On Fri, Apr 29, 2011 at 10:28:24AM +0800, Wu Fengguang wrote:
> > Test results:
> >
> > - the failure rate is pretty sensible to the page reclaim size,
> > from 282 (WMARK_HIGH) to 704 (WMARK_MIN) to 10496 (SWAP_CLUSTER_MAX)
> >
> > - the IPIs are reduced by over 100 times
>
> It's reduced by 500 times indeed.
>
> CAL: 220449 220246 220372 220558 220251 219740 220043 219968 Function call interrupts
> CAL: 93 463 410 540 298 282 272 306 Function call interrupts
>
> > base kernel: vanilla 2.6.39-rc3 + __GFP_NORETRY readahead page allocation patch
> > -------------------------------------------------------------------------------
> > nr_alloc_fail 10496
> > allocstall 1576602
>
> > patched (WMARK_MIN)
> > -------------------
> > nr_alloc_fail 704
> > allocstall 105551
>
> > patched (WMARK_HIGH)
> > --------------------
> > nr_alloc_fail 282
> > allocstall 53860
>
> > this patch (WMARK_HIGH, limited scan)
> > -------------------------------------
> > nr_alloc_fail 276
> > allocstall 54034
>
> There is a bad side effect though: the much reduced "allocstall" means
> each direct reclaim will take much more time to complete. A simple solution
> is to terminate direct reclaim after 10ms. I noticed that an 100ms
> time threshold can reduce the reclaim latency from 621ms to 358ms.
> Further lowering the time threshold to 20ms does not help reducing the
> real latencies though.
Experiments going on...
I tried the more reasonable terminate condition: stop direct reclaim
when the preferred zone is above high watermark (see the below chunk).
This helps reduce the average reclaim latency to under 100ms in the
1000-dd case.
However nr_alloc_fail is around 5000 and not ideal. The interesting
thing is, even if zone watermark is high, the task still may fail to
get a free page..
@@ -2067,8 +2072,17 @@ static unsigned long do_try_to_free_page
}
}
total_scanned += sc->nr_scanned;
- if (sc->nr_reclaimed >= sc->nr_to_reclaim)
- goto out;
+ if (sc->nr_reclaimed >= min_reclaim) {
+ if (sc->nr_reclaimed >= sc->nr_to_reclaim)
+ goto out;
+ if (total_scanned > 2 * sc->nr_to_reclaim)
+ goto out;
+ if (preferred_zone &&
+ zone_watermark_ok_safe(preferred_zone, sc->order,
+ high_wmark_pages(preferred_zone),
+ zone_idx(preferred_zone), 0))
+ goto out;
+ }
/*
* Try to write back as many pages as we just scanned. This
Thanks,
Fengguang
---
Subject: mm: cut down __GFP_NORETRY page allocation failures
Date: Thu Apr 28 13:46:39 CST 2011
Concurrent page allocations are suffering from high failure rates.
On a 8p, 3GB ram test box, when reading 1000 sparse files of size 1GB,
the page allocation failures are
nr_alloc_fail 733 # interleaved reads by 1 single task
nr_alloc_fail 11799 # concurrent reads by 1000 tasks
The concurrent read test script is:
for i in `seq 1000`
do
truncate -s 1G /fs/sparse-$i
dd if=/fs/sparse-$i of=/dev/null &
done
In order for get_page_from_freelist() to get free page,
(1) try_to_free_pages() should use much higher .nr_to_reclaim than the
current SWAP_CLUSTER_MAX=32, in order to draw the zone out of the
possible low watermark state as well as fill the pcp with enough free
pages to overflow its high watermark.
(2) the get_page_from_freelist() _after_ direct reclaim should use lower
watermark than its normal invocations, so that it can reasonably
"reserve" some free pages for itself and prevent other concurrent
page allocators stealing all its reclaimed pages.
Some notes:
- commit 9ee493ce ("mm: page allocator: drain per-cpu lists after direct
reclaim allocation fails") has the same target, however is obviously
costly and less effective. It seems more clean to just remove the
retry and drain code than to retain it.
- it's a bit hacky to reclaim more than requested pages inside
do_try_to_free_page(), and it won't help cgroup for now
- it only aims to reduce failures when there are plenty of reclaimable
pages, so it stops the opportunistic reclaim when scanned 2 times pages
Test results:
- the failure rate is pretty sensible to the page reclaim size,
from 282 (WMARK_HIGH) to 704 (WMARK_MIN) to 10496 (SWAP_CLUSTER_MAX)
- the IPIs are reduced by over 100 times
base kernel: vanilla 2.6.39-rc3 + __GFP_NORETRY readahead page allocation patch
-------------------------------------------------------------------------------
nr_alloc_fail 10496
allocstall 1576602
slabs_scanned 21632
kswapd_steal 4393382
kswapd_inodesteal 124
kswapd_low_wmark_hit_quickly 885
kswapd_high_wmark_hit_quickly 2321
kswapd_skip_congestion_wait 0
pageoutrun 29426
CAL: 220449 220246 220372 220558 220251 219740 220043 219968 Function call interrupts
LOC: 536274 532529 531734 536801 536510 533676 534853 532038 Local timer interrupts
RES: 3032 2128 1792 1765 2184 1703 1754 1865 Rescheduling interrupts
TLB: 189 15 13 17 64 294 97 63 TLB shootdowns
patched (WMARK_MIN)
-------------------
nr_alloc_fail 704
allocstall 105551
slabs_scanned 33280
kswapd_steal 4525537
kswapd_inodesteal 187
kswapd_low_wmark_hit_quickly 4980
kswapd_high_wmark_hit_quickly 2573
kswapd_skip_congestion_wait 0
pageoutrun 35429
CAL: 93 286 396 754 272 297 275 281 Function call interrupts
LOC: 520550 517751 517043 522016 520302 518479 519329 517179 Local timer interrupts
RES: 2131 1371 1376 1269 1390 1181 1409 1280 Rescheduling interrupts
TLB: 280 26 27 30 65 305 134 75 TLB shootdowns
patched (WMARK_HIGH)
--------------------
nr_alloc_fail 282
allocstall 53860
slabs_scanned 23936
kswapd_steal 4561178
kswapd_inodesteal 0
kswapd_low_wmark_hit_quickly 2760
kswapd_high_wmark_hit_quickly 1748
kswapd_skip_congestion_wait 0
pageoutrun 32639
CAL: 93 463 410 540 298 282 272 306 Function call interrupts
LOC: 513956 510749 509890 514897 514300 512392 512825 510574 Local timer interrupts
RES: 1174 2081 1411 1320 1742 2683 1380 1230 Rescheduling interrupts
TLB: 274 21 19 22 57 317 131 61 TLB shootdowns
patched (WMARK_HIGH, limited scan)
----------------------------------
nr_alloc_fail 276
allocstall 54034
slabs_scanned 24320
kswapd_steal 4507482
kswapd_inodesteal 262
kswapd_low_wmark_hit_quickly 2638
kswapd_high_wmark_hit_quickly 1710
kswapd_skip_congestion_wait 0
pageoutrun 32182
CAL: 69 443 421 567 273 279 269 334 Function call interrupts
LOC: 514736 511698 510993 514069 514185 512986 513838 511229 Local timer interrupts
RES: 2153 1556 1126 1351 3047 1554 1131 1560 Rescheduling interrupts
TLB: 209 26 20 15 71 315 117 71 TLB shootdowns
patched (WMARK_HIGH, limited scan, stop on watermark OK), 100 dd
----------------------------------------------------------------
start time: 3
total time: 50
nr_alloc_fail 162
allocstall 45523
CPU count real total virtual total delay total
921 3024540200 3009244668 37123129525
IO count delay total delay average
0 0 0ms
SWAP count delay total delay average
0 0 0ms
RECLAIM count delay total delay average
357 4891766796 13ms
dd: read=0, write=0, cancelled_write=0
patched (WMARK_HIGH, limited scan, stop on watermark OK), 1000 dd
-----------------------------------------------------------------
start time: 272
total time: 509
nr_alloc_fail 3913
allocstall 541789
CPU count real total virtual total delay total
1044 3445476208 3437200482 229919915202
IO count delay total delay average
0 0 0ms
SWAP count delay total delay average
0 0 0ms
RECLAIM count delay total delay average
452 34691441605 76ms
dd: read=0, write=0, cancelled_write=0
patched (WMARK_HIGH, limited scan, stop on watermark OK, no time limit), 1000 dd
--------------------------------------------------------------------------------
start time: 278
total time: 513
nr_alloc_fail 4737
allocstall 436392
CPU count real total virtual total delay total
1024 3371487456 3359441487 225088210977
IO count delay total delay average
1 160631171 160ms
SWAP count delay total delay average
0 0 0ms
RECLAIM count delay total delay average
367 30809994722 83ms
dd: read=20480, write=0, cancelled_write=0
no cond_resched():
start time: 263
total time: 516
nr_alloc_fail 5144
allocstall 436787
CPU count real total virtual total delay total
1018 3305497488 3283831119 241982934044
IO count delay total delay average
0 0 0ms
SWAP count delay total delay average
0 0 0ms
RECLAIM count delay total delay average
328 31398481378 95ms
dd: read=0, write=0, cancelled_write=0
zone_watermark_ok_safe():
start time: 266
total time: 513
nr_alloc_fail 4526
allocstall 440246
CPU count real total virtual total delay total
1119 3640446568 3619184439 240945024724
IO count delay total delay average
3 303620082 101ms
SWAP count delay total delay average
0 0 0ms
RECLAIM count delay total delay average
372 27320731898 73ms
dd: read=77824, write=0, cancelled_write=0
start time: 275
total time: 517
nr_alloc_fail 4694
allocstall 431021
CPU count real total virtual total delay total
1073 3534462680 3512544928 234056498221
IO count delay total delay average
0 0 0ms
SWAP count delay total delay average
0 0 0ms
RECLAIM count delay total delay average
386 34751778363 89ms
dd: read=0, write=0, cancelled_write=0
CC: Mel Gorman <mel@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
---
fs/buffer.c | 4 ++--
include/linux/swap.h | 3 ++-
mm/page_alloc.c | 20 +++++---------------
mm/vmscan.c | 31 +++++++++++++++++++++++--------
4 files changed, 32 insertions(+), 26 deletions(-)
--- linux-next.orig/mm/vmscan.c 2011-04-29 10:42:14.000000000 +0800
+++ linux-next/mm/vmscan.c 2011-04-30 21:59:33.000000000 +0800
@@ -2025,8 +2025,9 @@ static bool all_unreclaimable(struct zon
* returns: 0, if no pages reclaimed
* else, the number of pages reclaimed
*/
-static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
- struct scan_control *sc)
+static unsigned long do_try_to_free_pages(struct zone *preferred_zone,
+ struct zonelist *zonelist,
+ struct scan_control *sc)
{
int priority;
unsigned long total_scanned = 0;
@@ -2034,6 +2035,7 @@ static unsigned long do_try_to_free_page
struct zoneref *z;
struct zone *zone;
unsigned long writeback_threshold;
+ unsigned long min_reclaim = sc->nr_to_reclaim;
get_mems_allowed();
delayacct_freepages_start();
@@ -2041,6 +2043,9 @@ static unsigned long do_try_to_free_page
if (scanning_global_lru(sc))
count_vm_event(ALLOCSTALL);
+ if (preferred_zone)
+ sc->nr_to_reclaim += preferred_zone->watermark[WMARK_HIGH];
+
for (priority = DEF_PRIORITY; priority >= 0; priority--) {
sc->nr_scanned = 0;
if (!priority)
@@ -2067,8 +2072,17 @@ static unsigned long do_try_to_free_page
}
}
total_scanned += sc->nr_scanned;
- if (sc->nr_reclaimed >= sc->nr_to_reclaim)
- goto out;
+ if (sc->nr_reclaimed >= min_reclaim) {
+ if (sc->nr_reclaimed >= sc->nr_to_reclaim)
+ goto out;
+ if (total_scanned > 2 * sc->nr_to_reclaim)
+ goto out;
+ if (preferred_zone &&
+ zone_watermark_ok_safe(preferred_zone, sc->order,
+ high_wmark_pages(preferred_zone),
+ zone_idx(preferred_zone), 0))
+ goto out;
+ }
/*
* Try to write back as many pages as we just scanned. This
@@ -2117,7 +2131,8 @@ out:
return 0;
}
-unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
+unsigned long try_to_free_pages(struct zone *preferred_zone,
+ struct zonelist *zonelist, int order,
gfp_t gfp_mask, nodemask_t *nodemask)
{
unsigned long nr_reclaimed;
@@ -2137,7 +2152,7 @@ unsigned long try_to_free_pages(struct z
sc.may_writepage,
gfp_mask);
- nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
+ nr_reclaimed = do_try_to_free_pages(preferred_zone, zonelist, &sc);
trace_mm_vmscan_direct_reclaim_end(nr_reclaimed);
@@ -2207,7 +2222,7 @@ unsigned long try_to_free_mem_cgroup_pag
sc.may_writepage,
sc.gfp_mask);
- nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
+ nr_reclaimed = do_try_to_free_pages(NULL, zonelist, &sc);
trace_mm_vmscan_memcg_reclaim_end(nr_reclaimed);
@@ -2796,7 +2811,7 @@ unsigned long shrink_all_memory(unsigned
reclaim_state.reclaimed_slab = 0;
p->reclaim_state = &reclaim_state;
- nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
+ nr_reclaimed = do_try_to_free_pages(NULL, zonelist, &sc);
p->reclaim_state = NULL;
lockdep_clear_current_reclaim_state();
--- linux-next.orig/mm/page_alloc.c 2011-04-29 10:42:15.000000000 +0800
+++ linux-next/mm/page_alloc.c 2011-04-30 21:29:40.000000000 +0800
@@ -1888,9 +1888,8 @@ __alloc_pages_direct_reclaim(gfp_t gfp_m
nodemask_t *nodemask, int alloc_flags, struct zone *preferred_zone,
int migratetype, unsigned long *did_some_progress)
{
- struct page *page = NULL;
+ struct page *page;
struct reclaim_state reclaim_state;
- bool drained = false;
cond_resched();
@@ -1901,7 +1900,8 @@ __alloc_pages_direct_reclaim(gfp_t gfp_m
reclaim_state.reclaimed_slab = 0;
current->reclaim_state = &reclaim_state;
- *did_some_progress = try_to_free_pages(zonelist, order, gfp_mask, nodemask);
+ *did_some_progress = try_to_free_pages(preferred_zone, zonelist, order,
+ gfp_mask, nodemask);
current->reclaim_state = NULL;
lockdep_clear_current_reclaim_state();
@@ -1912,22 +1912,12 @@ __alloc_pages_direct_reclaim(gfp_t gfp_m
if (unlikely(!(*did_some_progress)))
return NULL;
-retry:
+ alloc_flags |= ALLOC_HARDER;
+
page = get_page_from_freelist(gfp_mask, nodemask, order,
zonelist, high_zoneidx,
alloc_flags, preferred_zone,
migratetype);
-
- /*
- * If an allocation failed after direct reclaim, it could be because
- * pages are pinned on the per-cpu lists. Drain them and try again
- */
- if (!page && !drained) {
- drain_all_pages();
- drained = true;
- goto retry;
- }
-
return page;
}
--- linux-next.orig/fs/buffer.c 2011-04-30 13:26:57.000000000 +0800
+++ linux-next/fs/buffer.c 2011-04-30 13:29:08.000000000 +0800
@@ -288,8 +288,8 @@ static void free_more_memory(void)
gfp_zone(GFP_NOFS), NULL,
&zone);
if (zone)
- try_to_free_pages(node_zonelist(nid, GFP_NOFS), 0,
- GFP_NOFS, NULL);
+ try_to_free_pages(zone, node_zonelist(nid, GFP_NOFS),
+ 0, GFP_NOFS, NULL);
}
}
--- linux-next.orig/include/linux/swap.h 2011-04-30 13:30:36.000000000 +0800
+++ linux-next/include/linux/swap.h 2011-04-30 13:31:03.000000000 +0800
@@ -249,7 +249,8 @@ static inline void lru_cache_add_file(st
#define ISOLATE_BOTH 2 /* Isolate both active and inactive pages. */
/* linux/mm/vmscan.c */
-extern unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
+extern unsigned long try_to_free_pages(struct zone *preferred_zone,
+ struct zonelist *zonelist, int order,
gfp_t gfp_mask, nodemask_t *mask);
extern unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *mem,
gfp_t gfp_mask, bool noswap,
--
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