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Subject[PATCH 3/3] mm: oom: show unreclaimable slab info when unreclaimable slabs > user memory
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
unreclaimable slabs amount is greater than total user memory (LRU
pages).

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 | 22 ++++++++++++++++++++++
mm/slab.h | 2 ++
mm/slab_common.c | 32 ++++++++++++++++++++++++++++++++
3 files changed, 56 insertions(+)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 99736e0..6d89397 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>
@@ -160,6 +161,25 @@ static bool oom_unkillable_task(struct task_struct *p,
return false;
}

+/*
+ * Print out unreclaimble slabs info when unreclaimable slabs amount is greater
+ * than all user memory (LRU pages)
+ */
+static bool is_dump_unreclaim_slabs(void)
+{
+ unsigned long nr_lru;
+
+ nr_lru = global_node_page_state(NR_ACTIVE_ANON) +
+ global_node_page_state(NR_INACTIVE_ANON) +
+ global_node_page_state(NR_ACTIVE_FILE) +
+ global_node_page_state(NR_INACTIVE_FILE) +
+ global_node_page_state(NR_ISOLATED_ANON) +
+ global_node_page_state(NR_ISOLATED_FILE) +
+ global_node_page_state(NR_UNEVICTABLE);
+
+ return (global_node_page_state(NR_SLAB_UNRECLAIMABLE) > nr_lru);
+}
+
/**
* oom_badness - heuristic function to determine which candidate task to kill
* @p: task struct of which task we should calculate
@@ -423,6 +443,8 @@ static void dump_header(struct oom_control *oc, struct task_struct *p)
mem_cgroup_print_oom_info(oc->memcg, p);
else
show_mem(SHOW_MEM_FILTER_NODES, oc->nodemask);
+ if (is_dump_unreclaim_slabs())
+ dump_unreclaimable_slab();
if (sysctl_oom_dump_tasks)
dump_tasks(oc->memcg, oc->nodemask);
}
diff --git a/mm/slab.h b/mm/slab.h
index 0733628..6fc4d5d 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -505,6 +505,8 @@ 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);

+void dump_unreclaimable_slab(void);
+
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 5520a22..be24324 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -1270,6 +1270,38 @@ static int slab_show(struct seq_file *m, void *p)
return 0;
}

+void dump_unreclaimable_slab(void)
+{
+ struct kmem_cache *s, *s2;
+ struct slabinfo sinfo;
+
+ pr_info("Unreclaimable slab info:\n");
+ pr_info("Name Used Total\n");
+
+ /*
+ * Here acquiring slab_mutex is risky since we don't prefer to get
+ * sleep in oom path. But, without mutex hold, it may introduce a
+ * risk of crash.
+ * Use mutex_trylock to protect the list traverse, dump nothing
+ * without acquiring the mutex.
+ */
+ if (!mutex_trylock(&slab_mutex))
+ return;
+ list_for_each_entry_safe(s, s2, &slab_caches, list) {
+ if (!is_root_cache(s) || (s->flags & SLAB_RECLAIM_ACCOUNT))
+ continue;
+
+ memset(&sinfo, 0, sizeof(sinfo));
+ get_slabinfo(s, &sinfo);
+
+ if (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);
+ }
+ mutex_unlock(&slab_mutex);
+}
+
#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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