Re: [PATCH] reiserfs: don't drop PG_dirty when releasingsub-page-sized dirty file
From: Fengguang Wu
Date: Tue Oct 23 2007 - 07:57:20 EST
On Tue, Oct 23, 2007 at 12:07:07PM +0200, Peter Zijlstra wrote:
> [ adding reiserfs devs to the CC ]
Thank you.
This fix is kind of crude - even when it fixed Maxim's problem, and
survived my stress testing of a lot of patching and kernel compiling.
I'd be glad to see better solutions.
Fengguang
---
reiserfs: don't drop PG_dirty when releasing sub-page-sized dirty file
This is not a new problem in 2.6.23-git17.
2.6.22/2.6.23 is buggy in the same way.
Reiserfs could accumulate dirty sub-page-size files until umount time.
They cannot be synced to disk by pdflush routines or explicit `sync'
commands. Only `umount' can do the trick.
The direct cause is: the dirty page's PG_dirty is wrongly _cleared_.
Call trace:
[<ffffffff8027e920>] cancel_dirty_page+0xd0/0xf0
[<ffffffff8816d470>] :reiserfs:reiserfs_cut_from_item+0x660/0x710
[<ffffffff8816d791>] :reiserfs:reiserfs_do_truncate+0x271/0x530
[<ffffffff8815872d>] :reiserfs:reiserfs_truncate_file+0xfd/0x3b0
[<ffffffff8815d3d0>] :reiserfs:reiserfs_file_release+0x1e0/0x340
[<ffffffff802a187c>] __fput+0xcc/0x1b0
[<ffffffff802a1ba6>] fput+0x16/0x20
[<ffffffff8029e676>] filp_close+0x56/0x90
[<ffffffff8029fe0d>] sys_close+0xad/0x110
[<ffffffff8020c41e>] system_call+0x7e/0x83
Fix the bug by removing the cancel_dirty_page() call. Tests show that
it causes no bad behaviors on various write sizes.
=== for the patient ===
Here are more detailed demonstrations of the problem.
1) the page has both PG_dirty(D)/PAGECACHE_TAG_DIRTY(d) after being written to;
and then only PAGECACHE_TAG_DIRTY(d) remains after the file is closed.
------------------------------ screen 0 ------------------------------
[T0] root /home/wfg# cat > /test/tiny
[T1] hi
[T2] root /home/wfg#
------------------------------ screen 1 ------------------------------
[T1] root /home/wfg# echo /test/tiny > /proc/filecache
[T1] root /home/wfg# cat /proc/filecache
# file /test/tiny
# flags R:referenced A:active M:mmap U:uptodate D:dirty W:writeback O:owner B:buffer d:dirty w:writeback
# idx len state refcnt
0 1 ___UD__Bd_ 2
[T2] root /home/wfg# cat /proc/filecache
# file /test/tiny
# flags R:referenced A:active M:mmap U:uptodate D:dirty W:writeback O:owner B:buffer d:dirty w:writeback
# idx len state refcnt
0 1 ___U___Bd_ 2
2) note the non-zero 'cancelled_write_bytes' after /tmp/hi is copied.
------------------------------ screen 0 ------------------------------
[T0] root /home/wfg# echo hi > /tmp/hi
[T1] root /home/wfg# cp /tmp/hi /dev/stdin /test
[T2] hi
[T3] root /home/wfg#
------------------------------ screen 1 ------------------------------
[T1] root /proc/4397# cd /proc/`pidof cp`
[T1] root /proc/4713# cat io
rchar: 8396
wchar: 3
syscr: 20
syscw: 1
read_bytes: 0
write_bytes: 20480
cancelled_write_bytes: 4096
[T2] root /proc/4713# cat io
rchar: 8399
wchar: 6
syscr: 21
syscw: 2
read_bytes: 0
write_bytes: 24576
cancelled_write_bytes: 4096
//Question: the 'write_bytes' is a bit more than expected ;-)
Cc: Maxim Levitsky <maximlevitsky@xxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Jeff Mahoney <jeffm@xxxxxxxx>
Signed-off-by: Fengguang Wu <wfg@xxxxxxxxxxxxxxxx>
---
fs/reiserfs/stree.c | 3 ---
1 file changed, 3 deletions(-)
--- linux-2.6.24-git17.orig/fs/reiserfs/stree.c
+++ linux-2.6.24-git17/fs/reiserfs/stree.c
@@ -1458,9 +1458,6 @@ static void unmap_buffers(struct page *p
}
bh = next;
} while (bh != head);
- if (PAGE_SIZE == bh->b_size) {
- cancel_dirty_page(page, PAGE_CACHE_SIZE);
- }
}
}
}
-
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