Re: [PATCH -v2] mm: Don't use radix tree writeback tags for pages in swap cache

From	Michal Hocko <mhocko@kernel.org>
Newsgroups	linux.kernel
Subject	Re: [PATCH -v2] mm: Don't use radix tree writeback tags for pages in swap cache
Date	2016-09-01 11:20 +0200
Message-ID	<scwk9-7Sa-5@gated-at.bofh.it> (permalink)
References	<sbV1g-7PN-7@gated-at.bofh.it> <sc9QB-xQ-11@gated-at.bofh.it> <scloK-7GT-17@gated-at.bofh.it>
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On Wed 31-08-16 14:30:31, Andrew Morton wrote:
> On Wed, 31 Aug 2016 10:14:59 +0100 Mel Gorman <mgorman@techsingularity.net> wrote:
> 
> > >    2506952 __  2%     +28.1%    3212076 __  7%  vm-scalability.throughput
> > >    1207402 __  7%     +22.3%    1476578 __  6%  vmstat.swap.so
> > >      10.86 __ 12%     -23.4%       8.31 __ 16%  perf-profile.cycles-pp._raw_spin_lock_irq.__add_to_swap_cache.add_to_swap_cache.add_to_swap.shrink_page_list
> > >      10.82 __ 13%     -33.1%       7.24 __ 14%  perf-profile.cycles-pp._raw_spin_lock_irqsave.__remove_mapping.shrink_page_list.shrink_inactive_list.shrink_zone_memcg
> > >      10.36 __ 11%    -100.0%       0.00 __ -1%  perf-profile.cycles-pp._raw_spin_lock_irqsave.__test_set_page_writeback.bdev_write_page.__swap_writepage.swap_writepage
> > >      10.52 __ 12%    -100.0%       0.00 __ -1%  perf-profile.cycles-pp._raw_spin_lock_irqsave.test_clear_page_writeback.end_page_writeback.page_endio.pmem_rw_page
> > > 
> > 
> > I didn't see anything wrong with the patch but it's worth highlighting
> > that this hunk means we are now out of GFP bits.
> 
> Well ugh.  What are we to do about that?

Can we simply give these AS_ flags their own word in mapping rather than
squash them together with gfp flags and impose the restriction on the
number of gfp flags. There was some demand for new gfp flags already and
mapping flags were in the way.
-- 
Michal Hocko
SUSE Labs

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[PATCH -v2] mm: Don't use radix tree writeback tags for pages in swap cache "Huang, Ying" <ying.huang@intel.com> - 2016-08-30 19:30 +0200
  Re: [PATCH -v2] mm: Don't use radix tree writeback tags for pages  in swap cache Rik van Riel <riel@redhat.com> - 2016-08-30 20:40 +0200
  Re: [PATCH -v2] mm: Don't use radix tree writeback tags for pages in  swap cache Mel Gorman <mgorman@techsingularity.net> - 2016-08-31 11:20 +0200
    Re: [PATCH -v2] mm: Don't use radix tree writeback tags for pages in swap cache "Huang\, Ying" <ying.huang@intel.com> - 2016-08-31 17:20 +0200
      Re: [PATCH -v2] mm: Don't use radix tree writeback tags for pages in  swap cache Mel Gorman <mgorman@techsingularity.net> - 2016-08-31 17:40 +0200
        Re: [PATCH -v2] mm: Don't use radix tree writeback tags for pages in swap cache "Huang\, Ying" <ying.huang@intel.com> - 2016-08-31 17:50 +0200
        Re: [PATCH -v2] mm: Don't use radix tree writeback tags for pages in swap cache Andi Kleen <andi@firstfloor.org> - 2016-08-31 23:40 +0200
    Re: [PATCH -v2] mm: Don't use radix tree writeback tags for pages  in swap cache Andrew Morton <akpm@linux-foundation.org> - 2016-08-31 23:40 +0200
      Re: [PATCH -v2] mm: Don't use radix tree writeback tags for pages in  swap cache Mel Gorman <mgorman@techsingularity.net> - 2016-09-01 11:00 +0200
      Re: [PATCH -v2] mm: Don't use radix tree writeback tags for pages in  swap cache Michal Hocko <mhocko@kernel.org> - 2016-09-01 11:20 +0200

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