| Message ID | 20231122232515.177833-5-kent.overstreet@linux.dev (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | shrinker debugging improvements | expand |
On Wed 22-11-23 18:25:09, Kent Overstreet wrote: [...] > 00177 Shrinkers: > 00177 super_cache_scan: objects: 127 > 00177 super_cache_scan: objects: 106 > 00177 jbd2_journal_shrink_scan: objects: 32 > 00177 ext4_es_scan: objects: 32 > 00177 bch2_btree_cache_scan: objects: 8 > 00177 nr nodes: 24 > 00177 nr dirty: 0 > 00177 cannibalize lock: 0000000000000000 > 00177 > 00177 super_cache_scan: objects: 8 > 00177 super_cache_scan: objects: 1 It would be really great to provide an example on how these numbers are useful for the oom evaluation. [...] > @@ -423,4 +426,21 @@ void __show_mem(unsigned int filter, nodemask_t *nodemask, int max_zone_idx) > #ifdef CONFIG_MEMORY_FAILURE > printk("%lu pages hwpoisoned\n", atomic_long_read(&num_poisoned_pages)); > #endif > + > + buf = kmalloc(4096, GFP_ATOMIC); I really do not think we want to allow allocations from the OOM context. Is there any reason why this cannot be a statically allocated buffer? > + if (buf) { > + struct seq_buf s; > + > + printk("Unreclaimable slab info:\n"); > + seq_buf_init(&s, buf, 4096); > + dump_unreclaimable_slab(&s); > + printk("%s", seq_buf_str(&s)); > + > + printk("Shrinkers:\n"); > + seq_buf_init(&s, buf, 4096); > + shrinkers_to_text(&s); > + printk("%s", seq_buf_str(&s)); > + > + kfree(buf); > + } > }
On Tue, Nov 28, 2023 at 11:07:18AM +0100, Michal Hocko wrote: > On Wed 22-11-23 18:25:09, Kent Overstreet wrote: > [...] > > 00177 Shrinkers: > > 00177 super_cache_scan: objects: 127 > > 00177 super_cache_scan: objects: 106 > > 00177 jbd2_journal_shrink_scan: objects: 32 > > 00177 ext4_es_scan: objects: 32 > > 00177 bch2_btree_cache_scan: objects: 8 > > 00177 nr nodes: 24 > > 00177 nr dirty: 0 > > 00177 cannibalize lock: 0000000000000000 > > 00177 > > 00177 super_cache_scan: objects: 8 > > 00177 super_cache_scan: objects: 1 > > It would be really great to provide an example on how these numbers are > useful for the oom evaluation. I should've posted an example from the end of the patch series; I'll do that later today. > [...] > > @@ -423,4 +426,21 @@ void __show_mem(unsigned int filter, nodemask_t *nodemask, int max_zone_idx) > > #ifdef CONFIG_MEMORY_FAILURE > > printk("%lu pages hwpoisoned\n", atomic_long_read(&num_poisoned_pages)); > > #endif > > + > > + buf = kmalloc(4096, GFP_ATOMIC); > > I really do not think we want to allow allocations from the OOM context. > Is there any reason why this cannot be a statically allocated buffer? You've made this claim before without ever giving any reasoning behind it. It's GFP_ATOMIC; it has to work from _interrupt_ context, OOM context is fine. And no, we don't want to burn 4k on a static buffer that is almost never used; people do care about making the kernel run on small systems.
On Tue 28-11-23 12:54:39, Kent Overstreet wrote: > On Tue, Nov 28, 2023 at 11:07:18AM +0100, Michal Hocko wrote: [...] > > > @@ -423,4 +426,21 @@ void __show_mem(unsigned int filter, nodemask_t *nodemask, int max_zone_idx) > > > #ifdef CONFIG_MEMORY_FAILURE > > > printk("%lu pages hwpoisoned\n", atomic_long_read(&num_poisoned_pages)); > > > #endif > > > + > > > + buf = kmalloc(4096, GFP_ATOMIC); > > > > I really do not think we want to allow allocations from the OOM context. > > Is there any reason why this cannot be a statically allocated buffer? > > You've made this claim before without ever giving any reasoning behind > it. We are actively out of memory at the stage you would like to allocate memory. I am pretty sure I have mentioned this argument in the past. > It's GFP_ATOMIC; it has to work from _interrupt_ context, OOM context is > fine. This is a completely _different_ contexts. GFP_ATOMIC works around IRQ or any atomic context inability to wait for the reclaim by accessing the memory reserves. At the _global_ oom situation those reserves are extremely scarce resource. Debugging data is certainly not something we would want to compete with e.g. oom victims or their dependencies that might need to access those reserves in order to make a forward progress. Especially in case where the said debugging data is not detrimental to analyse the OOM situation. And to be completely honest, I haven't really seen any strong arguments for shrinker internal state dumping other than _in some very limited_ cases this _might_ be useful. > And no, we don't want to burn 4k on a static buffer that is almost never > used; people do care about making the kernel run on small systems. WE DO NOT ALLOCATE FROM OOM context, not to mention for something as disposable as debugging data which usefulness is not really clear. If there are systems which cannot effort a 4kb for static buffer then just disable this debugging data.
diff --git a/mm/oom_kill.c b/mm/oom_kill.c index 9e6071fde34a..4b825a2b353f 100644 --- a/mm/oom_kill.c +++ b/mm/oom_kill.c @@ -168,27 +168,6 @@ 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 @@ -462,8 +441,6 @@ static void dump_header(struct oom_control *oc) mem_cgroup_print_oom_meminfo(oc->memcg); else { __show_mem(SHOW_MEM_FILTER_NODES, oc->nodemask, gfp_zone(oc->gfp_mask)); - if (should_dump_unreclaim_slab()) - dump_unreclaimable_slab(); } if (sysctl_oom_dump_tasks) dump_tasks(oc); diff --git a/mm/show_mem.c b/mm/show_mem.c index ba0808d6917f..ab258ab1161c 100644 --- a/mm/show_mem.c +++ b/mm/show_mem.c @@ -12,10 +12,12 @@ #include <linux/hugetlb.h> #include <linux/mm.h> #include <linux/mmzone.h> +#include <linux/seq_buf.h> #include <linux/swap.h> #include <linux/vmstat.h> #include "internal.h" +#include "slab.h" #include "swap.h" atomic_long_t _totalram_pages __read_mostly; @@ -401,6 +403,7 @@ void __show_mem(unsigned int filter, nodemask_t *nodemask, int max_zone_idx) { unsigned long total = 0, reserved = 0, highmem = 0; struct zone *zone; + char *buf; printk("Mem-Info:\n"); show_free_areas(filter, nodemask, max_zone_idx); @@ -423,4 +426,21 @@ void __show_mem(unsigned int filter, nodemask_t *nodemask, int max_zone_idx) #ifdef CONFIG_MEMORY_FAILURE printk("%lu pages hwpoisoned\n", atomic_long_read(&num_poisoned_pages)); #endif + + buf = kmalloc(4096, GFP_ATOMIC); + if (buf) { + struct seq_buf s; + + printk("Unreclaimable slab info:\n"); + seq_buf_init(&s, buf, 4096); + dump_unreclaimable_slab(&s); + printk("%s", seq_buf_str(&s)); + + printk("Shrinkers:\n"); + seq_buf_init(&s, buf, 4096); + shrinkers_to_text(&s); + printk("%s", seq_buf_str(&s)); + + kfree(buf); + } } diff --git a/mm/slab.h b/mm/slab.h index 3d07fb428393..c16358a8424c 100644 --- a/mm/slab.h +++ b/mm/slab.h @@ -818,10 +818,12 @@ static inline struct kmem_cache_node *get_node(struct kmem_cache *s, int node) if ((__n = get_node(__s, __node))) +struct seq_buf; + #if defined(CONFIG_SLAB) || defined(CONFIG_SLUB_DEBUG) -void dump_unreclaimable_slab(void); +void dump_unreclaimable_slab(struct seq_buf *); #else -static inline void dump_unreclaimable_slab(void) +static inline void dump_unreclaimable_slab(struct seq_buf *out) { } #endif diff --git a/mm/slab_common.c b/mm/slab_common.c index 8d431193c273..1eadff512422 100644 --- a/mm/slab_common.c +++ b/mm/slab_common.c @@ -26,6 +26,7 @@ #include <asm/tlbflush.h> #include <asm/page.h> #include <linux/memcontrol.h> +#include <linux/seq_buf.h> #include <linux/stackdepot.h> #include "internal.h" @@ -1295,10 +1296,15 @@ static int slab_show(struct seq_file *m, void *p) return 0; } -void dump_unreclaimable_slab(void) +void dump_unreclaimable_slab(struct seq_buf *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 @@ -1308,24 +1314,52 @@ void dump_unreclaimable_slab(void) * without acquiring the mutex. */ if (!mutex_trylock(&slab_mutex)) { - pr_warn("excessive unreclaimable slab but cannot dump stats\n"); + seq_buf_puts(out, "excessive unreclaimable slab but cannot dump stats\n"); return; } - pr_info("Unreclaimable slab info:\n"); - pr_info("Name Used Total\n"); - list_for_each_entry(s, &slab_caches, list) { if (s->flags & SLAB_RECLAIM_ACCOUNT) continue; 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) { + seq_buf_printf(out, "%-17s total: ", slabs_by_mem[i].s->name); + seq_buf_human_readable_u64(out, slabs_by_mem[i].total, STRING_UNITS_2); + seq_buf_printf(out, " active: "); + seq_buf_human_readable_u64(out, slabs_by_mem[i].active, STRING_UNITS_2); + seq_buf_putc(out, '\n'); } + mutex_unlock(&slab_mutex); }
This patch: - 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(). Shrinkers need to be included in OOM/allocation failure reporting because they're responsible for memory reclaim - if a shrinker isn't giving up its memory, we need to know which one and why. More OOM reporting can be moved to show_mem.c and improved, this patch is only a start. New example output on OOM/memory allocation failure: 00177 Mem-Info: 00177 active_anon:13706 inactive_anon:32266 isolated_anon:16 00177 active_file:1653 inactive_file:1822 isolated_file:0 00177 unevictable:0 dirty:0 writeback:0 00177 slab_reclaimable:6242 slab_unreclaimable:11168 00177 mapped:3824 shmem:3 pagetables:1266 bounce:0 00177 kernel_misc_reclaimable:0 00177 free:4362 free_pcp:35 free_cma:0 00177 Node 0 active_anon:54824kB inactive_anon:129064kB active_file:6612kB inactive_file:7288kB unevictable:0kB isolated(anon):64kB isolated(file):0kB mapped:15296kB dirty:0kB writeback:0kB shmem:12kB writeback_tmp:0kB kernel_stack:3392kB pagetables:5064kB all_unreclaimable? no 00177 DMA free:2232kB boost:0kB min:88kB low:108kB high:128kB reserved_highatomic:0KB active_anon:2924kB inactive_anon:6596kB active_file:428kB inactive_file:384kB unevictable:0kB writepending:0kB present:15992kB managed:15360kB mlocked:0kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB 00177 lowmem_reserve[]: 0 426 426 426 00177 DMA32 free:15092kB boost:5836kB min:8432kB low:9080kB high:9728kB reserved_highatomic:0KB active_anon:52196kB inactive_anon:122392kB active_file:6176kB inactive_file:7068kB unevictable:0kB writepending:0kB present:507760kB managed:441816kB mlocked:0kB bounce:0kB free_pcp:72kB local_pcp:0kB free_cma:0kB 00177 lowmem_reserve[]: 0 0 0 0 00177 DMA: 284*4kB (UM) 53*8kB (UM) 21*16kB (U) 11*32kB (U) 0*64kB 0*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 2248kB 00177 DMA32: 2765*4kB (UME) 375*8kB (UME) 57*16kB (UM) 5*32kB (U) 0*64kB 0*128kB 0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 15132kB 00177 4656 total pagecache pages 00177 1031 pages in swap cache 00177 Swap cache stats: add 6572399, delete 6572173, find 488603/3286476 00177 Free swap = 509112kB 00177 Total swap = 2097148kB 00177 130938 pages RAM 00177 0 pages HighMem/MovableOnly 00177 16644 pages reserved 00177 Unreclaimable slab info: 00177 9p-fcall-cache total: 8.25 MiB active: 8.25 MiB 00177 kernfs_node_cache total: 2.15 MiB active: 2.15 MiB 00177 kmalloc-64 total: 2.08 MiB active: 2.07 MiB 00177 task_struct total: 1.95 MiB active: 1.95 MiB 00177 kmalloc-4k total: 1.50 MiB active: 1.50 MiB 00177 signal_cache total: 1.34 MiB active: 1.34 MiB 00177 kmalloc-2k total: 1.16 MiB active: 1.16 MiB 00177 bch_inode_info total: 1.02 MiB active: 922 KiB 00177 perf_event total: 1.02 MiB active: 1.02 MiB 00177 biovec-max total: 992 KiB active: 960 KiB 00177 Shrinkers: 00177 super_cache_scan: objects: 127 00177 super_cache_scan: objects: 106 00177 jbd2_journal_shrink_scan: objects: 32 00177 ext4_es_scan: objects: 32 00177 bch2_btree_cache_scan: objects: 8 00177 nr nodes: 24 00177 nr dirty: 0 00177 cannibalize lock: 0000000000000000 00177 00177 super_cache_scan: objects: 8 00177 super_cache_scan: objects: 1 Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Qi Zheng <zhengqi.arch@bytedance.com> Cc: Roman Gushchin <roman.gushchin@linux.dev> Cc: linux-mm@kvack.org Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev> --- mm/oom_kill.c | 23 --------------------- mm/show_mem.c | 20 +++++++++++++++++++ mm/slab.h | 6 ++++-- mm/slab_common.c | 52 +++++++++++++++++++++++++++++++++++++++--------- 4 files changed, 67 insertions(+), 34 deletions(-)