From: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx> Subject: mm/thp: decrease nr_thps in file's mapping on THP split Decrease nr_thps counter in file's mapping to ensure that the page cache won't be dropped excessively on file write access if page has been already split. I've tried a test scenario, where one runs a big binary, kernel remaps it with THPs, then one forces THP split with /sys/kernel/debug/split_huge_pages. During any further open of that binary with O_RDWR or O_WRITEONLY kernel drops page cache for it, because of non-zero thps counter. Link: https://lkml.kernel.org/r/20211012120237.2600-1-m.szyprowski@xxxxxxxxxxx Signed-off-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx> Fixes: 09d91cda0e82 ("mm,thp: avoid writes to file with THP in pagecache") Fixes: 06d3eff62d9d ("mm/thp: fix node page state in split_huge_page_to_list()") Acked-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx> Reviewed-by: Yang Shi <shy828301@xxxxxxxxx> Cc: <sfoon.kim@xxxxxxxxxxx> Cc: Song Liu <songliubraving@xxxxxx> Cc: Rik van Riel <riel@xxxxxxxxxxx> Cc: "Kirill A . Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx> Cc: Johannes Weiner <hannes@xxxxxxxxxxx> Cc: Hillf Danton <hdanton@xxxxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Cc: William Kucharski <william.kucharski@xxxxxxxxxx> Cc: Oleg Nesterov <oleg@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/huge_memory.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) --- a/mm/huge_memory.c~mm-thp-decrease-nr_thps-in-files-mapping-on-thp-split +++ a/mm/huge_memory.c @@ -2700,12 +2700,14 @@ int split_huge_page_to_list(struct page if (mapping) { int nr = thp_nr_pages(head); - if (PageSwapBacked(head)) + if (PageSwapBacked(head)) { __mod_lruvec_page_state(head, NR_SHMEM_THPS, -nr); - else + } else { __mod_lruvec_page_state(head, NR_FILE_THPS, -nr); + filemap_nr_thps_dec(mapping); + } } __split_huge_page(page, list, end); _
