Commit 8e30f272 authored by Nick Piggin's avatar Nick Piggin Committed by Linus Torvalds
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[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: default avatarNick Piggin <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 81b4082d
......@@ -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;
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