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authorWu Fengguang2011-04-28 03:05:21 +0200
committerWu Fengguang2011-06-08 02:25:20 +0200
commit94c3dcbb0b0cdfd82cedd21705424d8044edc42c (patch)
treef991941a1d5c5f23530e0cc4eb68bfe5d0684b9e /include/linux
parentwriteback: introduce .tagged_writepages for the WB_SYNC_NONE sync stage (diff)
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writeback: update dirtied_when for synced inode to prevent livelock
Explicitly update .dirtied_when on synced inodes, so that they are no longer considered for writeback in the next round. It can prevent both of the following livelock schemes: - while true; do echo data >> f; done - while true; do touch f; done (in theory) The exact livelock condition is, during sync(1): (1) no new inodes are dirtied (2) an inode being actively dirtied On (2), the inode will be tagged and synced with .nr_to_write=LONG_MAX. When finished, it will be redirty_tail()ed because it's still dirty and (.nr_to_write > 0). redirty_tail() won't update its ->dirtied_when on condition (1). The sync work will then revisit it on the next queue_io() and find it eligible again because its old ->dirtied_when predates the sync work start time. We'll do more aggressive "keep writeback as long as we wrote something" logic in wb_writeback(). The "use LONG_MAX .nr_to_write" trick in commit b9543dac5bbc ("writeback: avoid livelocking WB_SYNC_ALL writeback") will no longer be enough to stop sync livelock. Reviewed-by: Jan Kara <jack@suse.cz> Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
Diffstat (limited to 'include/linux')
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