linux-kernel - Re: [PATCH] swap: send callback when swap slot is freed

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Message-ID: <Pine.LNX.4.64.0908131836270.14631@sister.anvils>
Date:	Thu, 13 Aug 2009 18:45:18 +0100 (BST)
From:	Hugh Dickins <hugh.dickins@...cali.co.uk>
To:	Nitin Gupta <ngupta@...are.org>
cc:	Matthew Wilcox <willy@...ux.intel.com>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] swap: send callback when swap slot is freed

On Thu, 13 Aug 2009, Nitin Gupta wrote:
> On 08/13/2009 04:18 AM, Hugh Dickins wrote:
> 
> > But fundamentally, though I can see how this cutdown communication
> > path is useful to compcache, I'd much rather deal with it by the more
> > general discard route if we can.
> 
> I tried this too -- make discard bio request as soon as a swap slot becomes
> free (I can send details if you want). However, I could not get it to work.

I'll send you an updated version of what I experimented with eight
months ago: but changes in the swap_map count handling since then
mean that it might need some subtle adjustments - I'll need to go
over it carefully and retest before sending you.

(But that won't be a waste of my time: I shall soon need to try
that experiment again myself, and I do need to examine those
intervening swap_map count changes more closely.)

> Also, allocating bio to issue discard I/O request looks like a complete
> artifact in compcache case.

Yes, I do understand that feeling.

Hugh
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