[PATCH 3/4] mm: Centralize & improve oom reporting in show_mem.c

Kent Overstreet
2022-04-21T23:48:50Z

This patch:
- Moves lib/show_mem.c to mm/show_mem.c
- Changes show_mem() to always report on slab usage
- Instead of reporting on all slabs, we only report on top 10 slabs,
and in sorted order
- Also reports on shrinkers, with the new shrinkers_to_text().

More OOM reporting can be moved to show_mem.c and improved, this patch
is only a small start.

Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>
---
lib/Makefile | 2 +-
mm/Makefile | 2 +-
mm/oom_kill.c | 23 ------------------
{lib => mm}/show_mem.c | 14 +++++++++++
mm/slab.h | 6 +++--
mm/slab_common.c | 53 +++++++++++++++++++++++++++++++++++-------
6 files changed, 65 insertions(+), 35 deletions(-)
rename {lib => mm}/show_mem.c (78%)

diff --git a/lib/Makefile b/lib/Makefile
index 31a3904eda..c5041d33d0 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -30,7 +30,7 @@ endif
lib-y := ctype.o string.o vsprintf.o cmdline.o \
rbtree.o radix-tree.o timerqueue.o xarray.o \
idr.o extable.o sha1.o irq_regs.o argv_split.o \
- flex_proportions.o ratelimit.o show_mem.o \
+ flex_proportions.o ratelimit.o \
is_single_threaded.o plist.o decompress.o kobject_uevent.o \
earlycpio.o seq_buf.o siphash.o dec_and_lock.o \
nmi_backtrace.o nodemask.o win_minmax.o memcat_p.o \
diff --git a/mm/Makefile b/mm/Makefile
index 70d4309c9c..97c0be12f3 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -54,7 +54,7 @@ obj-y := filemap.o mempool.o oom_kill.o fadvise.o \
mm_init.o percpu.o slab_common.o \
compaction.o vmacache.o \
interval_tree.o list_lru.o workingset.o \
- debug.o gup.o mmap_lock.o $(mmu-y)
+ debug.o gup.o mmap_lock.o show_mem.o $(mmu-y)

# Give 'page_alloc' its own module-parameter namespace
page-alloc-y := page_alloc.o
diff --git a/mm/oom_kill.c b/mm/oom_kill.c
index 832fb33037..659c7d6376 100644
--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -171,27 +171,6 @@ static bool oom_unkillable_task(struct task_struct *p)
return false;
}

-/*
- * Check whether unreclaimable slab amount is greater than
- * all user memory(LRU pages).
- * dump_unreclaimable_slab() could help in the case that
- * oom due to too much unreclaimable slab used by kernel.
-*/
-static bool should_dump_unreclaim_slab(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_pages(NR_SLAB_UNRECLAIMABLE_B) > nr_lru);
-}
-
/**
* oom_badness - heuristic function to determine which candidate task to kill
* @p: task struct of which task we should calculate
@@ -465,8 +444,6 @@ static void dump_header(struct oom_control *oc, struct task_struct *p)
mem_cgroup_print_oom_meminfo(oc->memcg);
else {
show_mem(SHOW_MEM_FILTER_NODES, oc->nodemask);
- if (should_dump_unreclaim_slab())
- dump_unreclaimable_slab();
}
if (sysctl_oom_dump_tasks)
dump_tasks(oc);
diff --git a/lib/show_mem.c b/mm/show_mem.c
similarity index 78%
rename from lib/show_mem.c
rename to mm/show_mem.c
index 1c26c14ffb..c9f37f13d6 100644
--- a/lib/show_mem.c
+++ b/mm/show_mem.c
@@ -7,11 +7,15 @@

#include <linux/mm.h>
#include <linux/cma.h>
+#include <linux/printbuf.h>
+
+#include "slab.h"

void show_mem(unsigned int filter, nodemask_t *nodemask)
{
pg_data_t *pgdat;
unsigned long total = 0, reserved = 0, highmem = 0;
+ struct printbuf buf = PRINTBUF;

printk("Mem-Info:\n");
show_free_areas(filter, nodemask);
@@ -41,4 +45,14 @@ void show_mem(unsigned int filter, nodemask_t *nodemask)
#ifdef CONFIG_MEMORY_FAILURE
printk("%lu pages hwpoisoned\n", atomic_long_read(&num_poisoned_pages));
#endif
+
+ pr_info("Unreclaimable slab info:\n");
+ dump_unreclaimable_slab(&buf);
+ printk("%s", buf.buf);
+ printbuf_reset(&buf);
+
+ printk("Shrinkers:\n");
+ shrinkers_to_text(&buf);
+ printk("%s", buf.buf);
+ printbuf_exit(&buf);
}
diff --git a/mm/slab.h b/mm/slab.h
index c7f2abc2b1..abefbf7674 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -788,10 +788,12 @@ static inline struct kmem_cache_node *get_node(struct kmem_cache *s, int node)

#endif

+struct printbuf;
+
#if defined(CONFIG_SLAB) || defined(CONFIG_SLUB_DEBUG)
-void dump_unreclaimable_slab(void);
+void dump_unreclaimable_slab(struct printbuf *);
#else
-static inline void dump_unreclaimable_slab(void)
+static inline void dump_unreclaimable_slab(struct printbuf *out)
{
}
#endif
diff --git a/mm/slab_common.c b/mm/slab_common.c
index 23f2ab0713..cb1c548c73 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -24,6 +24,7 @@
#include <asm/tlbflush.h>
#include <asm/page.h>
#include <linux/memcontrol.h>
+#include <linux/printbuf.h>

#define CREATE_TRACE_POINTS
#include <trace/events/kmem.h>
@@ -1084,10 +1085,15 @@ static int slab_show(struct seq_file *m, void *p)
return 0;
}

-void dump_unreclaimable_slab(void)
+void dump_unreclaimable_slab(struct printbuf *out)
{
struct kmem_cache *s;
struct slabinfo sinfo;
+ struct slab_by_mem {
+ struct kmem_cache *s;
+ size_t total, active;
+ } slabs_by_mem[10], n;
+ int i, nr = 0;

/*
* Here acquiring slab_mutex is risky since we don't prefer to get
@@ -1097,12 +1103,11 @@ 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_buf(out, "excessive unreclaimable slab but cannot dump stats\n");
return;
}

- pr_info("Unreclaimable slab info:\n");
- pr_info("Name Used Total\n");
+ buf->atomic++;

list_for_each_entry(s, &slab_caches, list) {
if (s->flags & SLAB_RECLAIM_ACCOUNT)
@@ -1110,11 +1115,43 @@ void dump_unreclaimable_slab(void)

get_slabinfo(s, &sinfo);

- if (sinfo.num_objs > 0)
- pr_info("%-17s %10luKB %10luKB\n", s->name,
- (sinfo.active_objs * s->size) / 1024,
- (sinfo.num_objs * s->size) / 1024);
+ if (!sinfo.num_objs)
+ continue;
+
+ n.s = s;
+ n.total = sinfo.num_objs * s->size;
+ n.active = sinfo.active_objs * s->size;
+
+ for (i = 0; i < nr; i++)
+ if (n.total < slabs_by_mem[i].total)
+ break;
+
+ if (nr < ARRAY_SIZE(slabs_by_mem)) {
+ memmove(&slabs_by_mem[i + 1],
+ &slabs_by_mem[i],
+ sizeof(slabs_by_mem[0]) * (nr - i));
+ nr++;
+ } else if (i) {
+ i--;
+ memmove(&slabs_by_mem[0],
+ &slabs_by_mem[1],
+ sizeof(slabs_by_mem[0]) * i);
+ } else {
+ continue;
+ }
+
+ slabs_by_mem[i] = n;
+ }
+
+ for (i = nr - 1; i >= 0; --i) {
+ pr_buf(out, "%-17s total: ", slabs_by_mem[i].s->name);
+ pr_human_readable_u64(out, slabs_by_mem[i].total);
+ pr_buf(out, " active: ");
+ pr_human_readable_u64(out, slabs_by_mem[i].active);
+ pr_newline(out);
}
+
+ --buf->atomic;
mutex_unlock(&slab_mutex);
}

--
2.35.2