Re: [PATCH] mm: make faultaround produce old ptes

[Minchan Kim <minchan@kernel.org>]

On Tue, May 17, 2016 at 03:32:46PM +0300, Kirill A. Shutemov wrote:
> Currently, faultaround code produces young pte. This can screw up vmscan
> behaviour[1], as it makes vmscan think that these pages are hot and not
> push them out on first round.
> 
> Let modify faultaround to produce old pte, so they can easily be
> reclaimed under memory pressure.
> 
> This can to some extend defeat purpose of faultaround on machines
> without hardware accessed bit as it will not help up with reducing
> number of minor page faults.
> 
> We may want to disable faultaround on such machines altogether, but
> that's subject for separate patchset.
> 
> [1] https://lkml.kernel.org/r/1460992636-711-1-git-send-email-vinmenon@codeaurora.org
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Cc: Mel Gorman <mgorman@suse.de>
> Cc: Rik van Riel <riel@redhat.com>
> Cc: Michal Hocko <mhocko@kernel.org>
> Cc: Vinayak Menon <vinmenon@codeaurora.org>
> Cc: Minchan Kim <minchan@kernel.org>

I tested 512M mmap sequential word read test on non-HW access bit system
(i.e., ARM) and confirmed it doesn't increase minor fault any more.

= old =
minor fault: 131291
elapsed time: 6747645 usec

= new =
minor fault: 131291
elapsed time: 6709263 usec

0.56% benefit

Acked-by: Minchan Kim <minchan@kernel.org>

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