Hello, Xuejiufei. On Mon, Dec 04, 2017 at 03:13:34PM +0800, xuejiufei wrote: > I have found that system call sync may return even if dirty pages still > exist. This is caused by the following case: > > sync > -> sync_inodes_sb() > -> bdi_split_work_to_wbs() queue works for each wb > -> wb_wait_for_completions() wait for these works to complete. > > >>>>>> race window. Writeback thread found it should switch to another > new wb while doing foreign cgroup detect. So a new wb is created, and > the inodes are move from old wb to the new one. The writeback work for > old wb is done, so the sync process is woken while the inodes with dirty > pages are still queued in new wb. So, wb_wait_for_completion() may end up returning earlier than expected but data integrity is waited by wait_sb_inodes() which isn't affected by inode cgroup wb migrations. Have you actually seen this happening? Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe cgroups" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
