On Thu, Mar 31, 2011 at 10:34:03AM -0400, Chris Mason wrote: [..] > > > > For me knowing this is also important in another context of absolute IO > > throttling. > > > > - If a fsync is in progress and gets throttled at device, what impact it > > has on other file system operations. What gets serialized behind it. > > It depends. atime updates log inodes and logging needs a transaction > and transactions sometimes need to wait for the last transaction to > finish. So its very possible you'll make anything using the FS appear > to stop. I think I have run into this. I created a cgroup and gave ridiculously low limit of 1bytes/sec and did a fsync. This process blocks. Later I did "ls" in the directory where fsync process is blocked and ls also hangs. Following is backtrace. Looks like atime update led to some kind of blocking in do_get_write_access(). ls D ffffffff8160b060 0 5936 5192 0x00000000 ffff880138729c48 0000000000000086 0000000000000000 0000000100000010 0000000000000000 ffff88013fc40100 ffff88013ac7ac00 000000012e5d70f3 ffff8801353d7af8 ffff880138729fd8 000000000000f558 ffff8801353d7af8 Call Trace: [<ffffffffa035b0dd>] do_get_write_access+0x29d/0x500 [jbd2] [<ffffffff8108e150>] ? wake_bit_function+0x0/0x50 [<ffffffffa035b491>] jbd2_journal_get_write_access+0x31/0x50 [jbd2] [<ffffffffa03a7328>] __ext4_journal_get_write_access+0x38/0x80 [ext4] [<ffffffffa0383843>] ext4_reserve_inode_write+0x73/0xa0 [ext4] [<ffffffffa037c618>] ? call_filldir+0x78/0xe0 [ext4] [<ffffffffa03838bc>] ext4_mark_inode_dirty+0x4c/0x1d0 [ext4] [<ffffffff81041594>] ? __do_page_fault+0x1e4/0x480 [<ffffffffa0383bb0>] ext4_dirty_inode+0x40/0x60 [ext4] [<ffffffff8119a21b>] __mark_inode_dirty+0x3b/0x160 [<ffffffff8118acad>] touch_atime+0x12d/0x170 [<ffffffff81184c00>] ? filldir+0x0/0xe0 [<ffffffff81184e96>] vfs_readdir+0xd6/0xe0 [<ffffffff81185009>] sys_getdents+0x89/0xf0 [<ffffffff814dc635>] ? page_fault+0x25/0x30 [<ffffffff8100b172>] system_call_fastpath+0x16/0x1b The vim process doing fsync trace is as follows. This is waiting for some IO to finish which has been throttled at the device. vim D ffffffff8110d1f0 0 5934 4452 0x00000000 ffff880107e2dcc8 0000000000000086 0000000100000000 0000000000000003 ffff8801351f4538 0000000000000000 ffff880107e2dc68 ffffffff810e7da2 ffff8801353d70b8 ffff880107e2dfd8 000000000000f558 ffff8801353d70b8 Call Trace: [<ffffffff810e7da2>] ? ring_buffer_lock_reserve+0xa2/0x160 [<ffffffff81098cb9>] ? ktime_get_ts+0xa9/0xe0 [<ffffffff8110d1f0>] ? sync_page+0x0/0x50 [<ffffffff814da123>] io_schedule+0x73/0xc0 [<ffffffff8110d22d>] sync_page+0x3d/0x50 [<ffffffff814da98f>] __wait_on_bit+0x5f/0x90 [<ffffffff8110d3e3>] wait_on_page_bit+0x73/0x80 [<ffffffff8108e150>] ? wake_bit_function+0x0/0x50 [<ffffffff81123195>] ? pagevec_lookup_tag+0x25/0x40 [<ffffffff8110d7fb>] wait_on_page_writeback_range+0xfb/0x190 [<ffffffff81122341>] ? do_writepages+0x21/0x40 [<ffffffff8110d94b>] ? __filemap_fdatawrite_range+0x5b/0x60 [<ffffffff8110d9c8>] filemap_write_and_wait_range+0x78/0x90 [<ffffffff8119f5fe>] vfs_fsync_range+0x7e/0xe0 [<ffffffff8119f6cd>] vfs_fsync+0x1d/0x20 [<ffffffff8119f70e>] do_fsync+0x3e/0x60 [<ffffffff8119f760>] sys_fsync+0x10/0x20 [<ffffffff8100b172>] system_call_fastpath+0x16/0x1b Thanks Vivek -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
