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Date: Thu, 20 Dec 2012 13:29:35 +0400
From: Konstantin Khlebnikov <khlebnikov@openvz.org>
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To: Andrew Morton <akpm@linux-foundation.org>
CC: Hugh Dickins <hughd@google.com>, linux-kernel@vger.kernel.org,
        Mel Gorman <mgorman@suse.de>, Jens Axboe <axboe@kernel.dk>
Subject: Re: [PATCH] mm/swap: add independed bio pool for swap
References: <20121214110118.8387.66431.stgit@zurg> <alpine.LNX.2.00.1212172024500.5927@eggly.anvils> <20121219165343.ccb3a956.akpm@linux-foundation.org>
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Andrew Morton wrote:
> On Mon, 17 Dec 2012 20:45:13 -0800 (PST)
> Hugh Dickins<hughd@google.com>  wrote:
>
>> On Fri, 14 Dec 2012, Konstantin Khlebnikov wrote:
>>
>>> This bio pool guarantees reclaiming progress for anonymous pages.
>>> All avaliable bio in fs_bio_set may be borrowed by writeback which may
>>> never ends, because disk too slow or broken. I have seen this situation in
>>> real life in system where was a lot of bio requests to a loop device which
>>> laying on top of special fuse-based filesystem.
>>
>> Hmm, perhaps, I'm not at all sure.
>
> It probably maybe perhaps makes sense.  Of course, you're screwed if
> one of your swap devices is "disk too slow or broken".
>
> My crystal ball tells me that the 2015 kernel will have a bioset per
> physical device...
>

I predict that they also will be per-cpu. Well... probably maybe we should
just wait for this shining future. I leave this to your discretion...