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Subject[PATCH 2/2] mm: oom: show unreclaimable slab info when kernel panic
Date
Kernel may panic when oom happens without killable process sometimes it
is caused by huge unreclaimable slabs used by kernel.

Although kdump could help debug such problem, however, kdump is not
available on all architectures and it might be malfunction sometime.
And, since kernel already panic it is worthy capturing such information
in dmesg to aid touble shooting.

Print out unreclaimable slab info (used size and total size) which
actual memory usage is not zero (num_objs * size != 0) when panic_on_oom is set
or no killable process. Since such information is just showed when kernel
panic, so it will not lead too verbose message for normal oom.

The output looks like:

Unreclaimable slab info:
Name Used Total
rpc_buffers 31KB 31KB
rpc_tasks 7KB 7KB
ebitmap_node 1964KB 1964KB
avtab_node 5024KB 5024KB
xfs_buf 1402KB 1402KB
xfs_ili 134KB 134KB
xfs_efi_item 115KB 115KB
xfs_efd_item 115KB 115KB
xfs_buf_item 134KB 134KB
xfs_log_item_desc 342KB 342KB
xfs_trans 1412KB 1412KB
xfs_ifork 212KB 212KB

Signed-off-by: Yang Shi <yang.s@alibaba-inc.com>
---
mm/oom_kill.c | 3 +++
mm/slab.h | 8 ++++++++
mm/slab_common.c | 26 ++++++++++++++++++++++++++
3 files changed, 37 insertions(+)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 99736e0..bd48d34 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -43,6 +43,7 @@

#include <asm/tlb.h>
#include "internal.h"
+#include "slab.h"

#define CREATE_TRACE_POINTS
#include <trace/events/oom.h>
@@ -960,6 +961,7 @@ static void check_panic_on_oom(struct oom_control *oc,
if (is_sysrq_oom(oc))
return;
dump_header(oc, NULL);
+ dump_unreclaimable_slab();
panic("Out of memory: %s panic_on_oom is enabled\n",
sysctl_panic_on_oom == 2 ? "compulsory" : "system-wide");
}
@@ -1044,6 +1046,7 @@ bool out_of_memory(struct oom_control *oc)
/* Found nothing?!?! Either we hang forever, or we panic. */
if (!oc->chosen && !is_sysrq_oom(oc) && !is_memcg_oom(oc)) {
dump_header(oc, NULL);
+ dump_unreclaimable_slab();
panic("Out of memory and no killable processes...\n");
}
if (oc->chosen && oc->chosen != (void *)-1UL) {
diff --git a/mm/slab.h b/mm/slab.h
index 0733628..734a92d 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -505,6 +505,14 @@ static inline struct kmem_cache_node *get_node(struct kmem_cache *s, int node)
void memcg_slab_stop(struct seq_file *m, void *p);
int memcg_slab_show(struct seq_file *m, void *p);

+#ifdef CONFIG_SLABINFO
+void dump_unreclaimable_slab(void);
+#else
+void dump_unreclaimable_slab(void);
+{
+}
+#endif
+
void ___cache_free(struct kmem_cache *cache, void *x, unsigned long addr);

#ifdef CONFIG_SLAB_FREELIST_RANDOM
diff --git a/mm/slab_common.c b/mm/slab_common.c
index 904a83b..90d9de3 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -1272,6 +1272,32 @@ static int slab_show(struct seq_file *m, void *p)
return 0;
}

+void dump_unreclaimable_slab(void)
+{
+ struct kmem_cache *s;
+ struct slabinfo sinfo;
+
+ pr_info("Unreclaimable slab info:\n");
+ pr_info("Name Used Total\n");
+
+ /*
+ * Here acquiring slab_mutex is unnecessary since we don't prefer to
+ * get sleep in oom path right before kernel panic, and avoid race condition.
+ * Since it is already oom, so there should be not any big allocation
+ * which could change the statistics significantly.
+ */
+ list_for_each_entry(s, &slab_caches, list) {
+ if (!is_root_cache(s))
+ continue;
+
+ memset(&sinfo, 0, sizeof(sinfo));
+ get_slabinfo(s, &sinfo);
+
+ if (!(s->flags & SLAB_RECLAIM_ACCOUNT) && sinfo.num_objs > 0)
+ pr_info("%-17s %10luKB %10luKB\n", cache_name(s), (sinfo.active_objs * s->size) / 1024, (sinfo.num_objs * s->size) / 1024);
+ }
+}
+
#if defined(CONFIG_MEMCG) && !defined(CONFIG_SLOB)
void *memcg_slab_start(struct seq_file *m, loff_t *pos)
{
--
1.8.3.1
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