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

[Minchan Kim <minchan@kernel.org>]

On Wed, May 18, 2016 at 10:22:59AM +0900, Minchan Kim wrote:
> 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>

Oops, label was wrong.

I meant

old : 4096 fault_around
new : 65536 fault_around

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>