From: Nick Piggin Date: Sun, 1 May 2005 15:58:36 +0000 (-0700) Subject: [PATCH] mm: pcp use non powers of 2 for batch size X-Git-Url: http://git.cdn.openwrt.org/?a=commitdiff_plain;h=8e30f272a93ec9c1d5c305c5040dfaebc880499d;p=openwrt%2Fstaging%2Fblogic.git [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 Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/mm/page_alloc.c b/mm/page_alloc.c index c73dbbc1cd8f..08e8627361a0 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -1671,6 +1671,18 @@ static void __init free_area_init_core(struct pglist_data *pgdat, if (batch < 1) batch = 1; + /* + * Clamp the batch to a 2^n - 1 value. Having a power + * of 2 value was found to be more likely to have + * suboptimal cache aliasing properties in some cases. + * + * For example if 2 tasks are alternately allocating + * batches of pages, one task can end up with a lot + * of pages of one half of the possible page colors + * and the other with pages of the other colors. + */ + batch = (1 << fls(batch + batch/2)) - 1; + for (cpu = 0; cpu < NR_CPUS; cpu++) { struct per_cpu_pages *pcp;