linux-kernel - Re: speeding up swapoff

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Message-ID: <m1d4x52zri.fsf@ebiederm.dsl.xmission.com>
Date:	Thu, 30 Aug 2007 02:27:29 -0600
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Hugh Dickins <hugh@...itas.com>
Cc:	Daniel Drake <ddrake@...ntes3d.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: speeding up swapoff

Hugh Dickins <hugh@...itas.com> writes:

> The speedups I've imagined making, were a need demonstrated, have
> been more on the lines of batching (dealing with a range of pages
> in one go) and hashing (using the swapmap's ushort, so often 1 or
> 2 or 3, to hold an indicator of where to look for its references).

There is one other possibility.  Typically the swap code is using
compatibility disk I/O functions instead of the best the kernel
can offer.  I haven't looked recently but it might be worth just
making certain that there isn't some low-level optimization or
cleanup possible on that path.  Although I may just be thinking
of swapfiles.

I know there were tremendous gains ago when I removed the functions
that wrote pages synchronously to swapfiles.

Eric
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