linux-kernel - Re: Writeback bug causing writeback stalls

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Date:   Fri, 29 May 2020 17:20:36 +0200
From:   Jan Kara <jack@...e.cz>
To:     Martijn Coenen <maco@...roid.com>
Cc:     Jan Kara <jack@...e.cz>, Jaegeuk Kim <jaegeuk@...nel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Jens Axboe <axboe@...nel.dk>, miklos@...redi.hu, tj@...nel.org,
        linux-fsdevel@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
        kernel-team@...roid.com
Subject: Re: Writeback bug causing writeback stalls

Hello Martinj!

On Wed 27-05-20 10:14:09, Martijn Coenen wrote:
> On Mon, May 25, 2020 at 9:31 AM Jan Kara <jack@...e.cz> wrote:
> > Well, most importantly filesystems like ext4, xfs, btrfs don't hold i_rwsem
> > when writing back inode and that's deliberate because of performance. We
> > don't want to block writes (or event reads in case of XFS) for the inode
> > during writeback.
> 
> Thanks for clarifying, that makes sense. By the way, do you have an
> ETA for your fix? We are under some time pressure to get this fixed in
> our downstream kernels, but I'd much rather take a fix from upstream
> from somebody who knows this code well. Alternatively, I can take a
> stab at the idea you proposed and send a patch to LKML for review this
> week.

I understand. I have written a fix (attached). Currently its under testing
together with other cleanups. If everything works fine, I plan to submit
the patches on Monday.

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR

View attachment "0001-writeback-Avoid-skipping-inode-writeback.patch" of type "text/x-patch" (7849 bytes)