[PATCH] mm: pcp use non powers of 2 for batch size
Jack Steiner reported this to have fixed his problem (bad colouring): "The patches fix both problems that I found - bad coloring & excessive pages in pagesets." In most workloads this is not likely to be such a pronounced problem, however it should help corner cases. And avoiding powers of 2 in these types of memory operations is always a good idea. Signed-off-by: Nick Piggin <nickpiggin@yahoo.com.au> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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@ -1671,6 +1671,18 @@ static void __init free_area_init_core(struct pglist_data *pgdat,
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if (batch < 1)
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if (batch < 1)
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batch = 1;
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batch = 1;
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/*
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* Clamp the batch to a 2^n - 1 value. Having a power
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* of 2 value was found to be more likely to have
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* suboptimal cache aliasing properties in some cases.
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*
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* For example if 2 tasks are alternately allocating
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* batches of pages, one task can end up with a lot
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* of pages of one half of the possible page colors
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* and the other with pages of the other colors.
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*/
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batch = (1 << fls(batch + batch/2)) - 1;
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for (cpu = 0; cpu < NR_CPUS; cpu++) {
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for (cpu = 0; cpu < NR_CPUS; cpu++) {
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struct per_cpu_pages *pcp;
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struct per_cpu_pages *pcp;
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