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Date: Tue, 22 Nov 2011 19:32:40 -0800 (PST)
From: David Rientjes <rientjes@...gle.com>
To: Miao Xie <miaox@...fujitsu.com>
cc: Andrew Morton <akpm@...ux-foundation.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
Paul Menage <paul@...lmenage.org>,
linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [patch for-3.2-rc3] cpusets: stall when updating mems_allowed
for mempolicy or disjoint nodemask
On Wed, 23 Nov 2011, Miao Xie wrote:
> Yes, what you said is right.
> But in fact, on the kernel where MAX_NUMNODES <= BITS_PER_LONG, the same problem
> can also occur.
> task1 task1's mems task2
> alloc page 2-3
> alloc on node1? NO 2-3
> 2-3 change mems from 2-3 to 1-2
> 1-2 rebind task1's mpol
> 1-2 set new bits
> 1-2 change mems from 0-1 to 0
> 1-2 rebind task1's mpol
> 0-1 set new bits
> alloc on node2? NO 0-1
> ...
> can't alloc page
> goto oom
>
One of the major reasons why changing cpuset.mems can take >30s is because
of lengthy delays in the page allocator because it continuously loops
while trying reclaim or killing a thread and trying to allocate a page.
I think we should be able to optimize this by dropping it when it's not
required and moving it to get_page_from_freelist() which is the only thing
that cares about cpuset_zone_allowed_softwall().
Something like this:
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1643,17 +1643,29 @@ static void zlc_clear_zones_full(struct zonelist *zonelist)
static struct page *
get_page_from_freelist(gfp_t gfp_mask, nodemask_t *nodemask, unsigned int order,
struct zonelist *zonelist, int high_zoneidx, int alloc_flags,
- struct zone *preferred_zone, int migratetype)
+ struct zone **preferred_zone, int migratetype)
{
struct zoneref *z;
struct page *page = NULL;
int classzone_idx;
struct zone *zone;
- nodemask_t *allowednodes = NULL;/* zonelist_cache approximation */
+ nodemask_t *allowednodes = NULL;
int zlc_active = 0; /* set if using zonelist_cache */
int did_zlc_setup = 0; /* just call zlc_setup() one time */
- classzone_idx = zone_idx(preferred_zone);
+ get_mems_allowed();
+ /*
+ * preferred_zone must come from an allowed node if the allocation is
+ * constrained to either a mempolicy (nodemask != NULL) or otherwise
+ * limited by cpusets.
+ */
+ if (alloc_flags & ALLOC_CPUSET)
+ allowednodes = nodemask ? : &cpuset_current_mems_allowed;
+
+ first_zones_zonelist(zonelist, high_zoneidx, allowednodes,
+ preferred_zone);
+ classzone_idx = zone_idx(*preferred_zone);
+ allowednodes = NULL;
zonelist_scan:
/*
* Scan zonelist, looking for a zone with enough free.
@@ -1717,7 +1729,7 @@ zonelist_scan:
}
try_this_zone:
- page = buffered_rmqueue(preferred_zone, zone, order,
+ page = buffered_rmqueue(*preferred_zone, zone, order,
gfp_mask, migratetype);
if (page)
break;
@@ -1731,6 +1743,7 @@ this_zone_full:
zlc_active = 0;
goto zonelist_scan;
}
+ put_mems_allowed();
return page;
}
@@ -1832,7 +1845,7 @@ should_alloc_retry(gfp_t gfp_mask, unsigned int order,
static inline struct page *
__alloc_pages_may_oom(gfp_t gfp_mask, unsigned int order,
struct zonelist *zonelist, enum zone_type high_zoneidx,
- nodemask_t *nodemask, struct zone *preferred_zone,
+ nodemask_t *nodemask, struct zone **preferred_zone,
int migratetype)
{
struct page *page;
@@ -1885,13 +1898,13 @@ out:
static struct page *
__alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
struct zonelist *zonelist, enum zone_type high_zoneidx,
- nodemask_t *nodemask, int alloc_flags, struct zone *preferred_zone,
+ nodemask_t *nodemask, int alloc_flags, struct zone **preferred_zone,
int migratetype, unsigned long *did_some_progress,
bool sync_migration)
{
struct page *page;
- if (!order || compaction_deferred(preferred_zone))
+ if (!order || compaction_deferred(*preferred_zone))
return NULL;
current->flags |= PF_MEMALLOC;
@@ -1909,8 +1922,8 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
alloc_flags, preferred_zone,
migratetype);
if (page) {
- preferred_zone->compact_considered = 0;
- preferred_zone->compact_defer_shift = 0;
+ *preferred_zone->compact_considered = 0;
+ *preferred_zone->compact_defer_shift = 0;
count_vm_event(COMPACTSUCCESS);
return page;
}
@@ -1921,7 +1934,7 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
* but not enough to satisfy watermarks.
*/
count_vm_event(COMPACTFAIL);
- defer_compaction(preferred_zone);
+ defer_compaction(*preferred_zone);
cond_resched();
}
@@ -1932,7 +1945,7 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
static inline struct page *
__alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
struct zonelist *zonelist, enum zone_type high_zoneidx,
- nodemask_t *nodemask, int alloc_flags, struct zone *preferred_zone,
+ nodemask_t *nodemask, int alloc_flags, struct zone **preferred_zone,
int migratetype, unsigned long *did_some_progress,
bool sync_migration)
{
@@ -1944,7 +1957,7 @@ __alloc_pages_direct_compact(gfp_t gfp_mask, unsigned int order,
static inline struct page *
__alloc_pages_direct_reclaim(gfp_t gfp_mask, unsigned int order,
struct zonelist *zonelist, enum zone_type high_zoneidx,
- nodemask_t *nodemask, int alloc_flags, struct zone *preferred_zone,
+ nodemask_t *nodemask, int alloc_flags, struct zone **preferred_zone,
int migratetype, unsigned long *did_some_progress)
{
struct page *page = NULL;
@@ -2001,7 +2014,7 @@ retry:
static inline struct page *
__alloc_pages_high_priority(gfp_t gfp_mask, unsigned int order,
struct zonelist *zonelist, enum zone_type high_zoneidx,
- nodemask_t *nodemask, struct zone *preferred_zone,
+ nodemask_t *nodemask, struct zone **preferred_zone,
int migratetype)
{
struct page *page;
@@ -2012,7 +2025,8 @@ __alloc_pages_high_priority(gfp_t gfp_mask, unsigned int order,
preferred_zone, migratetype);
if (!page && gfp_mask & __GFP_NOFAIL)
- wait_iff_congested(preferred_zone, BLK_RW_ASYNC, HZ/50);
+ wait_iff_congested(*preferred_zone, BLK_RW_ASYNC,
+ HZ/50);
} while (!page && (gfp_mask & __GFP_NOFAIL));
return page;
@@ -2075,7 +2089,7 @@ gfp_to_alloc_flags(gfp_t gfp_mask)
static inline struct page *
__alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
struct zonelist *zonelist, enum zone_type high_zoneidx,
- nodemask_t *nodemask, struct zone *preferred_zone,
+ nodemask_t *nodemask, struct zone **preferred_zone,
int migratetype)
{
const gfp_t wait = gfp_mask & __GFP_WAIT;
@@ -2110,7 +2124,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
restart:
if (!(gfp_mask & __GFP_NO_KSWAPD))
wake_all_kswapd(order, zonelist, high_zoneidx,
- zone_idx(preferred_zone));
+ zone_idx(*preferred_zone));
/*
* OK, we're below the kswapd watermark and have kicked background
@@ -2119,14 +2133,6 @@ restart:
*/
alloc_flags = gfp_to_alloc_flags(gfp_mask);
- /*
- * Find the true preferred zone if the allocation is unconstrained by
- * cpusets.
- */
- if (!(alloc_flags & ALLOC_CPUSET) && !nodemask)
- first_zones_zonelist(zonelist, high_zoneidx, NULL,
- &preferred_zone);
-
rebalance:
/* This is the last chance, in general, before the goto nopage. */
page = get_page_from_freelist(gfp_mask, nodemask, order, zonelist,
@@ -2220,7 +2226,7 @@ rebalance:
pages_reclaimed += did_some_progress;
if (should_alloc_retry(gfp_mask, order, pages_reclaimed)) {
/* Wait for some write requests to complete then retry */
- wait_iff_congested(preferred_zone, BLK_RW_ASYNC, HZ/50);
+ wait_iff_congested(*preferred_zone, BLK_RW_ASYNC, HZ/50);
goto rebalance;
} else {
/*
@@ -2277,25 +2283,17 @@ __alloc_pages_nodemask(gfp_t gfp_mask, unsigned int order,
if (unlikely(!zonelist->_zonerefs->zone))
return NULL;
- get_mems_allowed();
- /* The preferred zone is used for statistics later */
- first_zones_zonelist(zonelist, high_zoneidx,
- nodemask ? : &cpuset_current_mems_allowed,
- &preferred_zone);
- if (!preferred_zone) {
- put_mems_allowed();
- return NULL;
- }
-
/* First allocation attempt */
page = get_page_from_freelist(gfp_mask|__GFP_HARDWALL, nodemask, order,
zonelist, high_zoneidx, ALLOC_WMARK_LOW|ALLOC_CPUSET,
- preferred_zone, migratetype);
- if (unlikely(!page))
+ &preferred_zone, migratetype);
+ if (unlikely(!page)) {
+ if (!preferred_zone)
+ return NULL;
page = __alloc_pages_slowpath(gfp_mask, order,
zonelist, high_zoneidx, nodemask,
- preferred_zone, migratetype);
- put_mems_allowed();
+ &preferred_zone, migratetype);
+ }
trace_mm_page_alloc(page, order, gfp_mask, migratetype);
return page;
This would significantly reduce the amount of time that it takes to write
to cpuset.mems because we drop get_mems_allowed() between allocation
attempts. We really, really want to do this anyway because it's possible
that a cpuset is being expanded to a larger set of nodes and they are
inaccessible to concurrent memory allocations because the page allocator
is holding get_mems_allowed() while looping and trying to find more
memory.
Comments?
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