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

From: Shaohua Li
Date: Tue Oct 23 2012 - 21:14:01 EST

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.

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