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    SubjectRe: [PATCH 0/7] update checkpatch to v0.29
    On Fri, 21 Aug 2009 22:46:03 +0100
    Andy Whitcroft <apw@canonical.com> wrote:

    > Here is a few update for checkpatch that seem to have gotten lost
    > somewhere along the line, I though you had everything I had queued.
    > These have passed testing here, I have some more stuff in testing and I
    > will get those out soon.
    >
    > This update brings an a number of minor fixes. Thanks for the
    > contributions.

    Running checkpatch 0.29 against the below diff produces a warning spew:

    Use of uninitialized value in length at scripts/checkpatch.pl line 1480.
    Use of uninitialized value in substr at scripts/checkpatch.pl line 1480.
    Use of uninitialized value in substr at scripts/checkpatch.pl line 1480.
    Use of uninitialized value in pattern match (m//) at scripts/checkpatch.pl line 1488.
    Use of uninitialized value in pattern match (m//) at scripts/checkpatch.pl line 1545.
    Use of uninitialized value in length at scripts/checkpatch.pl line 1480.
    Use of uninitialized value in substr at scripts/checkpatch.pl line 1480.
    Use of uninitialized value in substr at scripts/checkpatch.pl line 1480.
    Use of uninitialized value in pattern match (m//) at scripts/checkpatch.pl line 1488.
    Use of uninitialized value in pattern match (m//) at scripts/checkpatch.pl line 1545.
    total: 0 errors, 0 warnings, 72 lines checked




    From: Wu Fengguang <fengguang.wu@intel.com>

    For mem_cgroup, shrink_zone() may call shrink_list() with nr_to_scan=1, in
    which case shrink_list() _still_ calls isolate_pages() with the much
    larger SWAP_CLUSTER_MAX. It effectively scales up the inactive list scan
    rate by up to 32 times.

    For example, with 16k inactive pages and DEF_PRIORITY=12, (16k >> 12)=4.
    So when shrink_zone() expects to scan 4 pages in the active/inactive list,
    the active list will be scanned 4 pages, while the inactive list will be
    (over) scanned SWAP_CLUSTER_MAX=32 pages in effect. And that could break
    the balance between the two lists.

    It can further impact the scan of anon active list, due to the anon
    active/inactive ratio rebalance logic in balance_pgdat()/shrink_zone():

    inactive anon list over scanned => inactive_anon_is_low() == TRUE
    => shrink_active_list()
    => active anon list over scanned

    So the end result may be

    - anon inactive => over scanned
    - anon active => over scanned (maybe not as much)
    - file inactive => over scanned
    - file active => under scanned (relatively)

    The accesses to nr_saved_scan are not lock protected and so not 100%
    accurate, however we can tolerate small errors and the resulted small
    imbalanced scan rates between zones.

    Cc: Rik van Riel <riel@redhat.com>
    Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
    Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com>
    Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
    Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    ---

    include/linux/mmzone.h | 6 +++++-
    mm/page_alloc.c | 2 +-
    mm/vmscan.c | 20 +++++++++++---------
    3 files changed, 17 insertions(+), 11 deletions(-)

    diff -puN include/linux/mmzone.h~mm-do-batched-scans-for-mem_cgroup include/linux/mmzone.h
    --- a/include/linux/mmzone.h~mm-do-batched-scans-for-mem_cgroup
    +++ a/include/linux/mmzone.h
    @@ -273,6 +273,11 @@ struct zone_reclaim_stat {
    */
    unsigned long recent_rotated[2];
    unsigned long recent_scanned[2];
    +
    + /*
    + * accumulated for batching
    + */
    + unsigned long nr_saved_scan[NR_LRU_LISTS];
    };

    struct zone {
    @@ -327,7 +332,6 @@ struct zone {
    spinlock_t lru_lock;
    struct zone_lru {
    struct list_head list;
    - unsigned long nr_saved_scan; /* accumulated for batching */
    } lru[NR_LRU_LISTS];

    struct zone_reclaim_stat reclaim_stat;
    diff -puN mm/page_alloc.c~mm-do-batched-scans-for-mem_cgroup mm/page_alloc.c
    --- a/mm/page_alloc.c~mm-do-batched-scans-for-mem_cgroup
    +++ a/mm/page_alloc.c
    @@ -3830,7 +3830,7 @@ static void __paginginit free_area_init_
    zone_pcp_init(zone);
    for_each_lru(l) {
    INIT_LIST_HEAD(&zone->lru[l].list);
    - zone->lru[l].nr_saved_scan = 0;
    + zone->reclaim_stat.nr_saved_scan[l] = 0;
    }
    zone->reclaim_stat.recent_rotated[0] = 0;
    zone->reclaim_stat.recent_rotated[1] = 0;
    diff -puN mm/vmscan.c~mm-do-batched-scans-for-mem_cgroup mm/vmscan.c
    --- a/mm/vmscan.c~mm-do-batched-scans-for-mem_cgroup
    +++ a/mm/vmscan.c
    @@ -1586,6 +1586,7 @@ static void shrink_zone(int priority, st
    enum lru_list l;
    unsigned long nr_reclaimed = sc->nr_reclaimed;
    unsigned long swap_cluster_max = sc->swap_cluster_max;
    + struct zone_reclaim_stat *reclaim_stat = get_reclaim_stat(zone, sc);
    int noswap = 0;

    /* If we have no swap space, do not bother scanning anon pages. */
    @@ -1605,12 +1606,9 @@ static void shrink_zone(int priority, st
    scan >>= priority;
    scan = (scan * percent[file]) / 100;
    }
    - if (scanning_global_lru(sc))
    - nr[l] = nr_scan_try_batch(scan,
    - &zone->lru[l].nr_saved_scan,
    - swap_cluster_max);
    - else
    - nr[l] = scan;
    + nr[l] = nr_scan_try_batch(scan,
    + &reclaim_stat->nr_saved_scan[l],
    + swap_cluster_max);
    }

    while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] ||
    @@ -2220,6 +2218,7 @@ static void shrink_all_zones(unsigned lo
    {
    struct zone *zone;
    unsigned long nr_reclaimed = 0;
    + struct zone_reclaim_stat *reclaim_stat;

    for_each_populated_zone(zone) {
    enum lru_list l;
    @@ -2236,11 +2235,14 @@ static void shrink_all_zones(unsigned lo
    l == LRU_ACTIVE_FILE))
    continue;

    - zone->lru[l].nr_saved_scan += (lru_pages >> prio) + 1;
    - if (zone->lru[l].nr_saved_scan >= nr_pages || pass > 3) {
    + reclaim_stat = get_reclaim_stat(zone, sc);
    + reclaim_stat->nr_saved_scan[l] +=
    + (lru_pages >> prio) + 1;
    + if (reclaim_stat->nr_saved_scan[l]
    + >= nr_pages || pass > 3) {
    unsigned long nr_to_scan;

    - zone->lru[l].nr_saved_scan = 0;
    + reclaim_stat->nr_saved_scan[l] = 0;
    nr_to_scan = min(nr_pages, lru_pages);
    nr_reclaimed += shrink_list(l, nr_to_scan, zone,
    sc, prio);
    _


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