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    Subject[PATCH 06/17] mm: Only set page->pfmemalloc when ALLOC_NO_WATERMARKS was used
    Date
    __alloc_pages_slowpath() is called when the number of free pages is below
    the low watermark. If the caller is entitled to use ALLOC_NO_WATERMARKS
    then the page will be marked page->pfmemalloc. This protects more pages
    than are strictly necessary as we only need to protect pages allocated
    below the min watermark (the pfmemalloc reserves).

    This patch only sets page->pfmemalloc when ALLOC_NO_WATERMARKS was
    required to allocate the page.

    [rientjes@google.com: David noticed the problem during review]
    Signed-off-by: Mel Gorman <mgorman@suse.de>
    ---
    mm/page_alloc.c | 27 ++++++++++++++-------------
    1 file changed, 14 insertions(+), 13 deletions(-)

    diff --git a/mm/page_alloc.c b/mm/page_alloc.c
    index 3738596..363ca90 100644
    --- a/mm/page_alloc.c
    +++ b/mm/page_alloc.c
    @@ -2043,8 +2043,8 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,

    page = get_page_from_freelist(gfp_mask, nodemask,
    order, zonelist, high_zoneidx,
    - alloc_flags, preferred_zone,
    - migratetype);
    + alloc_flags & ~ALLOC_NO_WATERMARKS,
    + preferred_zone, migratetype);
    if (page) {
    preferred_zone->compact_considered = 0;
    preferred_zone->compact_defer_shift = 0;
    @@ -2124,8 +2124,8 @@ __alloc_pages_direct_reclaim(gfp_t gfp_mask, unsigned int order,
    retry:
    page = get_page_from_freelist(gfp_mask, nodemask, order,
    zonelist, high_zoneidx,
    - alloc_flags, preferred_zone,
    - migratetype);
    + alloc_flags & ~ALLOC_NO_WATERMARKS,
    + preferred_zone, migratetype);

    /*
    * If an allocation failed after direct reclaim, it could be because
    @@ -2296,8 +2296,17 @@ rebalance:
    page = __alloc_pages_high_priority(gfp_mask, order,
    zonelist, high_zoneidx, nodemask,
    preferred_zone, migratetype);
    - if (page)
    + if (page) {
    + /*
    + * page->pfmemalloc is set when ALLOC_NO_WATERMARKS was
    + * necessary to allocate the page. The expectation is
    + * that the caller is taking steps that will free more
    + * memory. The caller should avoid the page being used
    + * for !PFMEMALLOC purposes.
    + */
    + page->pfmemalloc = true;
    goto got_pg;
    + }
    }

    /* Atomic allocations - we can't balance anything */
    @@ -2414,14 +2423,6 @@ nopage:
    warn_alloc_failed(gfp_mask, order, NULL);
    return page;
    got_pg:
    - /*
    - * page->pfmemalloc is set when the caller had PFMEMALLOC set, is
    - * been OOM killed or specified __GFP_MEMALLOC. The expectation is
    - * that the caller is taking steps that will free more memory. The
    - * caller should avoid the page being used for !PFMEMALLOC purposes.
    - */
    - page->pfmemalloc = !!(alloc_flags & ALLOC_NO_WATERMARKS);
    -
    if (kmemcheck_enabled)
    kmemcheck_pagealloc_alloc(page, order, gfp_mask);

    --
    1.7.9.2


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