Commit 9cb937e2 authored Jul 28, 2016 by Minchan Kim Committed by Linus Torvalds Jul 28, 2016

mm, page_alloc: fix dirtyable highmem calculation

When I tested vmscale in mmtest in 32bit, I found the benchmark was slow
down 0.5 times.

                base        node
                   1    global-1
User           12.98       16.04
System        147.61      166.42
Elapsed        26.48       38.08

With vmstat, I found IO wait avg is much increased compared to base.

The reason was highmem_dirtyable_memory accumulates free pages and
highmem_file_pages from HIGHMEM to MOVABLE zones which was wrong.  With
that, dirth_thresh in throtlle_vm_write is always 0 so that it calls
congestion_wait frequently if writeback starts.

With this patch, it is much recovered.

                base        node          fi
                   1    global-1         fix
User           12.98       16.04       13.78
System        147.61      166.42      143.92
Elapsed        26.48       38.08       29.64

Link: http://lkml.kernel.org/r/1468404004-5085-4-git-send-email-mgorman@techsingularity.net


Signed-off-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent bca67592

mm/page-writeback.c

+10 −6

Original line number	Diff line number	Diff line
		@@ -307,27 +307,31 @@ static unsigned long highmem_dirtyable_memory(unsigned long total)
		{
		#ifdef CONFIG_HIGHMEM
		int node;
		unsigned long x = 0;
		unsigned long x;
		int i;
		unsigned long dirtyable = atomic_read(&highmem_file_pages);
		unsigned long dirtyable = 0;

		for_each_node_state(node, N_HIGH_MEMORY) {
		for (i = ZONE_NORMAL + 1; i < MAX_NR_ZONES; i++) {
		struct zone *z;
		unsigned long nr_pages;

		if (!is_highmem_idx(i))
		continue;

		z = &NODE_DATA(node)->node_zones[i];
		dirtyable += zone_page_state(z, NR_FREE_PAGES);
		if (!populated_zone(z))
		continue;

		nr_pages = zone_page_state(z, NR_FREE_PAGES);
		/* watch for underflows */
		dirtyable -= min(dirtyable, high_wmark_pages(z));

		x += dirtyable;
		nr_pages -= min(nr_pages, high_wmark_pages(z));
		dirtyable += nr_pages;
		}
		}

		x = dirtyable + atomic_read(&highmem_file_pages);

		/*
		* Unreclaimable memory (kernel memory or anonymous memory
		* without swap) can bring down the dirtyable pages below

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