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    SubjectRe: [PATCH v3 5/5] mm: Only IPI CPUs to drain local pages if they exist
    On Sun, 13 Nov 2011, Gilad Ben-Yossef wrote:

    > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
    > index 9dd443d..44dc6c5 100644
    > --- a/mm/page_alloc.c
    > +++ b/mm/page_alloc.c
    > @@ -1119,7 +1119,23 @@ void drain_local_pages(void *arg)
    > */
    > void drain_all_pages(void)
    > {
    > - on_each_cpu(drain_local_pages, NULL, 1);
    > + int cpu;
    > + struct zone *zone;
    > + cpumask_var_t cpus;
    > + struct per_cpu_pageset *pageset;

    We usually name such pointers "pcp" in the page allocator.

    > +
    > + if (likely(zalloc_cpumask_var(&cpus, GFP_ATOMIC))) {
    > + for_each_populated_zone(zone) {
    > + for_each_online_cpu(cpu) {
    > + pageset = per_cpu_ptr(zone->pageset, cpu);
    > + if (pageset->pcp.count)
    > + cpumask_set_cpu(cpu, cpus);
    > + }

    The pagesets are allocated on bootup from the per cpu areas. You may get a
    better access pattern by using for_each_online_cpu as the outer loop
    because their is a likelyhood of linear increasing accesses as you loop
    through the zones for a particular cpu.

    Acked-by: Christoph Lameter <cl@linux.com>



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