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authorWu Fengguang <fengguang.wu@intel.com>2011-04-27 19:05:21 -0600
committerWu Fengguang <fengguang.wu@intel.com>2011-06-08 08:25:20 +0800
commit94c3dcbb0b0cdfd82cedd21705424d8044edc42c (patch)
treef991941a1d5c5f23530e0cc4eb68bfe5d0684b9e /fs/fs-writeback.c
parent6e6938b6d3130305a5960c86b1a9b21e58cf6144 (diff)
downloadop-kernel-dev-94c3dcbb0b0cdfd82cedd21705424d8044edc42c.zip
op-kernel-dev-94c3dcbb0b0cdfd82cedd21705424d8044edc42c.tar.gz
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 'fs/fs-writeback.c')
-rw-r--r--fs/fs-writeback.c9
1 files changed, 9 insertions, 0 deletions
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 5ed2ce9..fe190a8 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -419,6 +419,15 @@ writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
spin_lock(&inode->i_lock);
inode->i_state &= ~I_SYNC;
if (!(inode->i_state & I_FREEING)) {
+ /*
+ * Sync livelock prevention. Each inode is tagged and synced in
+ * one shot. If still dirty, it will be redirty_tail()'ed below.
+ * Update the dirty time to prevent enqueue and sync it again.
+ */
+ if ((inode->i_state & I_DIRTY) &&
+ (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages))
+ inode->dirtied_when = jiffies;
+
if (mapping_tagged(mapping, PAGECACHE_TAG_DIRTY)) {
/*
* We didn't write back all the pages. nfs_writepages()
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