On Wed, Jun 08, 2011 at 07:03:13AM +0800, Andrew Morton wrote:
> On Wed, 08 Jun 2011 05:32:39 +0800
> Wu Fengguang <fengguang.wu@xxxxxxxxx> wrote:
>
> > The flusher works on dirty inodes in batches, and may quit prematurely
> > if the batch of inodes happen to be metadata-only dirtied: in this case
> > wbc->nr_to_write won't be decreased at all, which stands for "no pages
> > written" but also mis-interpreted as "no progress".
> >
> > So introduce writeback_control.inodes_cleaned to count the inodes get
> > cleaned. A non-zero value means there are some progress on writeback,
> > in which case more writeback can be tried.
>
> Yes, that makes sense. I had a workload which demonstrated/exploited
> this nine years ago but I never got around to fixing it, never told
> anyone and nobody noticed ;)
Good to know that :)
> > + long inodes_cleaned; /* # of inodes cleaned */
>
> nanonit: I'd call this inodes_written, because they may not actually be
> clean.
Yeah, at least for ext4.
Done the rename. Also added a note that it's not the exact number of
inodes written.
Thanks,
Fengguang
---
Subject: writeback: introduce writeback_control.inodes_written
Date: Wed Jul 21 22:50:57 CST 2010
The flusher works on dirty inodes in batches, and may quit prematurely
if the batch of inodes happen to be metadata-only dirtied: in this case
wbc->nr_to_write won't be decreased at all, which stands for "no pages
written" but also mis-interpreted as "no progress".
So introduce writeback_control.inodes_written to count the inodes get
cleaned from VFS POV. A non-zero value means there are some progress on
writeback, in which case more writeback can be tried.
Acked-by: Jan Kara <jack@xxxxxxx>
Acked-by: Mel Gorman <mel@xxxxxxxxx>
Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
---
fs/fs-writeback.c | 4 ++++
include/linux/writeback.h | 1 +
2 files changed, 5 insertions(+)
about v1: The initial version was to count successful ->write_inode()
calls. However it leads to busy loops for sync() over NFS, because NFS
ridiculously returns 0 (success) while at the same time redirties the
inode. The NFS case can be trivially fixed, however there may be more
hidden bugs in other filesystems..
--- linux-next.orig/fs/fs-writeback.c 2011-05-24 11:17:16.000000000 +0800
+++ linux-next/fs/fs-writeback.c 2011-05-24 11:17:16.000000000 +0800
@@ -464,6 +464,7 @@ writeback_single_inode(struct inode *ino
* No need to add it back to the LRU.
*/
list_del_init(&inode->i_wb_list);
+ wbc->inodes_written++;
}
}
inode_sync_complete(inode);
@@ -725,6 +726,7 @@ static long wb_writeback(struct bdi_writ
wbc.more_io = 0;
wbc.nr_to_write = write_chunk;
wbc.pages_skipped = 0;
+ wbc.inodes_written = 0;
trace_wbc_writeback_start(&wbc, wb->bdi);
if (work->sb)
@@ -741,6 +743,8 @@ static long wb_writeback(struct bdi_writ
*/
if (wbc.nr_to_write <= 0)
continue;
+ if (wbc.inodes_written)
+ continue;
/*
* Didn't write everything and we don't have more IO, bail
*/
--- linux-next.orig/include/linux/writeback.h 2011-05-24 11:17:14.000000000 +0800
+++ linux-next/include/linux/writeback.h 2011-05-24 11:17:16.000000000 +0800
@@ -34,6 +34,7 @@ struct writeback_control {
long nr_to_write; /* Write this many pages, and decrement
this for each page written */
long pages_skipped; /* Pages which were not written */
+ long inodes_written; /* # of inodes written (at least) */
/*
* For a_ops->writepages(): is start or end are non-zero then this is
--
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