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Date: Wed, 24 Oct 2012 09:13:56 +0800
From: Shaohua Li <shli@kernel.org>
To: Rik van Riel <riel@redhat.com>
Cc: Hugh Dickins <hughd@google.com>,
        Konstantin Khlebnikov <khlebnikov@openvz.org>,
        Minchan Kim <minchan@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
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        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>
Subject: Re: [PATCH RFC] mm/swap: automatic tuning for swapin readahead
Message-ID: <20121024011356.GA6400@kernel.org>
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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.

Thanks,
Shaohua