On 2024/10/21 17:17, Barry Song wrote:
On Mon, Oct 21, 2024 at 9:14 PM Kefeng Wang <wangkefeng.wang@xxxxxxxxxx> wrote:On 2024/10/21 15:55, Barry Song wrote:On Mon, Oct 21, 2024 at 8:47 PM Barry Song <21cnbao@xxxxxxxxx> wrote:On Mon, Oct 21, 2024 at 7:09 PM Kefeng Wang <wangkefeng.wang@xxxxxxxxxx> wrote:On 2024/10/21 13:38, Barry Song wrote:On Mon, Oct 21, 2024 at 6:16 PM Kefeng Wang <wangkefeng.wang@xxxxxxxxxx> wrote: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....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 better than 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.we already have a helper like folio_zero_user()? it is not good enough?Since it is with many cond_resched(), the performance is worst...Not exactly? It should have zero cost for a preemptible kernel. For a non-preemptible kernel, it helps avoid clearing the folio from occupying the CPU and starving other processes, right?--- a/mm/shmem.c +++ b/mm/shmem.c @@ -2393,10 +2393,7 @@ static int shmem_get_folio_gfp(struct inode *inode, pgoff_t index, * it now, lest undo on failure cancel our earlier guarantee. */ if (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)); + folio_zero_user(folio, vmf->address); flush_dcache_folio(folio); folio_mark_uptodate(folio); } Do we perform better or worse with the following?Here is for SGP_FALLOC, vmf = NULL, we could use folio_zero_user(folio, 0), I think the performance is worse, will retest once I can access hardware.Perhaps, since the current code uses clear_hugepage(). Does using index << PAGE_SHIFT as the addr_hint offer any benefit?
when use folio_zero_user(), the performance is vary bad with above
fallocate test(mount huge=always),
folio_zero_range clear_highpage folio_zero_user
real 0m1.214s 0m1.111s 0m3.159s
user 0m0.000s 0m0.000s 0m0.000s
sys 0m1.210s 0m1.109s 0m3.152s
I tried with addr_hint = 0/index << PAGE_SHIFT, no obvious different.
