From: Dave Chinner <david@fromorbit.com>
To: Jan Kara <jack@suse.cz>
Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
npiggin@kernel.dk
Subject: Re: [PATCH 0/2] radix-tree: fix writeback livelock avoidance code
Date: Sat, 21 Aug 2010 00:29:06 +1000 [thread overview]
Message-ID: <20100820142906.GD31488@dastard> (raw)
In-Reply-To: <20100820135141.GC5716@quack.suse.cz>
On Fri, Aug 20, 2010 at 03:51:41PM +0200, Jan Kara wrote:
> On Fri 20-08-10 15:22:05, Dave Chinner wrote:
> > The following two patches fix bugs in the new radix tree functionality used to
> > implement the writeback livelock avoidance code. Both bugs manifest themselves
> > as stray PAGECACHE_TAG_TOWRITE tags in the mapping->page_tree radix tree
> > resulting in livelocks during tag lookups. More subtly, they also appear to
> > result in writeback tree walks occasionally terminating early and so not
> > actually writing all the pages they are supposed to.
> Really, how that early termination could happen? I'm just wondering
> because I don't see that.. The code just mindlessly copies tags regardless
> of how target flags are set so that's why I'd think that any stale copied
> flags just don't matter...
With the debug I had in pace, I saw a couple of find_get_pages_tag
loops stop (nr_found == 0) rather than livelock when they
encountered a stray tag, which appears to result in writeback not
writing all the pages. I also saw invalidation removing pages from
the page cache that had the PAGECACHE_TAG_TOWRITE tag set, which
indicated that sometimes they weren't getting written back as they
should have been. These were quite rare - they maybe occurred once
for every 1000 livelock occurrences I saw....
Cheers,
Dave.
--
Dave Chinner
david@fromorbit.com
next prev parent reply other threads:[~2010-08-20 14:29 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-08-20 5:22 [PATCH 0/2] radix-tree: fix writeback livelock avoidance code Dave Chinner
2010-08-20 5:22 ` [PATCH 1/2] radix-tree: clear all tags in radix_tree_node_rcu_free Dave Chinner
2010-08-20 8:00 ` Nick Piggin
2010-08-20 13:00 ` Jan Kara
2010-08-20 5:22 ` [PATCH 2/2] radix-tree: radix_tree_range_tag_if_tagged() can set incorrect tags Dave Chinner
2010-08-20 8:02 ` Nick Piggin
2010-08-20 13:39 ` Jan Kara
2010-08-20 13:51 ` [PATCH 0/2] radix-tree: fix writeback livelock avoidance code Jan Kara
2010-08-20 14:29 ` Dave Chinner [this message]
2010-08-25 20:11 ` Jan Kara
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20100820142906.GD31488@dastard \
--to=david@fromorbit.com \
--cc=jack@suse.cz \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=npiggin@kernel.dk \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).