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Hugh Dickins authored
Swapping load on huge=always tmpfs (with khugepaged tuned up to be very eager, but I'm not sure that is relevant) soon hung uninterruptibly, waiting for page lock in shmem_getpage_gfp()'s find_lock_entry(), most often when "cp -a" was trying to write to a smallish file. Debug showed that the page in question was not locked, and page->mapping NULL by now, but page->index consistent with having been in a huge page before. Reproduced in minutes on a 4.15 kernel, even with 4.17's 605ca5ed ("mm/huge_memory.c: reorder operations in __split_huge_page_tail()") added in; but took hours to reproduce on a 4.17 kernel (no idea why). The culprit proved to be the __ClearPageDirty() on tails beyond i_size in __split_huge_page(): the non-atomic __bitoperation may have been safe when 4.8's baa355fd ("thp: file pages support for split_huge_page()") introduced it, but liable to erase PageWaiters after 4.10's 62906027 ("mm: add PageWaiters indicating tasks are waiting for a page bit"). Link: http://lkml.kernel.org/r/alpine.LSU.2.11.1805291841070.3197@eggly.anvils Fixes: 62906027 ("mm: add PageWaiters indicating tasks are waiting for a page bit") Signed-off-by:
Hugh Dickins <hughd@google.com> Acked-by:
Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru> Cc: Nicholas Piggin <npiggin@gmail.com> Cc: <stable@vger.kernel.org> Signed-off-by:
Andrew Morton <akpm@linux-foundation.org> Signed-off-by:
Linus Torvalds <torvalds@linux-foundation.org>
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