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.
> - 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
>
> --
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--
Kind regards,
Minchan Kim
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