Re: [RFC][PATCH] mm: the page of MIGRATE_RESERVE don't insert into pcp

KAMEZAWA Hiroyuki
2008-11-07T01:43:20Z

On Thu, 6 Nov 2008 16:46:45 +0000
Mel Gorman <mel@csn.ul.ie> wrote:
> > otherwise, the system have unnecessary memory starvation risk
> > because other cpu can't use this emergency pages.
> >
> >
> >
> > Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
> > CC: Mel Gorman <mel@csn.ul.ie>
> > CC: Christoph Lameter <cl@linux-foundation.org>
> >
>
> This patch seems functionally sound but as Christoph points out, this
> adds another branch to the fast path. Now, I ran some tests and those that
> completed didn't show any problems but adding branches in the fast path can
> eventually lead to hard-to-detect performance problems.
>
dividing pcp-list into MIGRATE_TYPES is bad ?
If divided, we can get rid of scan.

Thanks,
-Kame

> Do you have a situation in mind that this patch fixes up?
>
> Thanks
>
> > ---
> > mm/page_alloc.c | 12 +++++++++++-
> > 1 file changed, 11 insertions(+), 1 deletion(-)
> >
> > Index: b/mm/page_alloc.c
> > ===================================================================
> > --- a/mm/page_alloc.c 2008-11-06 06:01:15.000000000 +0900
> > +++ b/mm/page_alloc.c 2008-11-06 06:27:41.000000000 +0900
> > @@ -1002,6 +1002,7 @@ static void free_hot_cold_page(struct pa
> > struct zone *zone = page_zone(page);
> > struct per_cpu_pages *pcp;
> > unsigned long flags;
> > + int migratetype = get_pageblock_migratetype(page);
> >
> > if (PageAnon(page))
> > page->mapping = NULL;
> > @@ -1018,16 +1019,25 @@ static void free_hot_cold_page(struct pa
> > pcp = &zone_pcp(zone, get_cpu())->pcp;
> > local_irq_save(flags);
> > __count_vm_event(PGFREE);
> > +
> > + set_page_private(page, migratetype);
> > +
> > + /* the page for emergency shouldn't be cached */
> > + if (migratetype == MIGRATE_RESERVE) {
> > + free_one_page(zone, page, 0);
> > + goto out;
> > + }
> > if (cold)
> > list_add_tail(&page->lru, &pcp->list);
> > else
> > list_add(&page->lru, &pcp->list);
> > - set_page_private(page, get_pageblock_migratetype(page));
> > pcp->count++;
> > if (pcp->count >= pcp->high) {
> > free_pages_bulk(zone, pcp->batch, &pcp->list, 0);
> > pcp->count -= pcp->batch;
> > }
> > +
> > +out:
> > local_irq_restore(flags);
> > put_cpu();
> > }
> >
> >
>
> --
> Mel Gorman
> Part-time Phd Student Linux Technology Center
> University of Limerick IBM Dublin Software Lab
>
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