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Date: Wed, 21 Jun 2006 11:13:35 -0700
From: Martin Bligh <mbligh@google.com>
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To: Nate Diller <nate.diller@gmail.com>
CC: Peter Zijlstra <a.p.zijlstra@chello.nl>, linux-mm@kvack.org,
       linux-kernel@vger.kernel.org, Hugh Dickins <hugh@veritas.com>,
       Andrew Morton <akpm@osdl.org>, David Howells <dhowells@redhat.com>,
       Christoph Lameter <christoph@lameter.com>,
       Nick Piggin <npiggin@suse.de>, Linus Torvalds <torvalds@osdl.org>,
       Hans Reiser <reiser@namesys.com>, "E. Gryaznova" <grev@namesys.com>
Subject: Re: [PATCH] mm/tracking dirty pages: update get_dirty_limits for
 mmap tracking
References: <5c49b0ed0606211001s452c080cu3f55103a130b78f1@mail.gmail.com>
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> -int vm_dirty_ratio = 40;
> +int vm_dirty_ratio = 80;

I don't think you can do that. Because ...

>     unsigned long available_memory = total_pages;
...
> +    dirty = (vm_dirty_ratio * available_memory) / 100;

... there are other things in memory besides pagecache. Limiting
dirty pages to 80% of pagecache might be fine, but not 80%
of total memory.

dirty = (vm_dirty_ratio * (nr_active + nr_inactive)) / 100

might be more sensible. Frankly the whole thing is a crock
anyway, because we should be counting easily freeable clean
pages, not dirty pages, but still.

M.