linux-kernel - Re: [PATCH 09/11] mm, compaction: Abstract compaction feedback to helpers

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Date:	Wed, 6 Apr 2016 10:46:05 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Hugh Dickins <hughd@...gle.com>
Cc:	Michal Hocko <mhocko@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Mel Gorman <mgorman@...e.de>,
	David Rientjes <rientjes@...gle.com>,
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
	Joonsoo Kim <js1304@...il.com>,
	Hillf Danton <hillf.zj@...baba-inc.com>, linux-mm@...ck.org,
	LKML <linux-kernel@...r.kernel.org>,
	Michal Hocko <mhocko@...e.com>
Subject: Re: [PATCH 09/11] mm, compaction: Abstract compaction feedback to
 helpers

On Tue, 5 Apr 2016 17:55:39 -0700 (PDT) Hugh Dickins <hughd@...gle.com> wrote:

> > I ended up doing this:
> > 
> > 	/* Checks for THP-specific high-order allocations */
> > 	if (!is_thp_allocation(gfp_mask, order))
> > 		migration_mode = MIGRATE_SYNC_LIGHT;
> > 
> > 	/*
> > 	 * Checks for THP-specific high-order allocations and back off
> > 	 * if the the compaction backed off
> > 	 */
> > 	if (is_thp_allocation(gfp_mask) && compaction_withdrawn(compact_result))
> > 		goto nopage;
> 
> You'll already have found that is_thp_allocation() needs the order too.
> But then you had to drop a hunk out of his 10/11 also to fit with mine.
> 
> What you've done may be just right, but I haven't had time to digest
> Michal's changes yet (and not yet seen what happens to the PF_KTHREAD
> distinction), so I think it will probably end up better if you take
> his exactly as he tested and posted them, and drop my 30/31 and 31/31
> for now - I can resubmit them (or maybe drop 30 altogether) after I've
> pondered and tested a little on top of Michal's.
> 
> Huge tmpfs got along fine for many months without 30/31 and 31/31: 30
> is just for experimentation, and 31 to reduce the compaction stalls we
> saw under some loads.  Maybe I'll find that Michal's rework has changed
> the balance there anyway, and something else or nothing at all needed.
> 
> (The gfp_mask stuff was very confusing, and it's painful for me, how
> ~__GFP_KSWAPD_RECLAIM gets used as a secret password to say "THP" and
> how to angle compaction - or maybe it's all more straightforward now.)

OK, thanks.  I dropped
huge-tmpfs-shmem_huge_gfpmask-and-shmem_recovery_gfpmask.patch and
huge-tmpfs-no-kswapd-by-default-on-sync-allocations.patch and restored
Michal's patches.

> Many thanks for giving us both this quick exposure!

I'll push all this into -next later today.