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authorTejun Heo <tj@kernel.org>2015-05-28 14:50:57 -0400
committerJens Axboe <axboe@fb.com>2015-06-02 08:40:20 -0600
commite8a7abf5a5bd302a1e06a3c21a629eaa4cba57d6 (patch)
tree1b585f3ccad99357f85c4cc0c2b17e5e98da4c1f /fs
parentd10c809552659d8a0089062b9d73da6d47e84cbf (diff)
writeback: disassociate inodes from dying bdi_writebacks
For the purpose of foreign inode detection, wb's (bdi_writeback's) are identified by the associated memcg ID. As we create a separate wb for each memcg, this is enough to identify the active wb's; however, when blkcg is enabled or disabled higher up in the hierarchy, the mapping between memcg and blkcg changes which in turn creates a new wb to service the new mapping. The old wb is unlinked from index and released after all references are drained. The foreign inode detection logic can't detect this condition because both the old and new wb's point to the same memcg and thus never decides to move inodes attached to the old wb to the new one. This patch adds logic to initiate switching immediately in wbc_attach_and_unlock_inode() if the associated wb is dying. We can make the usual foreign detection logic to distinguish the different wb's mapped to the memcg but the dying wb is never gonna be in active service again and there's no point in tracking the usage history and reaching the switch verdict after enough data points are collected. It's already known that the wb has to be switched. Signed-off-by: Tejun Heo <tj@kernel.org> Cc: Jens Axboe <axboe@kernel.dk> Cc: Jan Kara <jack@suse.cz> Cc: Wu Fengguang <fengguang.wu@intel.com> Cc: Greg Thelen <gthelen@google.com> Signed-off-by: Jens Axboe <axboe@fb.com>
Diffstat (limited to 'fs')
-rw-r--r--fs/fs-writeback.c7
1 files changed, 7 insertions, 0 deletions
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 5eeb24a8082f..f60de54d2042 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -525,6 +525,13 @@ void wbc_attach_and_unlock_inode(struct writeback_control *wbc,
wb_get(wbc->wb);
spin_unlock(&inode->i_lock);
+
+ /*
+ * A dying wb indicates that the memcg-blkcg mapping has changed
+ * and a new wb is already serving the memcg. Switch immediately.
+ */
+ if (unlikely(wb_dying(wbc->wb)))
+ inode_switch_wbs(inode, wbc->wb_id);
}
/**