path: root/drivers/firewire
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authorHugh Dickins <hughd@google.com>2014-07-26 12:58:23 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2014-07-26 14:38:50 -0700
commit8bdd638091605dc66d92c57c4b80eb87fffc15f7 (patch)
treedc9d26d328a90cb250b0bb85fefb1be0e9525f28 /drivers/firewire
parentb401796c95feb9faad4065633abf90270a39fc06 (diff)
mm: fix direct reclaim writeback regression
Shortly before 3.16-rc1, Dave Jones reported: WARNING: CPU: 3 PID: 19721 at fs/xfs/xfs_aops.c:971 xfs_vm_writepage+0x5ce/0x630 [xfs]() CPU: 3 PID: 19721 Comm: trinity-c61 Not tainted 3.15.0+ #3 Call Trace: xfs_vm_writepage+0x5ce/0x630 [xfs] shrink_page_list+0x8f9/0xb90 shrink_inactive_list+0x253/0x510 shrink_lruvec+0x563/0x6c0 shrink_zone+0x3b/0x100 shrink_zones+0x1f1/0x3c0 try_to_free_pages+0x164/0x380 __alloc_pages_nodemask+0x822/0xc90 alloc_pages_vma+0xaf/0x1c0 handle_mm_fault+0xa31/0xc50 etc. 970 if (WARN_ON_ONCE((current->flags & (PF_MEMALLOC|PF_KSWAPD)) == 971 PF_MEMALLOC)) I did not respond at the time, because a glance at the PageDirty block in shrink_page_list() quickly shows that this is impossible: we don't do writeback on file pages (other than tmpfs) from direct reclaim nowadays. Dave was hallucinating, but it would have been disrespectful to say so. However, my own /var/log/messages now shows similar complaints WARNING: CPU: 1 PID: 28814 at fs/ext4/inode.c:1881 ext4_writepage+0xa7/0x38b() WARNING: CPU: 0 PID: 27347 at fs/ext4/inode.c:1764 ext4_writepage+0xa7/0x38b() from stressing some mmotm trees during July. Could a dirty xfs or ext4 file page somehow get marked PageSwapBacked, so fail shrink_page_list()'s page_is_file_cache() test, and so proceed to mapping->a_ops->writepage()? Yes, 3.16-rc1's commit 68711a746345 ("mm, migration: add destination page freeing callback") has provided such a way to compaction: if migrating a SwapBacked page fails, its newpage may be put back on the list for later use with PageSwapBacked still set, and nothing will clear it. Whether that can do anything worse than issue WARN_ON_ONCEs, and get some statistics wrong, is unclear: easier to fix than to think through the consequences. Fixing it here, before the put_new_page(), addresses the bug directly, but is probably the worst place to fix it. Page migration is doing too many parts of the job on too many levels: fixing it in move_to_new_page() to complement its SetPageSwapBacked would be preferable, except why is it (and newpage->mapping and newpage->index) done there, rather than down in migrate_page_move_mapping(), once we are sure of success? Not a cleanup to get into right now, especially not with memcg cleanups coming in 3.17. Reported-by: Dave Jones <davej@redhat.com> Signed-off-by: Hugh Dickins <hughd@google.com> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'drivers/firewire')
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