On 22/10/2024 21:46, Barry Song wrote: > On Wed, Oct 23, 2024 at 4:26 AM Usama Arif <usamaarif642@xxxxxxxxx> wrote: >> >> >> >> On 21/10/2024 11:40, Usama Arif wrote: >>> >>> >>> On 21/10/2024 06:09, Barry Song wrote: >>>> On Fri, Oct 18, 2024 at 11:50 PM Usama Arif <usamaarif642@xxxxxxxxx> wrote: >>>>> >>>>> After large folio zswapout support added in [1], this patch adds >>>>> support for zswapin of large folios to bring it on par with zram. >>>>> This series makes sure that the benefits of large folios (fewer >>>>> page faults, batched PTE and rmap manipulation, reduced lru list, >>>>> TLB coalescing (for arm64 and amd)) are not lost at swap out when >>>>> using zswap. >>>>> >>>>> It builds on top of [2] which added large folio swapin support for >>>>> zram and provides the same level of large folio swapin support as >>>>> zram, i.e. only supporting swap count == 1. >>>>> >>>>> Patch 1 skips swapcache for swapping in zswap pages, this should improve >>>>> no readahead swapin performance [3], and also allows us to build on large >>>>> folio swapin support added in [2], hence is a prerequisite for patch 3. >>>>> >>>>> Patch 3 adds support for large folio zswapin. This patch does not add >>>>> support for hybrid backends (i.e. folios partly present swap and zswap). >>>>> >>>>> The main performance benefit comes from maintaining large folios *after* >>>>> swapin, large folio performance improvements have been mentioned in previous >>>>> series posted on it [2],[4], so have not added those. Below is a simple >>>>> microbenchmark to measure the time needed *for* zswpin of 1G memory (along >>>>> with memory integrity check). >>>>> >>>>> | no mTHP (ms) | 1M mTHP enabled (ms) >>>>> Base kernel | 1165 | 1163 >>>>> Kernel with mTHP zswpin series | 1203 | 738 >>>> >>>> Hi Usama, >>>> Do you know where this minor regression for non-mTHP comes from? >>>> As you even have skipped swapcache for small folios in zswap in patch1, >>>> that part should have some gain? is it because of zswap_present_test()? >>>> >>> >>> Hi Barry, >>> >>> The microbenchmark does a sequential read of 1G of memory, so it probably >>> isnt very representative of real world usecases. This also means that >>> swap_vma_readahead is able to readahead accurately all pages in its window. >>> With this patch series, if doing 4K swapin, you get 1G/4K calls of fast >>> do_swap_page. Without this patch, you get 1G/(4K*readahead window) of slow >>> do_swap_page calls. I had added some prints and I was seeing 8 pages being >>> readahead in 1 do_swap_page. The larger number of calls causes the slight >>> regression (eventhough they are quite fast). I think in a realistic scenario, >>> where readahead window wont be as large, there wont be a regression. >>> The cost of zswap_present_test in the whole call stack of swapping page is >>> very low and I think can be ignored. >>> >>> I think the more interesting thing is what Kanchana pointed out in >>> https://lore.kernel.org/all/f2f2053f-ec5f-46a4-800d-50a3d2e61bff@xxxxxxxxx/ >>> I am curious, did you see this when testing large folio swapin and compression >>> at 4K granuality? Its looks like swap thrashing so I think it would be common >>> between zswap and zram. I dont have larger granuality zswap compression done, >>> which is why I think there is a regression in time taken. (It could be because >>> its tested on intel as well). >>> >>> Thanks, >>> Usama >>> >> >> Hi, >> >> So I have been doing some benchmarking after Kanchana pointed out a performance >> regression in [1] of swapping in large folio. I would love to get thoughts from >> zram folks on this, as thats where large folio swapin was first added [2]. >> As far as I can see, the current support in zram is doing large folio swapin >> at 4K granuality. The large granuality compression in [3] which was posted >> in March is not merged, so I am currently comparing upstream zram with this series. >> >> With the microbenchmark below of timing 1G swapin, there was a very large improvement >> in performance by using this series. I think similar numbers would be seen in zram. > > Imagine running several apps on a phone and switching > between them: A → B → C → D → E … → A → B … The app > currently on the screen retains its memory, while the ones > sent to the background are swapped out. When we bring > those apps back to the foreground, their memory is restored. > This behavior is quite similar to what you're seeing with > your microbenchmark. > Hi Barry, Thanks for explaining this! Do you know if there is some open source benchmark we could use to show an improvement in app switching with large folios? Also I guess swap thrashing can happen when apps are brought back to foreground? >> >> But when doing kernel build test, Kanchana saw a regression in [1]. I believe >> its because of swap thrashing (causing large zswap activity), due to larger page swapin. >> The part of the code that decides large folio swapin is the same between zswap and zram, >> so I believe this would be observed in zram as well. > > Is this an extreme case where the workload's working set far > exceeds the available memory by memcg limitation? I doubt mTHP > would provide any real benefit from the start if the workload is bound to > experience swap thrashing. What if we disable mTHP entirely? > I would agree, this is an extreme case. I wanted (z)swap activity to happen so limited memory.max to 4G. mTHP is beneficial in kernel test benchmarking going from no mTHP to 16K: ARM make defconfig; time make -j$(nproc) Image, cgroup memory.max=4G metric no mTHP 16K mTHP=always real 1m0.613s 0m52.008s user 25m23.028s 25m19.488s sys 25m45.466s 18m11.640s zswpin 1911194 3108438 zswpout 6880815 9374628 pgfault 120430166 48976658 pgmajfault 1580674 2327086 >> >> My initial thought was this might be because its intel, where you dont have the advantage >> of TLB coalescing, so tested on AMD and ARM, but the regression is there on AMD >> and ARM as well, though a bit less (have added the numbers below). >> >> The numbers show that the zswap activity increases and page faults decrease. >> Overall this does result in sys time increasing and real time slightly increases, >> likely because the cost of increased zswap activity is more than the benefit of >> lower page faults. >> I can see in [3] that pagefaults reduced in zram as well. >> >> Large folio swapin shows good numbers in microbenchmarks that just target reduce page >> faults and sequential swapin only, but not in kernel build test. Is a similar regression >> observed with zram when enabling large folio swapin on kernel build test? Maybe large >> folio swapin makes more sense on workloads where mappings are kept for a longer time? >> > > I suspect this is because mTHP doesn't always benefit workloads > when available memory is quite limited compared to the working set. > In that case, mTHP swap-in might introduce more features that > exacerbate the problem. We used to have an extra control "swapin_enabled" > for swap-in, but it never gained much traction: > https://lore.kernel.org/linux-mm/20240726094618.401593-5-21cnbao@xxxxxxxxx/ > We can reconsider whether to include the knob, but if it's better > to disable mTHP entirely for these cases, we can still adhere to > the policy of "enabled". > Yes I think this makes sense to have. The only thing is, its too many knobs! I personally think its already difficult to decide upto which mTHP size we should enable (and I think this changes per workload). But if we add swapin_enabled on top of that it can make things more difficult. > Using large block compression and decompression in zRAM will > significantly reduce CPU usage, likely making the issue unnoticeable. > However, the default minimum size for large block support is currently > set to 64KB(ZSMALLOC_MULTI_PAGES_ORDER = 4). > I saw that the patch was sent in March, and there werent any updates after? Maybe I can try and cherry-pick that and see if we can develop large granularity compression for zswap. >> >> Kernel build numbers in cgroup with memory.max=4G to trigger zswap >> Command for AMD: make defconfig; time make -j$(nproc) bzImage >> Command for ARM: make defconfig; time make -j$(nproc) Image >> >> >> AMD 16K+32K THP=always >> metric mm-unstable mm-unstable + large folio zswapin series >> real 1m23.038s 1m23.050s >> user 53m57.210s 53m53.437s >> sys 7m24.592s 7m48.843s >> zswpin 612070 999244 >> zswpout 2226403 2347979 >> pgfault 20667366 20481728 >> pgmajfault 385887 269117 >> >> AMD 16K+32K+64K THP=always >> metric mm-unstable mm-unstable + large folio zswapin series >> real 1m22.975s 1m23.266s >> user 53m51.302s 53m51.069s >> sys 7m40.168s 7m57.104s >> zswpin 676492 1258573 >> zswpout 2449839 2714767 >> pgfault 17540746 17296555 >> pgmajfault 429629 307495 >> -------------------------- >> ARM 16K+32K THP=always >> metric mm-unstable mm-unstable + large folio zswapin series >> real 0m51.168s 0m52.086s >> user 25m14.715s 25m15.765s >> sys 17m18.856s 18m8.031s >> zswpin 3904129 7339245 >> zswpout 11171295 13473461 >> pgfault 37313345 36011338 >> pgmajfault 2726253 1932642 >> >> >> ARM 16K+32K+64K THP=always >> metric mm-unstable mm-unstable + large folio zswapin series >> real 0m52.017s 0m53.828s >> user 25m2.742s 25m0.046s >> sys 18m24.525s 20m26.207s >> zswpin 4853571 8908664 >> zswpout 12297199 15768764 >> pgfault 32158152 30425519 >> pgmajfault 3320717 2237015 >> >> >> Thanks! >> Usama >> >> >> [1] https://lore.kernel.org/all/f2f2053f-ec5f-46a4-800d-50a3d2e61bff@xxxxxxxxx/ >> [2] https://lore.kernel.org/all/20240821074541.516249-3-hanchuanhua@xxxxxxxx/ >> [3] https://lore.kernel.org/all/20240327214816.31191-1-21cnbao@xxxxxxxxx/ >> >>> >>>>> >>>>> The time measured was pretty consistent between runs (~1-2% variation). >>>>> There is 36% improvement in zswapin time with 1M folios. The percentage >>>>> improvement is likely to be more if the memcmp is removed. >>>>> >>>>> diff --git a/tools/testing/selftests/cgroup/test_zswap.c b/tools/testing/selftests/cgroup/test_zswap.c >>>>> index 40de679248b8..77068c577c86 100644 >>>>> --- a/tools/testing/selftests/cgroup/test_zswap.c >>>>> +++ b/tools/testing/selftests/cgroup/test_zswap.c >>>>> @@ -9,6 +9,8 @@ >>>>> #include <string.h> >>>>> #include <sys/wait.h> >>>>> #include <sys/mman.h> >>>>> +#include <sys/time.h> >>>>> +#include <malloc.h> >>>>> >>>>> #include "../kselftest.h" >>>>> #include "cgroup_util.h" >>>>> @@ -407,6 +409,74 @@ static int test_zswap_writeback_disabled(const char *root) >>>>> return test_zswap_writeback(root, false); >>>>> } >>>>> >>>>> +static int zswapin_perf(const char *cgroup, void *arg) >>>>> +{ >>>>> + long pagesize = sysconf(_SC_PAGESIZE); >>>>> + size_t memsize = MB(1*1024); >>>>> + char buf[pagesize]; >>>>> + int ret = -1; >>>>> + char *mem; >>>>> + struct timeval start, end; >>>>> + >>>>> + mem = (char *)memalign(2*1024*1024, memsize); >>>>> + if (!mem) >>>>> + return ret; >>>>> + >>>>> + /* >>>>> + * Fill half of each page with increasing data, and keep other >>>>> + * half empty, this will result in data that is still compressible >>>>> + * and ends up in zswap, with material zswap usage. >>>>> + */ >>>>> + for (int i = 0; i < pagesize; i++) >>>>> + buf[i] = i < pagesize/2 ? (char) i : 0; >>>>> + >>>>> + for (int i = 0; i < memsize; i += pagesize) >>>>> + memcpy(&mem[i], buf, pagesize); >>>>> + >>>>> + /* Try and reclaim allocated memory */ >>>>> + if (cg_write_numeric(cgroup, "memory.reclaim", memsize)) { >>>>> + ksft_print_msg("Failed to reclaim all of the requested memory\n"); >>>>> + goto out; >>>>> + } >>>>> + >>>>> + gettimeofday(&start, NULL); >>>>> + /* zswpin */ >>>>> + for (int i = 0; i < memsize; i += pagesize) { >>>>> + if (memcmp(&mem[i], buf, pagesize)) { >>>>> + ksft_print_msg("invalid memory\n"); >>>>> + goto out; >>>>> + } >>>>> + } >>>>> + gettimeofday(&end, NULL); >>>>> + printf ("zswapin took %fms to run.\n", (end.tv_sec - start.tv_sec)*1000 + (double)(end.tv_usec - start.tv_usec) / 1000); >>>>> + ret = 0; >>>>> +out: >>>>> + free(mem); >>>>> + return ret; >>>>> +} >>>>> + >>>>> +static int test_zswapin_perf(const char *root) >>>>> +{ >>>>> + int ret = KSFT_FAIL; >>>>> + char *test_group; >>>>> + >>>>> + test_group = cg_name(root, "zswapin_perf_test"); >>>>> + if (!test_group) >>>>> + goto out; >>>>> + if (cg_create(test_group)) >>>>> + goto out; >>>>> + >>>>> + if (cg_run(test_group, zswapin_perf, NULL)) >>>>> + goto out; >>>>> + >>>>> + ret = KSFT_PASS; >>>>> +out: >>>>> + cg_destroy(test_group); >>>>> + free(test_group); >>>>> + return ret; >>>>> +} >>>>> + >>>>> /* >>>>> * When trying to store a memcg page in zswap, if the memcg hits its memory >>>>> * limit in zswap, writeback should affect only the zswapped pages of that >>>>> @@ -584,6 +654,7 @@ struct zswap_test { >>>>> T(test_zswapin), >>>>> T(test_zswap_writeback_enabled), >>>>> T(test_zswap_writeback_disabled), >>>>> + T(test_zswapin_perf), >>>>> T(test_no_kmem_bypass), >>>>> T(test_no_invasive_cgroup_shrink), >>>>> }; >>>>> >>>>> [1] https://lore.kernel.org/all/20241001053222.6944-1-kanchana.p.sridhar@xxxxxxxxx/ >>>>> [2] https://lore.kernel.org/all/20240821074541.516249-1-hanchuanhua@xxxxxxxx/ >>>>> [3] https://lore.kernel.org/all/1505886205-9671-5-git-send-email-minchan@xxxxxxxxxx/T/#u >>>>> [4] https://lwn.net/Articles/955575/ >>>>> >>>>> Usama Arif (4): >>>>> mm/zswap: skip swapcache for swapping in zswap pages >>>>> mm/zswap: modify zswap_decompress to accept page instead of folio >>>>> mm/zswap: add support for large folio zswapin >>>>> mm/zswap: count successful large folio zswap loads >>>>> >>>>> Documentation/admin-guide/mm/transhuge.rst | 3 + >>>>> include/linux/huge_mm.h | 1 + >>>>> include/linux/zswap.h | 6 ++ >>>>> mm/huge_memory.c | 3 + >>>>> mm/memory.c | 16 +-- >>>>> mm/page_io.c | 2 +- >>>>> mm/zswap.c | 120 ++++++++++++++------- >>>>> 7 files changed, 99 insertions(+), 52 deletions(-) >>>>> >>>>> -- >>>>> 2.43.5 >>>>> >>>> > > Thanks > Barry
