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    Subject[PATCH 1/4] Properly account for the number of page cache pages zone_reclaim() can reclaim
    Date
    On NUMA machines, the administrator can configure zone_reclaim_mode that
    is a more targetted form of direct reclaim. On machines with large NUMA
    distances for example, a zone_reclaim_mode defaults to 1 meaning that clean
    unmapped pages will be reclaimed if the zone watermarks are not being met.

    There is a heuristic that determines if the scan is worthwhile but the
    problem is that the heuristic is not being properly applied and is basically
    assuming zone_reclaim_mode is 1 if it is enabled.

    Historically, once enabled it was depending on NR_FILE_PAGES which may
    include swapcache pages that the reclaim_mode cannot deal with. Patch
    vmscan-change-the-number-of-the-unmapped-files-in-zone-reclaim.patch by
    Kosaki Motohiro noted that zone_page_state(zone, NR_FILE_PAGES) included
    pages that were not file-backed such as swapcache and made a calculation
    based on the inactive, active and mapped files. This is far superior
    when zone_reclaim==1 but if RECLAIM_SWAP is set, then NR_FILE_PAGES is a
    reasonable starting figure.

    This patch alters how zone_reclaim() works out how many pages it might be
    able to reclaim given the current reclaim_mode. If RECLAIM_SWAP is set
    in the reclaim_mode it will either consider NR_FILE_PAGES as potential
    candidates or else use NR_{IN}ACTIVE}_PAGES-NR_FILE_MAPPED to discount
    swapcache and other non-file-backed pages. If RECLAIM_WRITE is not set,
    then NR_FILE_DIRTY number of pages are not candidates. If RECLAIM_SWAP is
    not set, then NR_FILE_MAPPED are not.

    Signed-off-by: Mel Gorman <mel@csn.ul.ie>
    Acked-by: Christoph Lameter <cl@linux-foundation.org>
    ---
    mm/vmscan.c | 52 ++++++++++++++++++++++++++++++++++++++--------------
    1 files changed, 38 insertions(+), 14 deletions(-)

    diff --git a/mm/vmscan.c b/mm/vmscan.c
    index 2ddcfc8..2bfc76e 100644
    --- a/mm/vmscan.c
    +++ b/mm/vmscan.c
    @@ -2333,6 +2333,41 @@ int sysctl_min_unmapped_ratio = 1;
    */
    int sysctl_min_slab_ratio = 5;

    +static inline unsigned long zone_unmapped_file_pages(struct zone *zone)
    +{
    + return zone_page_state(zone, NR_INACTIVE_FILE) +
    + zone_page_state(zone, NR_ACTIVE_FILE) -
    + zone_page_state(zone, NR_FILE_MAPPED);
    +}
    +
    +/* Work out how many page cache pages we can reclaim in this reclaim_mode */
    +static inline long zone_pagecache_reclaimable(struct zone *zone)
    +{
    + long nr_pagecache_reclaimable;
    + long delta = 0;
    +
    + /*
    + * If RECLAIM_SWAP is set, then all file pages are considered
    + * potentially reclaimable. Otherwise, we have to worry about
    + * pages like swapcache and zone_unmapped_file_pages() provides
    + * a better estimate
    + */
    + if (zone_reclaim_mode & RECLAIM_SWAP)
    + nr_pagecache_reclaimable = zone_page_state(zone, NR_FILE_PAGES);
    + else
    + nr_pagecache_reclaimable = zone_unmapped_file_pages(zone);
    +
    + /* If we can't clean pages, remove dirty pages from consideration */
    + if (!(zone_reclaim_mode & RECLAIM_WRITE))
    + delta += zone_page_state(zone, NR_FILE_DIRTY);
    +
    + /* Beware of double accounting */
    + if (delta < nr_pagecache_reclaimable)
    + nr_pagecache_reclaimable -= delta;
    +
    + return nr_pagecache_reclaimable;
    +}
    +
    /*
    * Try to free up some pages from this zone through reclaim.
    */
    @@ -2355,7 +2390,6 @@ static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
    .isolate_pages = isolate_pages_global,
    };
    unsigned long slab_reclaimable;
    - long nr_unmapped_file_pages;

    disable_swap_token();
    cond_resched();
    @@ -2368,11 +2402,7 @@ static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
    reclaim_state.reclaimed_slab = 0;
    p->reclaim_state = &reclaim_state;

    - nr_unmapped_file_pages = zone_page_state(zone, NR_INACTIVE_FILE) +
    - zone_page_state(zone, NR_ACTIVE_FILE) -
    - zone_page_state(zone, NR_FILE_MAPPED);
    -
    - if (nr_unmapped_file_pages > zone->min_unmapped_pages) {
    + if (zone_pagecache_reclaimable(zone) > zone->min_unmapped_pages) {
    /*
    * Free memory by calling shrink zone with increasing
    * priorities until we have enough memory freed.
    @@ -2419,8 +2449,6 @@ int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
    {
    int node_id;
    int ret;
    - long nr_unmapped_file_pages;
    - long nr_slab_reclaimable;

    /*
    * Zone reclaim reclaims unmapped file backed pages and
    @@ -2432,12 +2460,8 @@ int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
    * if less than a specified percentage of the zone is used by
    * unmapped file backed pages.
    */
    - nr_unmapped_file_pages = zone_page_state(zone, NR_INACTIVE_FILE) +
    - zone_page_state(zone, NR_ACTIVE_FILE) -
    - zone_page_state(zone, NR_FILE_MAPPED);
    - nr_slab_reclaimable = zone_page_state(zone, NR_SLAB_RECLAIMABLE);
    - if (nr_unmapped_file_pages <= zone->min_unmapped_pages &&
    - nr_slab_reclaimable <= zone->min_slab_pages)
    + if (zone_pagecache_reclaimable(zone) <= zone->min_unmapped_pages &&
    + zone_page_state(zone, NR_SLAB_RECLAIMABLE) <= zone->min_slab_pages)
    return 0;

    if (zone_is_all_unreclaimable(zone))
    --
    1.5.6.5


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