linux-kernel - Re: [PATCH 4/6] writeback: dont redirty tail an inode with dirty pages

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Mon, 12 Jul 2010 15:13:17 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Wu Fengguang <fengguang.wu@...el.com>
Cc:	Dave Chinner <david@...morbit.com>,
	Christoph Hellwig <hch@...radead.org>, Jan Kara <jack@...e.cz>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	Linux Memory Management List <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/6] writeback: dont redirty tail an inode with dirty
 pages

On Mon, 12 Jul 2010 23:31:27 +0800
Wu Fengguang <fengguang.wu@...el.com> wrote:

> > > +		} else if (inode->i_state & I_DIRTY) {
> > > +			/*
> > > +			 * At least XFS will redirty the inode during the
> > > +			 * writeback (delalloc) and on io completion (isize).
> > > +			 */
> > > +			redirty_tail(inode);
> > 
> > I'd drop the mention of XFS here - any filesystem that does delayed
> > allocation or unwritten extent conversion after Io completion will
> > cause this. Perhaps make the comment:
> > 
> > 	/*
> > 	 * Filesystems can dirty the inode during writeback
> > 	 * operations, such as delayed allocation during submission
> > 	 * or metadata updates after data IO completion.
> > 	 */
> 
> Thanks, comments updated accordingly.
> 
> ---
> writeback: don't redirty tail an inode with dirty pages
> 
> This avoids delaying writeback for an expired (XFS) inode with lots of
> dirty pages, but no active dirtier at the moment. Previously we only do
> that for the kupdate case.
> 

You didn't actually explain the _reason_ for making this change. 
Please always do that.

The patch is...  surprisingly complicated, although the end result
looks OK.  This is not aided by the partial duplication between
mapping_tagged(PAGECACHE_TAG_DIRTY) and I_DIRTY_PAGES.  I don't think
we can easily remove I_DIRTY_PAGES because it's used for the
did-someone-just-dirty-a-page test here.

This code is way too complex and fragile and I fear that anything we do
to it will break something :(

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/