Re: [PATCH 2/2] mm: oom: dump single excessive slab cache when oom

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On 10/26/17 7:53 AM, Michal Hocko wrote:
On Thu 26-10-17 06:49:00, Yang Shi wrote:
Per the discussion with David [1], it looks more reasonable to just dump

Please try to avoid external references in the changelog as much as
possible.

OK.


the single excessive slab cache instead of dumping all slab caches when
oom.

You meant to say
"to just dump all slab caches which excess 10% of the total memory."

While we are at it. Abusing calc_mem_size seems to be rather clumsy and
tt is not nodemask aware so you the whole thing is dubious for NUMA
constrained OOMs.

Since we just need the total memory size of the node for NUMA constrained OOM, we should be able to use show_mem_node_skip() to bring in nodemask.


The more I think about this the more I am convinced that this is just
fiddling with the code without a good reason and without much better
outcome.

I don't get you. Do you mean the benefit is not that much with just dumping excessive slab caches?

Thanks,
Yang


Dump single excessive slab cache if its size is > 10% of total system

s@single@all@

memory size when oom regardless it is unreclaimable.

[1] https://marc.info/?l=linux-mm&m=150819933626604&w=2

Suggested-by: David Rientjes <rientjes@xxxxxxxxxx>
Signed-off-by: Yang Shi <yang.s@xxxxxxxxxxxxxxx>
---
  mm/oom_kill.c    | 22 +---------------------
  mm/slab.h        |  4 ++--
  mm/slab_common.c | 21 ++++++++++++++++-----
  3 files changed, 19 insertions(+), 28 deletions(-)

diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 26add8a..f996f29 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -162,25 +162,6 @@ 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
@@ -443,8 +424,7 @@ 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();
+		dump_slab_cache();
  	}
  	if (sysctl_oom_dump_tasks)
  		dump_tasks(oc->memcg, oc->nodemask);
diff --git a/mm/slab.h b/mm/slab.h
index 6a86025..818b569 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -507,9 +507,9 @@ static inline struct kmem_cache_node *get_node(struct kmem_cache *s, int node)
  int memcg_slab_show(struct seq_file *m, void *p);
#if defined(CONFIG_SLAB) || defined(CONFIG_SLUB_DEBUG)
-void dump_unreclaimable_slab(void);
+void dump_slab_cache(void);
  #else
-static inline void dump_unreclaimable_slab(void)
+static inline void dump_slab_cache(void)
  {
  }
  #endif
diff --git a/mm/slab_common.c b/mm/slab_common.c
index 1b14fe0..e5bfa07 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -1311,7 +1311,18 @@ static int slab_show(struct seq_file *m, void *p)
  	return 0;
  }
-void dump_unreclaimable_slab(void)
+static bool inline is_dump_slabs(struct kmem_cache *s, struct slabinfo *sinfo)
+{
+	unsigned long total = 0, reserved = 0, highmem = 0;
+	unsigned long slab_size = sinfo->num_objs * s->size;
+
+	calc_mem_size(&total, &reserved, &highmem);
+
+	/* Check if single slab > 10% of total memory size */
+	return (slab_size > (total * PAGE_SIZE / 10));
+}
+
+void dump_slab_cache(void)
  {
  	struct kmem_cache *s, *s2;
  	struct slabinfo sinfo;
@@ -1324,20 +1335,20 @@ void dump_unreclaimable_slab(void)
  	 * without acquiring the mutex.
  	 */
  	if (!mutex_trylock(&slab_mutex)) {
-		pr_warn("excessive unreclaimable slab but cannot dump stats\n");
+		pr_warn("excessive slab cache but cannot dump stats\n");
  		return;
  	}
- pr_info("Unreclaimable slab info:\n");
+	pr_info("The list of excessive single slab cache:\n");
  	pr_info("Name                      Used          Total\n");
list_for_each_entry_safe(s, s2, &slab_caches, list) {
-		if (!is_root_cache(s) || (s->flags & SLAB_RECLAIM_ACCOUNT))
+		if (!is_root_cache(s))
  			continue;
get_slabinfo(s, &sinfo); - if (sinfo.num_objs > 0)
+		if (is_dump_slabs(s, &sinfo))
  			pr_info("%-17s %10luKB %10luKB\n", cache_name(s),
  				(sinfo.active_objs * s->size) / 1024,
  				(sinfo.num_objs * s->size) / 1024);
--
1.8.3.1


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