On Tue, Apr 26, 2011 at 2:17 AM, KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote:
At memory reclaim, we determine the number of pages to be scanned
per zone as
(anon + file) >> priority.
Assume
scan = (anon + file) >> priority.
If scan < SWAP_CLUSTER_MAX, shlink_list will be skipped for this
priority and results no-sacn. This has some problems.
1. This increases priority as 1 without any scan.
To do scan in DEF_PRIORITY always, amount of pages should be larger than
512M. If pages>>priority < SWAP_CLUSTER_MAX, it's recorded and scan will be
batched, later. (But we lose 1 priority.)
But if the amount of pages is smaller than 16M, no scan at priority==0
forever.
2. If zone->all_unreclaimabe==true, it's scanned only when priority==0.
So, x86's ZONE_DMA will never be recoverred until the user of pages
frees memory by itself.
3. With memcg, the limit of memory can be small. When using small memcg,
it gets priority < DEF_PRIORITY-2 very easily and need to call
wait_iff_congested().
For doing scan before priorty=9, 64MB of memory should be used.
This patch tries to scan SWAP_CLUSTER_MAX of pages in force...when
1. the target is enough small.
2. it's kswapd or memcg reclaim.
Then we can avoid rapid priority drop and may be able to recover
all_unreclaimable in a small zones.
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
---
mm/vmscan.c | 31 ++++++++++++++++++++++++++-----
1 file changed, 26 insertions(+), 5 deletions(-)
Index: memcg/mm/vmscan.c
===================================================================
--- memcg.orig/mm/vmscan.c
+++ memcg/mm/vmscan.c
@@ -1737,6 +1737,16 @@ static void get_scan_count(struct zone *
u64 fraction[2], denominator;
enum lru_list l;
int noswap = 0;
+ int may_noscan = 0;
+
+
extra line?
+ anon = zone_nr_lru_pages(zone, sc, LRU_ACTIVE_ANON) +
+ zone_nr_lru_pages(zone, sc, LRU_INACTIVE_ANON);
+ file = zone_nr_lru_pages(zone, sc, LRU_ACTIVE_FILE) +
+ zone_nr_lru_pages(zone, sc, LRU_INACTIVE_FILE);
+
+ if (((anon + file) >> priority) < SWAP_CLUSTER_MAX)
+ may_noscan = 1;
/* If we have no swap space, do not bother scanning anon pages. */
if (!sc->may_swap || (nr_swap_pages <= 0)) {
@@ -1747,11 +1757,6 @@ static void get_scan_count(struct zone *
goto out;
}
- anon = zone_nr_lru_pages(zone, sc, LRU_ACTIVE_ANON) +
- zone_nr_lru_pages(zone, sc, LRU_INACTIVE_ANON);
- file = zone_nr_lru_pages(zone, sc, LRU_ACTIVE_FILE) +
- zone_nr_lru_pages(zone, sc, LRU_INACTIVE_FILE);
-
if (scanning_global_lru(sc)) {
free = zone_page_state(zone, NR_FREE_PAGES);
/* If we have very few page cache pages,
@@ -1814,10 +1819,26 @@ out:
unsigned long scan;
scan = zone_nr_lru_pages(zone, sc, l);
+
extra line?
if (priority || noswap) {
scan >>= priority;
scan = div64_u64(scan * fraction[file], denominator);
}
+
+ if (!scan &&
+ may_noscan &&
+ (current_is_kswapd() || !scanning_global_lru(sc))) {
+ /*
+ * if we do target scan, the whole amount of memory
+ * can be too small to scan with low priority value.
+ * This raise up priority rapidly without any scan.
+ * Avoid that and give some scan.
+ */
+ if (file)
+ scan = SWAP_CLUSTER_MAX;
+ else if (!noswap && (fraction[anon] > fraction[file]*16))
+ scan = SWAP_CLUSTER_MAX;
+ }
Ok, so we are changing the global kswapd, and per-memcg bg and direct reclaim both. Just to be clear here.
Also, how did we calculated the "16" to be the fraction of anon vs file?
nr[l] = nr_scan_try_batch(scan,
&reclaim_stat->nr_saved_scan[l]);
}
Thank you
--Ying