linux-kernel - Re: [PATCH RFC] mm/swap: automatic tuning for swapin readahead

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Date:	Tue, 6 Nov 2012 13:36:28 +0800
From:	Shaohua Li <shli@...nel.org>
To:	Rik van Riel <riel@...hat.com>, Hugh Dickins <hughd@...gle.com>
Cc:	Konstantin Khlebnikov <khlebnikov@...nvz.org>,
	Minchan Kim <minchan@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Wu Fengguang <fengguang.wu@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH RFC] mm/swap: automatic tuning for swapin readahead

On Wed, Oct 24, 2012 at 09:13:56AM +0800, Shaohua Li wrote:
> On Tue, Oct 23, 2012 at 09:41:00AM -0400, Rik van Riel wrote:
> > On 10/23/2012 01:51 AM, Shaohua Li wrote:
> > 
> > >I have no strong point against the global state method. But I'd agree making the
> > >heuristic simple is preferred currently. I'm happy about the patch if the '+1'
> > >is removed.
> > 
> > Without the +1, how will you figure out when to re-enable readahead?
> 
> Below code in swapin_nr_pages can recover it.
> +               if (offset == prev_offset + 1 || offset == prev_offset - 1)
> +                       pages <<= 1;
> 
> Not perfect, but should work in some sort. This reminds me to think if
> pagereadahead flag is really required, hit in swap cache is a more reliable way
> to count readahead hit, and as Hugh mentioned, swap isn't vma bound.

Hugh,
ping! Any chance you can check this again?

Thanks,
Shaohua
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