On 2024/10/21 12:15, Barry Song wrote:
On Fri, Oct 18, 2024 at 8:48 PM Kefeng Wang <wangkefeng.wang@xxxxxxxxxx> wrote:On 2024/10/18 15:32, Kefeng Wang wrote:On 2024/10/18 13:23, Barry Song wrote:On Fri, Oct 18, 2024 at 6:20 PM Kefeng Wang <wangkefeng.wang@xxxxxxxxxx> wrote:On 2024/10/17 23:09, Matthew Wilcox wrote:On Thu, Oct 17, 2024 at 10:25:04PM +0800, Kefeng Wang wrote:Directly use folio_zero_range() to cleanup code.Are you sure there's no performance regression introduced by this? clear_highpage() is often optimised in ways that we can't optimise for a plain memset(). On the other hand, if the folio is large, maybe a modern CPU will be able to do better than clear-one-page-at-a-time.Right, I missing this, clear_page might be better than memset, I change this one when look at the shmem_writepage(), which already convert to use folio_zero_range() from clear_highpage(), also I grep folio_zero_range(), there are some other to use folio_zero_range(). fs/bcachefs/fs-io-buffered.c: folio_zero_range(folio, 0, folio_size(folio)); fs/bcachefs/fs-io-buffered.c: folio_zero_range(f, 0, folio_size(f)); fs/bcachefs/fs-io-buffered.c: folio_zero_range(f, 0, folio_size(f)); fs/libfs.c: folio_zero_range(folio, 0, folio_size(folio)); fs/ntfs3/frecord.c: folio_zero_range(folio, 0, folio_size(folio)); mm/page_io.c: folio_zero_range(folio, 0, folio_size(folio)); mm/shmem.c: folio_zero_range(folio, 0, folio_size(folio));IOW, what performance testing have you done with this patch?No performance test before, but I write a testcase, 1) allocate N large folios (folio_alloc(PMD_ORDER)) 2) then calculate the diff(us) when clear all N folios clear_highpage/folio_zero_range/folio_zero_user 3) release N folios the result(run 5 times) shown below on my machine, N=1, clear_highpage folio_zero_range folio_zero_user 1 69 74 177 2 57 62 168 3 54 58 234 4 54 58 157 5 56 62 148 avg 58 62.8 176.8 N=100 clear_highpage folio_zero_range folio_zero_user 1 11015 11309 32833 2 10385 11110 49751 3 10369 11056 33095 4 10332 11017 33106 5 10483 11000 49032 avg 10516.8 11098.4 39563.4 N=512 clear_highpage folio_zero_range folio_zero_user 1 55560 60055 156876 2 55485 60024 157132 3 55474 60129 156658 4 55555 59867 157259 5 55528 59932 157108 avg 55520.4 60001.4 157006.6 folio_zero_user with many cond_resched(), so time fluctuates a lot, clear_highpage is better folio_zero_range as you said. Maybe add a new helper to convert all folio_zero_range(folio, 0, folio_size(folio)) to use clear_highpage + flush_dcache_folio?If this also improves performance for other existing callers of folio_zero_range(), then that's a positive outcome.rm -f /tmp/test && fallocate -l 20G /tmp/test && fallocate -d -l 20G / tmp/test && time fallocate -l 20G /tmp/test 1）mount always(2M folio) with patch without patch real 0m1.214s 0m1.111s user 0m0.000s 0m0.000s sys 0m1.210s 0m1.109s With this patch, the performance does have regression, folio_zero_range() is bad than clear_highpage + flush_dcache_folio with patchOh, this should without patch since it uses clear_highpage,99.95% 0.00% fallocate [kernel.vmlinux] [k] vfs_fallocate vfs_fallocate - shmem_fallocate 98.54% __pi_clear_page - 1.38% shmem_get_folio_gfp filemap_get_entryand this one is with patchwithout patch 99.89% 0.00% fallocate [kernel.vmlinux] [k] shmem_fallocate shmem_fallocate - shmem_get_folio_gfp 90.12% __memset - 9.42% zero_user_segments.constprop.0 8.16% flush_dcache_page 1.03% flush_dcache_folio 2）mount never (4K folio) real 0m3.159s 0m3.176s user 0m0.000s 0m0.000s sys 0m3.150s 0m3.169s But with this patch, the performance is improved a little, folio_zero_range() is better than clear_highpage + flush_dcache_folioFor 4K, the result is fluctuating, so maybe no different.hi Kefeng, what's your point? providing a helper like clear_highfolio() or similar?
Yes, from above test, using clear_highpage/flush_dcache_folio is betterthan using folio_zero_range() for folio zero(especially for large folio), so I'd like to add a new helper, maybe name it folio_zero()
since it zero the whole folio.
with patch 97.77% 3.37% fallocate [kernel.vmlinux] [k] shmem_fallocate - 94.40% shmem_fallocate - 93.70% shmem_get_folio_gfp 66.60% __memset - 7.43% filemap_get_entry 3.49% xas_load 1.32% zero_user_segments.constprop.0 without patch 97.82% 3.22% fallocate [kernel.vmlinux] [k] shmem_fallocate - 94.61% shmem_fallocate 68.18% __pi_clear_page - 25.60% shmem_get_folio_gfp - 7.64% filemap_get_entry 3.51% xas_loadif (sgp != SGP_WRITE && !folio_test_uptodate(folio)) { - long i, n = folio_nr_pages(folio); - - for (i = 0; i < n; i++) - clear_highpage(folio_page(folio, i)); - flush_dcache_folio(folio); + folio_zero_range(folio, 0, folio_size(folio)); folio_mark_uptodate(folio); }Thanks Barry
