance improvements without > having actual patches for them. But I don't think this captures the > results accurately as it dismisses case 1 results (which I think are > more reasonable). -- Best Regards, Huang, Ying
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