Date: Wed, 20 Jun 2007 11:14:04 +0200
From: Jens Axboe <jens.axboe@oracle.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>, davej@redhat.com,
       tim.c.chen@linux.intel.com, linux-kernel@vger.kernel.org,
       torvalds@linux-foundation.org
Subject: Re: Change in default vm_dirty_ratio
Message-ID: <20070620091404.GO18863@kernel.dk>
References: <1182201271.4883.22.camel@localhost.localdomain> <20070618164711.9de1c38e.akpm@linux-foundation.org> <20070620042434.GC12096@redhat.com> <20070619214407.dfff0ca6.akpm@linux-foundation.org> <1182328536.21117.24.camel@twins> <20070620015826.03f1d71a.akpm@linux-foundation.org>
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On Wed, Jun 20 2007, Andrew Morton wrote:
> Perhaps our queues are too long - if the VFS _does_ back off, it'll take
> some time for that to have an effect.
> 
> Perhaps the fact that the queue size knows nothing about the _size_ of the
> requests in the queue is a problem.

It's complicated, the size may not matter a lot. 128 sequential 512kb IO
may complete faster than 128 random 4kb IO's.

> Back away even further here.
> 
> What user-visible problem(s) are we attemping to fix?

I'd like innocent-app-doing-little-write-or-fsync not being stalled by
big-bad-app-doing-lots-of-dirtying.

-- 
Jens Axboe

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