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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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