From: Jan Kara <jack@suse.cz>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Jan Kara <jack@suse.cz>, LKML <linux-kernel@vger.kernel.org>,
npiggin@suse.de, fengguang.wu@intel.com
Subject: Re: [PATCH 2/3] mm: Implement writeback livelock avoidance using page tagging
Date: Mon, 15 Feb 2010 16:47:51 +0100 [thread overview]
Message-ID: <20100215154751.GG3434@quack.suse.cz> (raw)
In-Reply-To: <20100212113955.4c023130.akpm@linux-foundation.org>
On Fri 12-02-10 11:39:55, Andrew Morton wrote:
> On Fri, 12 Feb 2010 00:06:23 +0100
> Jan Kara <jack@suse.cz> wrote:
>
> > The idea is simple: Tag all pages that should be written back
> > with a special tag (TOWRITE) in the radix tree. This can be done
> > rather quickly and thus livelocks should not happen in practice.
> > Then we start doing the hard work of locking pages and sending
> > them to disk only for those pages that have TOWRITE tag set.
>
> Adding a second pass across all the pages sounds expensive?
Strictly speaking it's just through the radix tree and only through
branches with DIRTY_TAG set. But yes, there is some additional CPU cost.
I just thought that given the total cost of submitting a page it is
an acceptable increase and the simplification is worth it.
Would some numbers make you happier? Any suggestion for measurements?
Because I think that even for writes to tmpfs the change will be lost
in the noise...
Honza
--
Jan Kara <jack@suse.cz>
SUSE Labs, CR
next prev parent reply other threads:[~2010-02-15 15:47 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-02-11 23:06 [RFC] [PATCH 0/3] Writeback livelock avoidance using page tags (v2) Jan Kara
2010-02-11 23:06 ` [PATCH 1/3] radix-tree: Implement function radix_tree_gang_tag_if_tagged Jan Kara
2010-02-15 16:01 ` Nick Piggin
2010-02-11 23:06 ` [PATCH 2/3] mm: Implement writeback livelock avoidance using page tagging Jan Kara
2010-02-12 19:39 ` Andrew Morton
2010-02-15 15:47 ` Jan Kara [this message]
2010-02-15 16:21 ` Nick Piggin
2010-02-15 16:24 ` Christoph Hellwig
2010-02-15 16:37 ` Nick Piggin
2010-02-15 19:57 ` Jan Kara
2010-02-16 14:19 ` Nick Piggin
2010-02-11 23:06 ` [PATCH 3/3] mm: Debugging of new livelock avoidance Jan Kara
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