From: Baolin Wang Date: Thu, 18 Sep 2025 03:46:53 +0000 (+0800) Subject: mm: vmscan: remove folio_test_private() check in pageout() X-Git-Tag: v6.19-rc1~112^2~151 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=d94d9293a1ecde99514026950ded294dd5562e30;p=thirdparty%2Fkernel%2Flinux.git mm: vmscan: remove folio_test_private() check in pageout() Patch series "some cleanups for pageout()", v2. Since we no longer attempt to write back filesystem folios in pageout(), and only tmpfs/shmem folios and anonymous swapcache folios can be written back, we can remove the redundant folio_test_private() related logic to simplify the logic of pageout(), as tmpfs/shmem and swapcache folios do not use the PG_private flag. This patch (of 2): The folio_test_private() check in pageout() was introduced by commit ce91b575332b ("orphaned pagecache memleak fix") in 2005 (checked from a history tree[1]). As the commit message mentioned, it was to address the issue where reiserfs pagecache may be truncated while still pinned. To further explain, the truncation removes the page->mapping, but the page is still listed in the VM queues because it still has buffers. In 2008, commit a2b345642f530 ("Fix dirty page accounting leak with ext3 data=journal") seems to be dealing with a similar issue, where the page becomes dirty after truncation, and it provides a very useful call stack: truncate_complete_page() cancel_dirty_page() // PG_dirty cleared, decr. dirty pages do_invalidatepage() ext3_invalidatepage() journal_invalidatepage() journal_unmap_buffer() __dispose_buffer() __journal_unfile_buffer() __journal_temp_unlink_buffer() mark_buffer_dirty(); // PG_dirty set, incr. dirty pages In this commit a2b345642f530, we forcefully clear the page's dirty flag during truncation (in truncate_complete_page()). Now it seems this was just a peculiar usage specific to reiserfs. Maybe reiserfs had some extra refcount on these pages, which caused them to pass the is_page_cache_freeable() check. With the fix provided by commit a2b345642f530 and reiserfs being removed in 2024 by commit fb6f20ecb121 ("reiserfs: The last commit"), such a case is unlikely to occur again. So let's remove the redundant folio_test_private() checks and related buffer_head release logic, and just leave a warning here to catch such a bug. [akpm@linux-foundation.org: redo comment, per David] Link: https://lkml.kernel.org/r/17d1b293-e393-4989-a357-7eea74b3c805@redhat.com [baolin.wang@linux.alibaba.com: remove comment and WARNing, per Hugh and others] Link: https://lkml.kernel.org/r/392a9ca3-31ac-4447-bd44-3c656d63e4ca@linux.alibaba.com Link: https://lkml.kernel.org/r/cover.1758166683.git.baolin.wang@linux.alibaba.com Link: https://lkml.kernel.org/r/9ef0e560dc83650bc538eb5dcd1594e112c1369f.1758166683.git.baolin.wang@linux.alibaba.com Link: https://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git [1] Signed-off-by: Baolin Wang Acked-by: David Hildenbrand Acked-by: Shakeel Butt Cc: Hugh Dickins Cc: Johannes Weiner Cc: Lorenzo Stoakes Cc: Matthew Wilcox (Oracle) Cc: Michal Hocko Cc: Qi Zheng Signed-off-by: Andrew Morton --- diff --git a/mm/vmscan.c b/mm/vmscan.c index c23c9616052ab..0684da19aa64e 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -697,23 +697,8 @@ static pageout_t pageout(struct folio *folio, struct address_space *mapping, * swap_backing_dev_info is bust: it doesn't reflect the * congestion state of the swapdevs. Easy to fix, if needed. */ - if (!is_page_cache_freeable(folio)) + if (!is_page_cache_freeable(folio) || !mapping) return PAGE_KEEP; - if (!mapping) { - /* - * Some data journaling orphaned folios can have - * folio->mapping == NULL while being dirty with clean buffers. - */ - if (folio_test_private(folio)) { - if (try_to_free_buffers(folio)) { - folio_clear_dirty(folio); - pr_info("%s: orphaned folio\n", __func__); - return PAGE_CLEAN; - } - } - return PAGE_KEEP; - } - if (!shmem_mapping(mapping) && !folio_test_anon(folio)) return PAGE_ACTIVATE; if (!folio_clear_dirty_for_io(folio))