From: Jamie Lokier <jamie@shareable.org>
To: Christoph Hellwig <hch@infradead.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
Jens Axboe <jens.axboe@oracle.com>,
linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
chris.mason@oracle.com, david@fromorbit.com, tytso@mit.edu,
akpm@linux-foundation.org, jack@suse.cz
Subject: Re: [PATCH 8/8] vm: Add an tuning knob for vm.max_writeback_pages
Date: Wed, 2 Sep 2009 00:52:18 +0100 [thread overview]
Message-ID: <20090901235218.GC1321@shareable.org> (raw)
In-Reply-To: <20090901184455.GA27294@infradead.org>
Christoph Hellwig wrote:
> On Tue, Sep 01, 2009 at 08:38:55PM +0200, Peter Zijlstra wrote:
> > Do we really need a tunable for this?
>
> It will make increasing it in the field a lot easier. And having deal
> with really large systems I have the fear that there are I/O topologies
> outhere for which every "reasonable" value is too low.
>
> > I guess we need a limit to avoid it writing out everything, but can't we
> > have something automagic?
>
> Some automatic adjustment would be nice. But finding the right auto
> tuning will be an interesting exercise.
I have embedded systems with 32MB RAM and no MMU, where I deliberately
make the equivalent of max_writeback_pages *smaller* to limit the
number of dirty pages causing fragmentation and preventing allocation
of high-order pages... Write performance is less important than being
able to allocate contiguous memory for reads.
They are still using 2.4 kernels, but the principle still applies.
maybe even more on 2.6 which is more prone to fragmentation on small
no-MMU devices.
-- Jamie
next prev parent reply other threads:[~2009-09-01 23:52 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-09-01 11:18 [PATCH 0/8] Per-bdi writeback flusher threads v16 Jens Axboe
2009-09-01 11:18 ` [PATCH 1/8] writeback: move super_block argument to struct writeback_control Jens Axboe
2009-09-01 11:55 ` Theodore Tso
2009-09-01 11:57 ` Theodore Tso
2009-09-01 12:05 ` Jens Axboe
2009-09-01 14:06 ` Theodore Tso
2009-09-01 21:51 ` Christoph Hellwig
2009-09-02 6:45 ` Jens Axboe
2009-09-01 11:19 ` [PATCH 2/8] writeback: move dirty inodes from super_block to backing_dev_info Jens Axboe
2009-09-01 11:19 ` [PATCH 3/8] writeback: switch to per-bdi threads for flushing data Jens Axboe
2009-09-01 11:19 ` [PATCH 4/8] writeback: get rid of pdflush completely Jens Axboe
2009-09-01 11:19 ` [PATCH 5/8] writeback: add some debug inode list counters to bdi stats Jens Axboe
2009-09-01 11:19 ` [PATCH 6/8] writeback: add name to backing_dev_info Jens Axboe
2009-09-01 11:19 ` [PATCH 7/8] writeback: check for registered bdi in flusher add and inode dirty Jens Axboe
2009-09-01 11:19 ` [PATCH 8/8] vm: Add an tuning knob for vm.max_writeback_pages Jens Axboe
2009-09-01 18:38 ` Peter Zijlstra
2009-09-01 18:44 ` Christoph Hellwig
2009-09-01 20:27 ` Theodore Tso
2009-09-02 7:32 ` Peter Zijlstra
2009-09-02 7:35 ` Peter Zijlstra
2009-09-01 23:52 ` Jamie Lokier [this message]
2009-09-01 23:56 ` Jamie Lokier
-- strict thread matches above, loose matches on Subject: below --
2009-09-02 8:42 [PATCH 0/8] Per-bdi writeback flusher threads v17 Jens Axboe
2009-09-02 8:42 ` [PATCH 8/8] vm: Add an tuning knob for vm.max_writeback_pages Jens Axboe
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