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Subject[PATCH] mm: SLAB Out-of-memory diagnostics
Following the example at mm/slub.c, add out-of-memory diagnostics to the SLAB
allocator to help on debugging OOM conditions. This patch also adds a new
sysctl, 'oom_dump_slabs_forced', that overrides the effect of __GFP_NOWARN page
allocation flag and forces the kernel to report every slab allocation failure.

An example print out looks like this:

<snip page allocator out-of-memory message>
SLAB: Unable to allocate memory on node 0 (gfp=0x11200)
cache: bio-0, object size: 192, order: 0
node0: slabs: 3/3, objs: 60/60, free: 0

Signed-off-by: Rafael Aquini <aquini@redhat.com>
---
Documentation/sysctl/vm.txt | 23 ++++++++++++++++++
include/linux/slab.h | 2 +
kernel/sysctl.c | 9 +++++++
mm/slab.c | 55 ++++++++++++++++++++++++++++++++++++++++++-
4 files changed, 88 insertions(+), 1 deletions(-)
diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt
index 96f0ee8..75bdf91 100644
--- a/Documentation/sysctl/vm.txt
+++ b/Documentation/sysctl/vm.txt
@@ -498,6 +498,29 @@ this is causing problems for your system/application.

==============================================================

+oom_dump_slabs_forced
+
+Overrides the effects of __GFP_NOWARN page allocation flag, thus forcing
+the system to print warnings about every allocation failure for the
+slab allocator, and helping on debugging certain OOM conditions.
+The print out is pretty similar, and complements data that is reported by
+the page allocator out-of-memory warning:
+
+<snip page allocator out-of-memory message>
+ SLAB: Unable to allocate memory on node 0 (gfp=0x11200)
+ cache: bio-0, object size: 192, order: 0
+ node0: slabs: 3/3, objs: 60/60, free: 0
+
+If this is set to zero, the default behavior is observed and warnings will only
+be printed out for allocation requests that didn't set the __GFP_NOWARN flag.
+
+When set to non-zero, this information is shown whenever the allocator finds
+itself failing to grant a request, regardless the __GFP_NOWARN flag status.
+
+The default value is 0 (disabled).
+
+==============================================================
+
oom_dump_tasks

Enables a system-wide task dump (excluding kernel threads) to be
diff --git a/include/linux/slab.h b/include/linux/slab.h
index 573c809..ca57021 100644
--- a/include/linux/slab.h
+++ b/include/linux/slab.h
@@ -353,4 +353,6 @@ static inline void *kzalloc_node(size_t size, gfp_t flags, int node)

void __init kmem_cache_init_late(void);

+/* sysctl */
+extern int sysctl_oom_dump_slabs;
#endif /* _LINUX_SLAB_H */
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index f487f25..71fe8ec 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1040,6 +1040,15 @@ static struct ctl_table vm_table[] = {
.mode = 0644,
.proc_handler = proc_dointvec,
},
+#if defined(CONFIG_SLAB)
+ {
+ .procname = "oom_dump_slabs_forced",
+ .data = &sysctl_oom_dump_slabs,
+ .maxlen = sizeof(sysctl_oom_dump_slabs),
+ .mode = 0644,
+ .proc_handler = proc_dointvec,
+ },
+#endif
{
.procname = "overcommit_ratio",
.data = &sysctl_overcommit_ratio,
diff --git a/mm/slab.c b/mm/slab.c
index f0bd785..993ca4c 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -168,6 +168,9 @@
SLAB_DEBUG_OBJECTS | SLAB_NOLEAKTRACE | SLAB_NOTRACK)
#endif

+/* sysctl */
+int sysctl_oom_dump_slabs = 0;
+
/*
* kmem_bufctl_t:
*
@@ -1731,6 +1734,52 @@ static int __init cpucache_init(void)
}
__initcall(cpucache_init);

+static noinline void
+slab_out_of_memory(struct kmem_cache *cachep, gfp_t gfpflags, int nodeid)
+{
+ struct kmem_list3 *l3;
+ struct slab *slabp;
+ unsigned long flags;
+ int node;
+
+ printk(KERN_WARNING
+ "SLAB: Unable to allocate memory on node %d (gfp=0x%x)\n",
+ nodeid, gfpflags);
+ printk(KERN_WARNING " cache: %s, object size: %d, order: %d\n",
+ cachep->name, cachep->buffer_size, cachep->gfporder);
+
+ for_each_online_node(node) {
+ unsigned long active_objs = 0, num_objs = 0, free_objects = 0;
+ unsigned long active_slabs = 0, num_slabs = 0;
+
+ l3 = cachep->nodelists[node];
+ if (!l3)
+ continue;
+
+ spin_lock_irqsave(&l3->list_lock, flags);
+ list_for_each_entry(slabp, &l3->slabs_full, list) {
+ active_objs += cachep->num;
+ active_slabs++;
+ }
+ list_for_each_entry(slabp, &l3->slabs_partial, list) {
+ active_objs += slabp->inuse;
+ active_slabs++;
+ }
+ list_for_each_entry(slabp, &l3->slabs_free, list)
+ num_slabs++;
+
+ free_objects += l3->free_objects;
+ spin_unlock_irqrestore(&l3->list_lock, flags);
+
+ num_slabs += active_slabs;
+ num_objs = num_slabs * cachep->num;
+ printk(KERN_WARNING
+ " node%d: slabs: %ld/%ld, objs: %ld/%ld, free: %ld\n",
+ node, active_slabs, num_slabs, active_objs, num_objs,
+ free_objects);
+ }
+}
+
/*
* Interface to system's page allocator. No need to hold the cache-lock.
*
@@ -1757,8 +1806,12 @@ static void *kmem_getpages(struct kmem_cache *cachep, gfp_t flags, int nodeid)
flags |= __GFP_RECLAIMABLE;

page = alloc_pages_exact_node(nodeid, flags | __GFP_NOTRACK, cachep->gfporder);
- if (!page)
+ if (!page) {
+ if ((sysctl_oom_dump_slabs || !(flags & __GFP_NOWARN)) &&
+ printk_ratelimit())
+ slab_out_of_memory(cachep, flags, nodeid);
return NULL;
+ }

nr_pages = (1 << cachep->gfporder);
if (cachep->flags & SLAB_RECLAIM_ACCOUNT)
--
1.7.7.6


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