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authorHugh Dickins <hughd@google.com>2013-02-22 16:36:07 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2013-02-23 17:50:23 -0800
commit5117b3b835f288314a2d4e5512bc1747e3a7c8ed (patch)
treec4267d11de7bff025bf15c3557bfa65c346bad38 /CREDITS
parentbc56620b493496b8a6962080b644ccc537f4d526 (diff)
downloadlinux-5117b3b835f288314a2d4e5512bc1747e3a7c8ed.tar.gz
mm,ksm: FOLL_MIGRATION do migration_entry_wait
In "ksm: remove old stable nodes more thoroughly" I said that I'd never seen its WARN_ON_ONCE(page_mapped(page)). True at the time of writing, but it soon appeared once I tried fuller tests on the whole series. It turned out to be due to the KSM page migration itself: unmerge_and_ remove_all_rmap_items() failed to locate and replace all the KSM pages, because of that hiatus in page migration when old pte has been replaced by migration entry, but not yet by new pte. follow_page() finds no page at that instant, but a KSM page reappears shortly after, without a fault. Add FOLL_MIGRATION flag, so follow_page() can do migration_entry_wait() for KSM's break_cow(). I'd have preferred to avoid another flag, and do it every time, in case someone else makes the same easy mistake; but did not find another transgressor (the common get_user_pages() is of course safe), and cannot be sure that every follow_page() caller is prepared to sleep - ia64's xencomm_vtop()? Now, THP's wait_split_huge_page() can already sleep there, since anon_vma locking was changed to mutex, but maybe that's somehow excluded. Signed-off-by: Hugh Dickins <hughd@google.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Petr Holasek <pholasek@redhat.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Izik Eidus <izik.eidus@ravellosystems.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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