Messages in this thread | | | Date | Mon, 14 May 2012 21:38:02 -0400 | From | KOSAKI Motohiro <> | Subject | Re: [PULL] cpumask: finally make them variable size w/ CPUMASK_OFFSTACK. |
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>> This code still slow than original. when calling reclaim path, new allocation is almost always >> fail. then, your code almost always invoke all cpu batch invalidation. i.e. many ipi. > > I don't know this code. Does that happen often?Do we really need to > optimize the out-of-memory path?
we don't need optimize out-of-memory path. but it's not out-of-memory path. our reclaim code has two steps 1) purge small file cache (try_to_free_pages) 2) get new page (get_page_from_freelist). but if you have smp box, it's racy. To success 1) doesn't guarantee to success 2). then, drain_all_pages() is called frequently than you expected.
> But I should have used on_each_cpu_cond() helper which does this for us > (except it falls back to individial IPIs) which would make this code > neater.
Ah, yes. that definitely makes sense.
>>>> 2) When CONFIG_CPUMASK_OFFSTACK=n and NR_CPUS is relatively large, cpumask on stack may >>>> cause stack overflow. because of, alloc_pages() can be called from >>>> very deep call stack. >>> >>> You can't have large NR_CPUS without CONFIG_CPUMASK_OFFSTACK=y, >>> otherwise you'll get many other stack overflows, too. >> >> Original code put cpumask bss instead stack then. :-) > > Yes, and this is what it looks like if we convert it directly, but I > still don't want to encourage people to do this :( > > Cheers, > Rusty. > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -1179,7 +1179,7 @@ void drain_all_pages(void) > * Allocate in the BSS so we wont require allocation in > * direct reclaim path for CONFIG_CPUMASK_OFFSTACK=y > */ > - static cpumask_t cpus_with_pcps; > + static DECLARE_BITMAP(cpus_with_pcps, NR_CPUS); > > /* > * We don't care about racing with CPU hotplug event > @@ -1197,11 +1197,12 @@ void drain_all_pages(void) > } > } > if (has_pcps) > - cpumask_set_cpu(cpu,&cpus_with_pcps); > + cpumask_set_cpu(cpu, to_cpumask(cpus_with_pcps)); > else > - cpumask_clear_cpu(cpu,&cpus_with_pcps); > + cpumask_clear_cpu(cpu, to_cpumask(cpus_with_pcps)); > } > - on_each_cpu_mask(&cpus_with_pcps, drain_local_pages, NULL, 1); > + on_each_cpu_mask(to_cpumask(cpus_with_pcps), > + drain_local_pages, NULL, 1); > }
Looks good to me. thanks.
Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
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