On Tue, 2007-09-11 at 01:05 +1000, Nick Piggin wrote:
> On Monday 10 September 2007 21:22, Mel Gorman wrote:
> > Per-cpu pages can accidentally cause fragmentation because they are free,
> > but pinned pages in an otherwise contiguous block. When this patch is
> > applied, the per-cpu caches are drained after the direct-reclaim is entered
> > if the requested order is greater than 0. It simply reuses the code used
> > by suspend and hotplug.
>
> Does this help? I have a more general version which could go in
> instead (independently of the anti fragmentation patches).
Yes, it does help. It's noticable when one is trying to get as much
memory in hugepages as possible. It reaches a certain point where
hugepages are free but pinned due to per-cpu pages. This "certain point"
depends on the number of CPUs as a ratio to the size of physical memory
as well as a certain degree of randomness as the location of per-cpu
pages is not predictable. Worst case is not being able to allocate
something like (NR_CPUS * pcp->high * 2) hugepages even if they are
otherwise free.
By all means if you have a general version, send it and I'll take a
look. If it's more general and nicer but still can be used to drain the
per-cpu lists when high-order allocations fail, I'm all for it.
Thanks Nick
> > Signed-off-by: Mel Gorman <[email protected]>
> > Signed-off-by: Andrew Morton <[email protected]>
> > ---
> >
> > mm/page_alloc.c | 24 +++++++++++++++++++++++-
> > 1 file changed, 23 insertions(+), 1 deletion(-)
> >
> > diff -rup -X /usr/src/patchset-0.6/bin//dontdiff
> > linux-2.6.23-rc5-006-group-short-lived-and-reclaimable-kernel-allocations/m
> >m/page_alloc.c
> > linux-2.6.23-rc5-007-drain-per-cpu-lists-when-high-order-allocations-fail/m
> >m/page_alloc.c ---
> > linux-2.6.23-rc5-006-group-short-lived-and-reclaimable-kernel-allocations/m
> >m/page_alloc.c 2007-09-02 16:20:31.000000000 +0100 +++
> > linux-2.6.23-rc5-007-drain-per-cpu-lists-when-high-order-allocations-fail/m
> >m/page_alloc.c 2007-09-02 16:20:48.000000000 +0100 @@ -852,6 +852,7 @@ void
> > mark_free_pages(struct zone *zone)
> > }
> > spin_unlock_irqrestore(&zone->lock, flags);
> > }
> > +#endif /* CONFIG_PM */
> >
> > /*
> > * Spill all of this CPU's per-cpu pages back into the buddy allocator.
> > @@ -864,7 +865,25 @@ void drain_local_pages(void)
> > __drain_pages(smp_processor_id());
> > local_irq_restore(flags);
> > }
> > -#endif /* CONFIG_HIBERNATION */
> > +
> > +void smp_drain_local_pages(void *arg)
> > +{
> > + drain_local_pages();
> > +}
> > +
> > +/*
> > + * Spill all the per-cpu pages from all CPUs back into the buddy allocator
> > + */
> > +void drain_all_local_pages(void)
> > +{
> > + unsigned long flags;
> > +
> > + local_irq_save(flags);
> > + __drain_pages(smp_processor_id());
> > + local_irq_restore(flags);
> > +
> > + smp_call_function(smp_drain_local_pages, NULL, 0, 1);
> > +}
> >
> > /*
> > * Free a 0-order page
> > @@ -1452,6 +1471,9 @@ nofail_alloc:
> >
> > cond_resched();
> >
> > + if (order != 0)
> > + drain_all_local_pages();
> > +
> > if (likely(did_some_progress)) {
> > page = get_page_from_freelist(gfp_mask, order,
> > zonelist, alloc_flags);
-
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