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authorKOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>2010-08-09 17:19:27 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2010-08-09 20:45:00 -0700
commit25edde0332916ae706ccf83de688be57bcc844b7 (patch)
tree35a5b0e651f9cdb48d9a55a748970339c4f681bc /mm/memcontrol.c
parentb898cc70019ce1835bbf6c47bdf978adc36faa42 (diff)
downloadvexpress-lsk-25edde0332916ae706ccf83de688be57bcc844b7.tar.gz
vmscan: kill prev_priority completely
Since 2.6.28 zone->prev_priority is unused. Then it can be removed safely. It reduce stack usage slightly. Now I have to say that I'm sorry. 2 years ago, I thought prev_priority can be integrate again, it's useful. but four (or more) times trying haven't got good performance number. Thus I give up such approach. The rest of this changelog is notes on prev_priority and why it existed in the first place and why it might be not necessary any more. This information is based heavily on discussions between Andrew Morton, Rik van Riel and Kosaki Motohiro who is heavily quotes from. Historically prev_priority was important because it determined when the VM would start unmapping PTE pages. i.e. there are no balances of note within the VM, Anon vs File and Mapped vs Unmapped. Without prev_priority, there is a potential risk of unnecessarily increasing minor faults as a large amount of read activity of use-once pages could push mapped pages to the end of the LRU and get unmapped. There is no proof this is still a problem but currently it is not considered to be. Active files are not deactivated if the active file list is smaller than the inactive list reducing the liklihood that file-mapped pages are being pushed off the LRU and referenced executable pages are kept on the active list to avoid them getting pushed out by read activity. Even if it is a problem, prev_priority prev_priority wouldn't works nowadays. First of all, current vmscan still a lot of UP centric code. it expose some weakness on some dozens CPUs machine. I think we need more and more improvement. The problem is, current vmscan mix up per-system-pressure, per-zone-pressure and per-task-pressure a bit. example, prev_priority try to boost priority to other concurrent priority. but if the another task have mempolicy restriction, it is unnecessary, but also makes wrong big latency and exceeding reclaim. per-task based priority + prev_priority adjustment make the emulation of per-system pressure. but it have two issue 1) too rough and brutal emulation 2) we need per-zone pressure, not per-system. Another example, currently DEF_PRIORITY is 12. it mean the lru rotate about 2 cycle (1/4096 + 1/2048 + 1/1024 + .. + 1) before invoking OOM-Killer. but if 10,0000 thrreads enter DEF_PRIORITY reclaim at the same time, the system have higher memory pressure than priority==0 (1/4096*10,000 > 2). prev_priority can't solve such multithreads workload issue. In other word, prev_priority concept assume the sysmtem don't have lots threads." Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Signed-off-by: Mel Gorman <mel@csn.ul.ie> Reviewed-by: Johannes Weiner <hannes@cmpxchg.org> Reviewed-by: Rik van Riel <riel@redhat.com> Cc: Dave Chinner <david@fromorbit.com> Cc: Chris Mason <chris.mason@oracle.com> Cc: Nick Piggin <npiggin@suse.de> Cc: Rik van Riel <riel@redhat.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Christoph Hellwig <hch@infradead.org> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Michael Rubin <mrubin@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/memcontrol.c')
-rw-r--r--mm/memcontrol.c31
1 files changed, 0 insertions, 31 deletions
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 20a8193a7af..31abd1c2c0c 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -211,8 +211,6 @@ struct mem_cgroup {
*/
spinlock_t reclaim_param_lock;
- int prev_priority; /* for recording reclaim priority */
-
/*
* While reclaiming in a hierarchy, we cache the last child we
* reclaimed from.
@@ -858,35 +856,6 @@ int task_in_mem_cgroup(struct task_struct *task, const struct mem_cgroup *mem)
return ret;
}
-/*
- * prev_priority control...this will be used in memory reclaim path.
- */
-int mem_cgroup_get_reclaim_priority(struct mem_cgroup *mem)
-{
- int prev_priority;
-
- spin_lock(&mem->reclaim_param_lock);
- prev_priority = mem->prev_priority;
- spin_unlock(&mem->reclaim_param_lock);
-
- return prev_priority;
-}
-
-void mem_cgroup_note_reclaim_priority(struct mem_cgroup *mem, int priority)
-{
- spin_lock(&mem->reclaim_param_lock);
- if (priority < mem->prev_priority)
- mem->prev_priority = priority;
- spin_unlock(&mem->reclaim_param_lock);
-}
-
-void mem_cgroup_record_reclaim_priority(struct mem_cgroup *mem, int priority)
-{
- spin_lock(&mem->reclaim_param_lock);
- mem->prev_priority = priority;
- spin_unlock(&mem->reclaim_param_lock);
-}
-
static int calc_inactive_ratio(struct mem_cgroup *memcg, unsigned long *present_pages)
{
unsigned long active;