linux-kernel - Re: [PATCH 31/31] mm, vmstat: Remove zone and node double accounting by approximating retries

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Message-ID: <20160706093338.GO11498@techsingularity.net>
Date:	Wed, 6 Jul 2016 10:33:38 +0100
From:	Mel Gorman <mgorman@...hsingularity.net>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux-MM <linux-mm@...ck.org>, Rik van Riel <riel@...riel.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 31/31] mm, vmstat: Remove zone and node double accounting
 by approximating retries

On Wed, Jul 06, 2016 at 09:58:50AM +0100, Mel Gorman wrote:
> On Wed, Jul 06, 2016 at 09:02:52AM +0900, Minchan Kim wrote:
> > On Fri, Jul 01, 2016 at 09:01:39PM +0100, Mel Gorman wrote:
> > > The number of LRU pages, dirty pages and writeback pages must be accounted
> > > for on both zones and nodes because of the reclaim retry logic, compaction
> > > retry logic and highmem calculations all depending on per-zone stats.
> > > 
> > > The retry logic is only critical for allocations that can use any zones.
> > 
> > Sorry, I cannot follow this assertion.
> > Could you explain?
> > 
> 
> The patch has been reworked since and I tried clarifying the changelog.
> Does this help?
> 

It occurred to me at breakfast that this should be more consistent with
the OOM killer on both 32-bit and 64-bit so;

diff --git a/mm/compaction.c b/mm/compaction.c
index dfe7dafe8e8b..640532831b94 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1448,11 +1448,9 @@ bool compaction_zonelist_suitable(struct alloc_context *ac, int order,
 	struct zoneref *z;
 	pg_data_t *last_pgdat = NULL;
 
-#ifdef CONFIG_HIGHMEM
 	/* Do not retry compaction for zone-constrained allocations */
-	if (!is_highmem_idx(ac->high_zoneidx))
+	if (ac->high_zoneidx < ZONE_NORMAL)
 		return false;
-#endif
 
 	/*
 	 * Make sure at least one zone would pass __compaction_suitable if we continue
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index ded48e580abc..194a8162528b 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3455,11 +3455,11 @@ should_reclaim_retry(gfp_t gfp_mask, unsigned order,
 		return false;
 
 	/*
-	 * Blindly retry allocation requests that cannot use all zones. We do
-	 * not have a reliable and fast means of calculating reclaimable, dirty
-	 * and writeback pages in eligible zones.
+	 * Blindly retry lowmem allocation requests that are often ignored by
+	 * the OOM killer as we not have a reliable and fast means of
+	 * calculating reclaimable, dirty and writeback pages in eligible zones.
 	 */
-	if (IS_ENABLED(CONFIG_HIGHMEM) && !is_highmem_idx(gfp_zone(gfp_mask)))
+	if (ac->high_zoneidx < ZONE_NORMAL)
 		goto out;
 
 	/*