[RFC][PATCH] mm: merge as soon as possible when pcp alloc/free

From: Xishi Qiu
Date: Sat Nov 05 2016 - 04:06:05 EST

Usually the memory of android phones is very small, so after a long
running, the fragment is very large. Kernel stack which called by
alloc_thread_stack_node() usually alloc 16K memory, and it failed
frequently.

However we have CONFIG_VMAP_STACK now, but it do not support arm64,
and maybe it has some regression because of vmalloc, it need to
find an area and create page table dynamically, this will take a short
time.

I think we can merge as soon as possible when pcp alloc/free to reduce
fragment. The pcp page is hot page, so free it will cause cache miss,
I use perf to test it, but it seems the regression is not so much, maybe
it need to test more. Any reply is welcome.

no patch:
perf stat -e cache-misses make -j50

Kernel: arch/x86/boot/bzImage is ready (#10)

Performance counter stats for 'make -j50':

17,845,292,704 cache-misses

157.605906725 seconds time elapsed

patched:
perf stat -e cache-misses make -j50

Kernel: arch/x86/boot/bzImage is ready (#8)

Performance counter stats for 'make -j50':

17,876,726,774 cache-misses

156.293720662 seconds time elapsed

nopatch:
make clean, dropcache, then make -j50, CONFIG_VMAP_STACK is off
[root@localhost ~]# cat /proc/buddyinfo
Node 0, zone DMA 3 0 2 1 3 2 2 1 0 1 3
Node 0, zone DMA32 4 4 1 5 2 4 2 2 3 1 447
Node 0, zone Normal 2389 418 668 707 738 451 246 93 42 21 15147
Node 1, zone Normal 1137 386 583 631 878 311 80 12 2 8 15640
Node 2, zone Normal 1875 230 323 462 729 453 177 67 12 9 15749
Node 3, zone Normal 1675 452 503 898 928 628 256 70 25 14 11688
Node 4, zone Normal 1917 407 306 2706 1722 909 477 218 54 34 15682
Node 5, zone Normal 4330 9785 6265 2612 1404 703 276 113 33 7 15730
Node 6, zone Normal 754 211 1093 1023 748 599 352 193 107 43 15672
Node 7, zone Normal 1092 133 819 807 729 549 254 120 52 28 15500
[root@localhost ~]# cat /sys/kernel/debug/extfrag/unusable_index
Node 0, zone DMA 0.000 0.000 0.000 0.002 0.004 0.016 0.032 0.065 0.097 0.097 0.226
Node 0, zone DMA32 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.001 0.002 0.004
Node 0, zone Normal 0.000 0.000 0.000 0.000 0.000 0.001 0.002 0.003 0.004 0.004 0.005
Node 1, zone Normal 0.000 0.000 0.000 0.000 0.000 0.001 0.002 0.002 0.002 0.002 0.002
Node 2, zone Normal 0.000 0.000 0.000 0.000 0.000 0.001 0.002 0.002 0.003 0.003 0.003
Node 3, zone Normal 0.000 0.000 0.000 0.000 0.000 0.002 0.003 0.005 0.005 0.006 0.007
Node 4, zone Normal 0.000 0.000 0.000 0.000 0.001 0.003 0.005 0.006 0.008 0.009 0.010
Node 5, zone Normal 0.000 0.000 0.001 0.003 0.004 0.005 0.007 0.008 0.009 0.009 0.009
Node 6, zone Normal 0.000 0.000 0.000 0.000 0.000 0.001 0.002 0.004 0.005 0.007 0.008
Node 7, zone Normal 0.000 0.000 0.000 0.000 0.000 0.001 0.002 0.003 0.004 0.005 0.006

patched:
make clean, dropcache, then make -j50, CONFIG_VMAP_STACK is off
[root@localhost ~]# cat /proc/buddyinfo
Node 0, zone DMA 1 1 2 1 3 2 2 1 0 1 3
Node 0, zone DMA32 3 3 0 2 2 4 2 2 3 1 447
Node 0, zone Normal 1293 1097 159 564 620 392 242 89 49 21 15154
Node 1, zone Normal 1195 369 155 73 295 260 92 32 8 10 15769
Node 2, zone Normal 1478 434 160 846 1397 590 274 118 39 25 15753
Node 3, zone Normal 892 285 176 625 691 450 226 78 33 14 11596
Node 4, zone Normal 604 217 28 468 1560 690 292 126 46 31 15741
Node 5, zone Normal 888 225 101 263 483 319 196 97 30 24 15726
Node 6, zone Normal 1908 9294 7075 3373 1765 759 243 128 21 20 15591
Node 7, zone Normal 1362 1126 1271 646 558 377 170 84 37 35 15602
[root@localhost ~]# cat /sys/kernel/debug/extfrag/unusable_index
Node 0, zone DMA 0.000 0.000 0.000 0.002 0.004 0.016 0.032 0.065 0.097 0.097 0.226
Node 0, zone DMA32 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.001 0.002 0.004
Node 0, zone Normal 0.000 0.000 0.000 0.000 0.000 0.001 0.001 0.002 0.003 0.004 0.005
Node 1, zone Normal 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.001 0.001 0.001 0.001
Node 2, zone Normal 0.000 0.000 0.000 0.000 0.000 0.002 0.003 0.004 0.005 0.005 0.006
Node 3, zone Normal 0.000 0.000 0.000 0.000 0.000 0.001 0.002 0.003 0.004 0.005 0.005
Node 4, zone Normal 0.000 0.000 0.000 0.000 0.000 0.001 0.003 0.004 0.005 0.006 0.007
Node 5, zone Normal 0.000 0.000 0.000 0.000 0.000 0.000 0.001 0.002 0.002 0.003 0.004
Node 6, zone Normal 0.000 0.000 0.001 0.003 0.004 0.006 0.007 0.008 0.009 0.010 0.010
Node 7, zone Normal 0.000 0.000 0.000 0.000 0.000 0.001 0.002 0.002 0.003 0.004 0.005


Signed-off-by: Xishi Qiu <qiuxishi@xxxxxxxxxx>
---
mm/page_alloc.c | 29 +++++++++++++++++++++++++++++
1 file changed, 29 insertions(+)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 8fd42aa..82257e6 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2413,6 +2413,8 @@ void free_hot_cold_page(struct page *page, bool cold)
unsigned long flags;
unsigned long pfn = page_to_pfn(page);
int migratetype;
+ unsigned long page_idx = pfn & 1UL;
+ struct page *buddy;

if (!free_pcp_prepare(page))
return;
@@ -2437,6 +2439,16 @@ void free_hot_cold_page(struct page *page, bool cold)
migratetype = MIGRATE_MOVABLE;
}

+ if (page_idx)
+ buddy = page - 1;
+ else
+ buddy = page + 1;
+ /* merge immediately if buddy is free */
+ if (PageBuddy(buddy)) {
+ free_one_page(zone, page, pfn, 0, migratetype);
+ goto out;
+ }
+
pcp = &this_cpu_ptr(zone->pageset)->pcp;
if (!cold)
list_add(&page->lru, &pcp->lists[migratetype]);
@@ -2591,8 +2603,12 @@ struct page *buffered_rmqueue(struct zone *preferred_zone,
if (likely(order == 0)) {
struct per_cpu_pages *pcp;
struct list_head *list;
+ unsigned long page_idx;
+ struct page *buddy;
+ int retry = 0;

local_irq_save(flags);
+retry:
do {
pcp = &this_cpu_ptr(zone->pageset)->pcp;
list = &pcp->lists[migratetype];
@@ -2612,6 +2628,19 @@ struct page *buffered_rmqueue(struct zone *preferred_zone,
list_del(&page->lru);
pcp->count--;

+ page_idx = page_to_pfn(page) & 1UL;
+ if (page_idx)
+ buddy = page - 1;
+ else
+ buddy = page + 1;
+ /* merge immediately if buddy is free */
+ if (PageBuddy(buddy) && retry < 3) {
+ free_one_page(page_zone(page), page,
+ page_to_pfn(page), 0, migratetype);
+ retry++;
+ goto retry;
+ }
+
} while (check_new_pcp(page));
} else {
/*
--
1.8.3.1