[PATCH 0/3 v8] oom: capture unreclaimable slab info in oom message

[PATCH 0/3 v8] oom: capture unreclaimable slab info in oom message

[Yang Shi]

Recently we ran into a oom issue, kernel panic due to no killable process.
The dmesg shows huge unreclaimable slabs used almost 100% memory, but kdump doesn't capture vmcore due to some reason.

So, it may sound better to capture unreclaimable slab info in oom message when kernel panic to aid trouble shooting and cover the corner case.
Since kernel already panic, so capturing more information sounds worthy and doesn't bother normal oom killer.

With the patchset, tools/vm/slabinfo has a new option, "-U", to show unreclaimable slab only.

And, oom will print all non zero (num_objs * size != 0) unreclaimable slabs in oom killer message.

For details, please see the commit log for each commit.

Changelog v8 a??> 9:
* Adopted Tetsuoa??s suggestion to protect global slab list traverse with mutex_trylock() to prevent from sleeping. Without the mutex acquired unreclaimable slbas will not be dumped.
* Adopted the suggestion from Christoph to dump CONFIG_SLABINFO since it is pointless to keep it.
* Rebased to 4.13-rc3

Changelog v7 a??> v8:
* Adopted Michala??s suggestion to dump unreclaim slab info when unreclaimable slabs amount > total user memory. Not only in oom panic path.

Changelog v6 -> v7:
* Added unreclaim_slabs_oom_ratio proc knob, unreclaimable slabs info will be dumped when unreclaimable slabs amount : all user memory > the ratio

Changelog v5 a??> v6:
* Fixed a checkpatch.pl warning for patch #2

Changelog v4 a??> v5:
* Solved the comments from David
* Build test SLABINFO = n

Changelog v3 a??> v4:
* Solved the comments from David
* Added Davida??s Acked-by in patch 1

Changelog v2 a??> v3:
* Show used size and total size of each kmem cache per Davida??s comment

Changelog v1 a??> v2:
* Removed the original patch 1 (a??mm: slab: output reclaimable flag in /proc/slabinfoa??) since Christoph suggested it might break the compatibility and /proc/slabinfo is legacy
* Added Christopha??s Acked-by
* Removed acquiring slab_mutex per Tetsuoa??s comment


Yang Shi (3):
      tools: slabinfo: add "-U" option to show unreclaimable slabs only
      mm: slabinfo: dump CONFIG_SLABINFO
      mm: oom: show unreclaimable slab info when unreclaimable slabs > user memory

 init/Kconfig        |  6 ------
 mm/memcontrol.c     |  2 --
 mm/oom_kill.c       | 22 ++++++++++++++++++++++
 mm/slab.c           |  2 --
 mm/slab.h           |  2 ++
 mm/slab_common.c    | 35 ++++++++++++++++++++++++++++++++---
 mm/slub.c           |  2 --
 tools/vm/slabinfo.c | 11 ++++++++++-
 8 files changed, 66 insertions(+), 16 deletions(-)

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[PATCH 1/3] tools: slabinfo: add "-U" option to show unreclaimable slabs only

[Yang Shi]

Add "-U" option to show unreclaimable slabs only.

"-U" and "-S" together can tell us what unreclaimable slabs use the most
memory to help debug huge unreclaimable slabs issue.

Signed-off-by: Yang Shi <yang.s@alibaba-inc.com>
Acked-by: Christoph Lameter <cl@linux.com>
Acked-by: David Rientjes <rientjes@google.com>
---
 tools/vm/slabinfo.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/tools/vm/slabinfo.c b/tools/vm/slabinfo.c
index b9d34b3..de8fa11 100644
--- a/tools/vm/slabinfo.c
+++ b/tools/vm/slabinfo.c
@@ -83,6 +83,7 @@ struct aliasinfo {
 int sort_loss;
 int extended_totals;
 int show_bytes;
+int unreclaim_only;
 
 /* Debug options */
 int sanity;
@@ -132,6 +133,7 @@ static void usage(void)
 		"-L|--Loss              Sort by loss\n"
 		"-X|--Xtotals           Show extended summary information\n"
 		"-B|--Bytes             Show size in bytes\n"
+		"-U|--Unreclaim		Show unreclaimable slabs only\n"
 		"\nValid debug options (FZPUT may be combined)\n"
 		"a / A          Switch on all debug options (=FZUP)\n"
 		"-              Switch off all debug options\n"
@@ -568,6 +570,9 @@ static void slabcache(struct slabinfo *s)
 	if (strcmp(s->name, "*") == 0)
 		return;
 
+	if (unreclaim_only && s->reclaim_account)
+		return;
+
 	if (actual_slabs == 1) {
 		report(s);
 		return;
@@ -1346,6 +1351,7 @@ struct option opts[] = {
 	{ "Loss", no_argument, NULL, 'L'},
 	{ "Xtotals", no_argument, NULL, 'X'},
 	{ "Bytes", no_argument, NULL, 'B'},
+	{ "Unreclaim", no_argument, NULL, 'U'},
 	{ NULL, 0, NULL, 0 }
 };
 
@@ -1357,7 +1363,7 @@ int main(int argc, char *argv[])
 
 	page_size = getpagesize();
 
-	while ((c = getopt_long(argc, argv, "aAd::Defhil1noprstvzTSN:LXB",
+	while ((c = getopt_long(argc, argv, "aAd::Defhil1noprstvzTSN:LXBU",
 						opts, NULL)) != -1)
 		switch (c) {
 		case '1':
@@ -1438,6 +1444,9 @@ int main(int argc, char *argv[])
 		case 'B':
 			show_bytes = 1;
 			break;
+		case 'U':
+			unreclaim_only = 1;
+			break;
 		default:
 			fatal("%s: Invalid option '%c'\n", argv[0], optopt);
 
-- 
1.8.3.1

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[PATCH 2/3] mm: slabinfo: dump CONFIG_SLABINFO

[Yang Shi]

According to the discussion with Christoph [1], it sounds it is pointless
to keep CONFIG_SLABINFO around.

This patch just remove CONFIG_SLABINFO config option, but /proc/slabinfo
is still available.

[1] https://marc.info/?l=linux-kernel&m=150695909709711&w=2

Signed-off-by: Yang Shi <yang.s@alibaba-inc.com>
---
 init/Kconfig     | 6 ------
 mm/memcontrol.c  | 2 --
 mm/slab.c        | 2 --
 mm/slab_common.c | 3 ---
 mm/slub.c        | 2 --
 5 files changed, 15 deletions(-)

diff --git a/init/Kconfig b/init/Kconfig
index 78cb246..5d3c80a 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1657,12 +1657,6 @@ config HAVE_GENERIC_DMA_COHERENT
 	bool
 	default n
 
-config SLABINFO
-	bool
-	depends on PROC_FS
-	depends on SLAB || SLUB_DEBUG
-	default y
-
 config RT_MUTEXES
 	bool
 
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 15af3da..0a8ed72 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4039,7 +4039,6 @@ static ssize_t memcg_write_event_control(struct kernfs_open_file *of,
 		.write = mem_cgroup_reset,
 		.read_u64 = mem_cgroup_read_u64,
 	},
-#ifdef CONFIG_SLABINFO
 	{
 		.name = "kmem.slabinfo",
 		.seq_start = memcg_slab_start,
@@ -4047,7 +4046,6 @@ static ssize_t memcg_write_event_control(struct kernfs_open_file *of,
 		.seq_stop = memcg_slab_stop,
 		.seq_show = memcg_slab_show,
 	},
-#endif
 	{
 		.name = "kmem.tcp.limit_in_bytes",
 		.private = MEMFILE_PRIVATE(_TCP, RES_LIMIT),
diff --git a/mm/slab.c b/mm/slab.c
index 04dec48..5743a51 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -4096,7 +4096,6 @@ static void cache_reap(struct work_struct *w)
 	schedule_delayed_work(work, round_jiffies_relative(REAPTIMEOUT_AC));
 }
 
-#ifdef CONFIG_SLABINFO
 void get_slabinfo(struct kmem_cache *cachep, struct slabinfo *sinfo)
 {
 	unsigned long active_objs, num_objs, active_slabs;
@@ -4404,7 +4403,6 @@ static int __init slab_proc_init(void)
 	return 0;
 }
 module_init(slab_proc_init);
-#endif
 
 #ifdef CONFIG_HARDENED_USERCOPY
 /*
diff --git a/mm/slab_common.c b/mm/slab_common.c
index 904a83b..5520a22 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -1175,8 +1175,6 @@ void cache_random_seq_destroy(struct kmem_cache *cachep)
 }
 #endif /* CONFIG_SLAB_FREELIST_RANDOM */
 
-#ifdef CONFIG_SLABINFO
-
 #ifdef CONFIG_SLAB
 #define SLABINFO_RIGHTS (S_IWUSR | S_IRUSR)
 #else
@@ -1346,7 +1344,6 @@ static int __init slab_proc_init(void)
 	return 0;
 }
 module_init(slab_proc_init);
-#endif /* CONFIG_SLABINFO */
 
 static __always_inline void *__do_krealloc(const void *p, size_t new_size,
 					   gfp_t flags)
diff --git a/mm/slub.c b/mm/slub.c
index 163352c..74a8776 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -5851,7 +5851,6 @@ static int __init slab_sysfs_init(void)
 /*
  * The /proc/slabinfo ABI
  */
-#ifdef CONFIG_SLABINFO
 void get_slabinfo(struct kmem_cache *s, struct slabinfo *sinfo)
 {
 	unsigned long nr_slabs = 0;
@@ -5883,4 +5882,3 @@ ssize_t slabinfo_write(struct file *file, const char __user *buffer,
 {
 	return -EIO;
 }
-#endif /* CONFIG_SLABINFO */
-- 
1.8.3.1

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[PATCH 3/3] mm: oom: show unreclaimable slab info when unreclaimable slabs > user memory

[Yang Shi]

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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Re: [PATCH 0/3 v8] oom: capture unreclaimable slab info in oom message

[Yang Shi]

This round should be v9. Sorry for the typo.

Yang


On 10/3/17 11:06 AM, Yang Shi wrote:
> 
> Recently we ran into a oom issue, kernel panic due to no killable process.
> The dmesg shows huge unreclaimable slabs used almost 100% memory, but kdump doesn't capture vmcore due to some reason.
> 
> So, it may sound better to capture unreclaimable slab info in oom message when kernel panic to aid trouble shooting and cover the corner case.
> Since kernel already panic, so capturing more information sounds worthy and doesn't bother normal oom killer.
> 
> With the patchset, tools/vm/slabinfo has a new option, "-U", to show unreclaimable slab only.
> 
> And, oom will print all non zero (num_objs * size != 0) unreclaimable slabs in oom killer message.
> 
> For details, please see the commit log for each commit.
> 
> Changelog v8 a??> 9:
> * Adopted Tetsuoa??s suggestion to protect global slab list traverse with mutex_trylock() to prevent from sleeping. Without the mutex acquired unreclaimable slbas will not be dumped.
> * Adopted the suggestion from Christoph to dump CONFIG_SLABINFO since it is pointless to keep it.
> * Rebased to 4.13-rc3
> 
> Changelog v7 a??> v8:
> * Adopted Michala??s suggestion to dump unreclaim slab info when unreclaimable slabs amount > total user memory. Not only in oom panic path.
> 
> Changelog v6 -> v7:
> * Added unreclaim_slabs_oom_ratio proc knob, unreclaimable slabs info will be dumped when unreclaimable slabs amount : all user memory > the ratio
> 
> Changelog v5 a??> v6:
> * Fixed a checkpatch.pl warning for patch #2
> 
> Changelog v4 a??> v5:
> * Solved the comments from David
> * Build test SLABINFO = n
> 
> Changelog v3 a??> v4:
> * Solved the comments from David
> * Added Davida??s Acked-by in patch 1
> 
> Changelog v2 a??> v3:
> * Show used size and total size of each kmem cache per Davida??s comment
> 
> Changelog v1 a??> v2:
> * Removed the original patch 1 (a??mm: slab: output reclaimable flag in /proc/slabinfoa??) since Christoph suggested it might break the compatibility and /proc/slabinfo is legacy
> * Added Christopha??s Acked-by
> * Removed acquiring slab_mutex per Tetsuoa??s comment
> 
> 
> Yang Shi (3):
>        tools: slabinfo: add "-U" option to show unreclaimable slabs only
>        mm: slabinfo: dump CONFIG_SLABINFO
>        mm: oom: show unreclaimable slab info when unreclaimable slabs > user memory
> 
>   init/Kconfig        |  6 ------
>   mm/memcontrol.c     |  2 --
>   mm/oom_kill.c       | 22 ++++++++++++++++++++++
>   mm/slab.c           |  2 --
>   mm/slab.h           |  2 ++
>   mm/slab_common.c    | 35 ++++++++++++++++++++++++++++++++---
>   mm/slub.c           |  2 --
>   tools/vm/slabinfo.c | 11 ++++++++++-
>   8 files changed, 66 insertions(+), 16 deletions(-)
> 

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Re: [PATCH 3/3] mm: oom: show unreclaimable slab info when unreclaimable slabs > user memory

[Michal Hocko]

On Wed 04-10-17 02:06:17, Yang Shi wrote:
> +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);
> +}

I am sorry I haven't pointed this earlier (I was following only half
way) but this should really be memcg aware. You are checking only global
counters. I do not think it is an absolute must to provide per-memcg
data but you should at least check !is_memcg_oom(oc).

[...]
> +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;

I would move the trylock up so that we do not get empty and confusing
Unreclaimable slab info: and add a note that we are not dumping anything
due to lock contention
	pr_warn("excessive unreclaimable slab memory but cannot dump stats to give you more details\n");

Other than that this looks sensible to me.

> +	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

-- 
Michal Hocko
SUSE Labs

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Re: [PATCH 3/3] mm: oom: show unreclaimable slab info when unreclaimable slabs > user memory

[Yang Shi]

On 10/4/17 7:27 AM, Michal Hocko wrote:
> On Wed 04-10-17 02:06:17, Yang Shi wrote:
>> +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);
>> +}
> 
> I am sorry I haven't pointed this earlier (I was following only half
> way) but this should really be memcg aware. You are checking only global
> counters. I do not think it is an absolute must to provide per-memcg
> data but you should at least check !is_memcg_oom(oc).

OK, sure.

> 
> [...]
>> +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;
> 
> I would move the trylock up so that we do not get empty and confusing
> Unreclaimable slab info: and add a note that we are not dumping anything
> due to lock contention
> 	pr_warn("excessive unreclaimable slab memory but cannot dump stats to give you more details\n");

Thanks for pointing this. Will fix in new version.

Yang

> 
> Other than that this looks sensible to me.
> 
>> +	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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Re: [PATCH 3/3] mm: oom: show unreclaimable slab info when unreclaimable slabs > user memory

[Yang Shi]

On 10/4/17 7:27 AM, Michal Hocko wrote:
> On Wed 04-10-17 02:06:17, Yang Shi wrote:
>> +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);
>> +}
> 
> I am sorry I haven't pointed this earlier (I was following only half
> way) but this should really be memcg aware. You are checking only global
> counters. I do not think it is an absolute must to provide per-memcg
> data but you should at least check !is_memcg_oom(oc).

BTW, I saw there is already such check in dump_header that looks like 
the below code:

         if (oc->memcg)
                 mem_cgroup_print_oom_info(oc->memcg, p);
         else
                 show_mem(SHOW_MEM_FILTER_NODES, oc->nodemask);

I'm supposed it'd better to replace "oc->memcg" to "is_memcg_oom(oc)" 
since they do the same check and "is_memcg_oom" interface sounds preferable.

Then I'm going to move unreclaimable slabs dump to the "else" block.

Yang

> 
> [...]
>> +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;
> 
> I would move the trylock up so that we do not get empty and confusing
> Unreclaimable slab info: and add a note that we are not dumping anything
> due to lock contention
> 	pr_warn("excessive unreclaimable slab memory but cannot dump stats to give you more details\n");
> 
> Other than that this looks sensible to me.
> 
>> +	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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Re: [PATCH 3/3] mm: oom: show unreclaimable slab info when unreclaimable slabs > user memory

[Michal Hocko]

On Thu 05-10-17 02:08:48, Yang Shi wrote:
> 
> 
> On 10/4/17 7:27 AM, Michal Hocko wrote:
> > On Wed 04-10-17 02:06:17, Yang Shi wrote:
> > > +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);
> > > +}
> > 
> > I am sorry I haven't pointed this earlier (I was following only half
> > way) but this should really be memcg aware. You are checking only global
> > counters. I do not think it is an absolute must to provide per-memcg
> > data but you should at least check !is_memcg_oom(oc).
> 
> BTW, I saw there is already such check in dump_header that looks like the
> below code:
> 
>         if (oc->memcg)
>                 mem_cgroup_print_oom_info(oc->memcg, p);
>         else
>                 show_mem(SHOW_MEM_FILTER_NODES, oc->nodemask);
> 
> I'm supposed it'd better to replace "oc->memcg" to "is_memcg_oom(oc)" since
> they do the same check and "is_memcg_oom" interface sounds preferable.

Yes, is_memcg_oom is better

> Then I'm going to move unreclaimable slabs dump to the "else" block.

makes sense.
-- 
Michal Hocko
SUSE Labs

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