On Thu, Aug 19, 2010 at 11:47:03PM +0900, Minchan Kim wrote:
> On Mon, Aug 16, 2010 at 10:42:13AM +0100, Mel Gorman wrote:
> > When under significant memory pressure, a process enters direct reclaim
> > and immediately afterwards tries to allocate a page. If it fails and no
> > further progress is made, it's possible the system will go OOM. However,
> > on systems with large amounts of memory, it's possible that a significant
> > number of pages are on per-cpu lists and inaccessible to the calling
> > process. This leads to a process entering direct reclaim more often than
> > it should increasing the pressure on the system and compounding the problem.
> >
> > This patch notes that if direct reclaim is making progress but
> > allocations are still failing that the system is already under heavy
> > pressure. In this case, it drains the per-cpu lists and tries the
> > allocation a second time before continuing.
> >
> > Signed-off-by: Mel Gorman <mel@xxxxxxxxx>
> > ---
> > mm/page_alloc.c | 19 +++++++++++++++++--
> > 1 files changed, 17 insertions(+), 2 deletions(-)
> >
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 67a2ed0..a8651a4 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -1844,6 +1844,7 @@ __alloc_pages_direct_reclaim(gfp_t gfp_mask, unsigned int order,
> > struct page *page = NULL;
> > struct reclaim_state reclaim_state;
> > struct task_struct *p = current;
> > + bool drained = false;
> >
> > cond_resched();
> >
> > @@ -1865,11 +1866,25 @@ __alloc_pages_direct_reclaim(gfp_t gfp_mask, unsigned int order,
> > if (order != 0)
> > drain_all_pages();
> >
>
> Nitpick:
>
> How about removing above condition and drain_all_pages?
> If get_page_from_freelist fails, we do drain_all_pages at last.
> It can remove double calling of drain_all_pagse in case of order > 0.
> In addition, if the VM can't reclaim anythings, we don't need to drain
> in case of order > 0.
>
That sounds reasonable. V2 of this series will delete the lines
if (order != 0)
drain_all_pages()
>
> > - if (likely(*did_some_progress))
> > - page = get_page_from_freelist(gfp_mask, nodemask, order,
> > + if (unlikely(!(*did_some_progress)))
> > + return NULL;
> > +
> > +retry:
> > + page = get_page_from_freelist(gfp_mask, nodemask, order,
> > zonelist, high_zoneidx,
> > alloc_flags, preferred_zone,
> > migratetype);
> > +
> > + /*
> > + * If an allocation failed after direct reclaim, it could be because
> > + * pages are pinned on the per-cpu lists. Drain them and try again
> > + */
> > + if (!page && !drained) {
> > + drain_all_pages();
> > + drained = true;
> > + goto retry;
> > + }
> > +
> > return page;
> > }
> >
> > --
> > 1.7.1
> >
--
Mel Gorman
Part-time Phd Student Linux Technology Center
University of Limerick IBM Dublin Software Lab
--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@xxxxxxxxxx For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>