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    Subject[PATCH 3/3] mm: page allocator: Drain per-cpu lists after direct reclaim allocation fails
    Date
    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@csn.ul.ie>
    Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
    Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
    Reviewed-by: Christoph Lameter <cl@linux.com>
    ---
    mm/page_alloc.c | 20 ++++++++++++++++----
    1 files changed, 16 insertions(+), 4 deletions(-)

    diff --git a/mm/page_alloc.c b/mm/page_alloc.c
    index bbaa959..750e1dc 100644
    --- a/mm/page_alloc.c
    +++ b/mm/page_alloc.c
    @@ -1847,6 +1847,7 @@ __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();

    @@ -1865,14 +1866,25 @@ __alloc_pages_direct_reclaim(gfp_t gfp_mask, unsigned int order,

    cond_resched();

    - if (order != 0)
    - drain_all_pages();
    + if (unlikely(!(*did_some_progress)))
    + return NULL;

    - if (likely(*did_some_progress))
    - page = get_page_from_freelist(gfp_mask, nodemask, order,
    +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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