On Wed, Sep 12, 2012 at 02:20:19PM -0700, Andrew Morton wrote:
> On Wed, 12 Sep 2012 02:48:40 +0200
> Andrea Arcangeli <aarcange@xxxxxxxxxx> wrote:
>
> > On Tue, Sep 11, 2012 at 04:34:55PM -0700, Andrew Morton wrote:
> > > On Mon, 10 Sep 2012 09:18:30 +0800
> > > Shaohua Li <shli@xxxxxxxxxx> wrote:
> > >
> > > > isolate_migratepages_range() might isolate none pages, for example, when
> > > > zone->lru_lock is contended and compaction is async. In this case, we should
> > > > abort compaction, otherwise, compact_zone will run a useless loop and make
> > > > zone->lru_lock is even contended.
> > > >
> > > > ...
> > > >
> > > > @@ -838,12 +838,14 @@ static unsigned long compact_zone_order(
> > > > .migratetype = allocflags_to_migratetype(gfp_mask),
> > > > .zone = zone,
> > > > .sync = sync,
> > > > - .contended = contended,
> > > > };
> > > > INIT_LIST_HEAD(&cc.freepages);
> > > > INIT_LIST_HEAD(&cc.migratepages);
> > > >
> > > > - return compact_zone(zone, &cc);
> > > > + ret = compact_zone(zone, &cc);
> > > > + if (contended)
> > > > + *contended = cc.contended;
> > > > + return ret;
> > > > }
> > > >
> > >
> > > From a quick read, `contended' is never NULL here. And defining the
> >
> > "contended" pointer can be null with some caller so the if is
> > needed. The inner code was checking it before. This is also why we
> > couldn't use *contended for the loop break bugfix, because contended
> > could have been null at times.
>
> Confused. I can see only two call sites:
> __alloc_pages_slowpath
> ->__alloc_pages_direct_compact
> ->try_to_compact_pages
> ->compact_zone_order
> and in both cases, `contended' points at valid storage.
>
Andrea encountered out an additional bug as well but I preferred
a variant of Minchan's fix for it. Can you replace patches
mm-compaction-abort-compaction-loop-if-lock-is-contended-or-run-too-long.patch
mm-compaction-abort-compaction-loop-if-lock-is-contended-or-run-too-long-fix.patch
with this version please? FWIW, I've asked Richard Davies (added to cc)
to test with this version of the patch as he is also reporting contention
problems when booting a windows guest under qemu.
I see you already picked up the documentation patch so I'll ignore the
additional "poke poke" in your mail :)
---8<---
From: Shaohua Li <shli@xxxxxxxxxxxx>
Subject: [PATCH] compaction: abort compaction loop if lock is contended or run too long
Changelog since V2
o Fix BUG_ON triggered due to pages left on cc.migratepages
o Make compact_zone_order() require non-NULL arg `contended'
Changelog since V1
o only abort the compaction if lock is contended or run too long
o Rearranged the code by Andrea Arcangeli.
isolate_migratepages_range() might isolate no pages if for example when
zone->lru_lock is contended and running asynchronous compaction. In this
case, we should abort compaction, otherwise, compact_zone will run a
useless loop and make zone->lru_lock is even contended. An additional
check is added to ensure that cc.migratepages and cc.freepages get
properly drained whan compaction is aborted.
[minchan@xxxxxxxxxx: Putback pages isolated for migration if aborting]
[akpm@xxxxxxxxxxxxxxxxxxxx: compact_zone_order requires non-NULL arg contended]
Signed-off-by: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Signed-off-by: Shaohua Li <shli@xxxxxxxxxxxx>
Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
---
mm/compaction.c | 17 ++++++++++++-----
mm/internal.h | 2 +-
2 files changed, 13 insertions(+), 6 deletions(-)
diff --git a/mm/compaction.c b/mm/compaction.c
index 7fcd3a5..a8de20d 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -70,8 +70,7 @@ static bool compact_checklock_irqsave(spinlock_t *lock, unsigned long *flags,
/* async aborts if taking too long or contended */
if (!cc->sync) {
- if (cc->contended)
- *cc->contended = true;
+ cc->contended = true;
return false;
}
@@ -634,7 +633,7 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone,
/* Perform the isolation */
low_pfn = isolate_migratepages_range(zone, cc, low_pfn, end_pfn);
- if (!low_pfn)
+ if (!low_pfn || cc->contended)
return ISOLATE_ABORT;
cc->migrate_pfn = low_pfn;
@@ -787,6 +786,8 @@ static int compact_zone(struct zone *zone, struct compact_control *cc)
switch (isolate_migratepages(zone, cc)) {
case ISOLATE_ABORT:
ret = COMPACT_PARTIAL;
+ putback_lru_pages(&cc->migratepages);
+ cc->nr_migratepages = 0;
goto out;
case ISOLATE_NONE:
continue;
@@ -831,6 +832,7 @@ static unsigned long compact_zone_order(struct zone *zone,
int order, gfp_t gfp_mask,
bool sync, bool *contended)
{
+ unsigned long ret;
struct compact_control cc = {
.nr_freepages = 0,
.nr_migratepages = 0,
@@ -838,12 +840,17 @@ static unsigned long compact_zone_order(struct zone *zone,
.migratetype = allocflags_to_migratetype(gfp_mask),
.zone = zone,
.sync = sync,
- .contended = contended,
};
INIT_LIST_HEAD(&cc.freepages);
INIT_LIST_HEAD(&cc.migratepages);
- return compact_zone(zone, &cc);
+ ret = compact_zone(zone, &cc);
+
+ VM_BUG_ON(!list_empty(&cc.freepages));
+ VM_BUG_ON(!list_empty(&cc.migratepages));
+
+ *contended = cc.contended;
+ return ret;
}
int sysctl_extfrag_threshold = 500;
diff --git a/mm/internal.h b/mm/internal.h
index b8c91b3..4bd7c0e 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -130,7 +130,7 @@ struct compact_control {
int order; /* order a direct compactor needs */
int migratetype; /* MOVABLE, RECLAIMABLE etc */
struct zone *zone;
- bool *contended; /* True if a lock was contended */
+ bool contended; /* True if a lock was contended */
};
unsigned long
--
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