| Message ID | 20230426133919.1342942-2-yosryahmed@google.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | memcg: OOM log improvements | expand |
On Wed 26-04-23 13:39:18, Yosry Ahmed wrote: > Currently, we format all the memcg stats into a buffer in > mem_cgroup_print_oom_meminfo() and use pr_info() to dump it to the logs. > However, this buffer is large in size. Although it is currently working > as intended, ther is a dependency between the memcg stats buffer and the > printk record size limit. > > If we add more stats in the future and the buffer becomes larger than > the printk record size limit, or if the prink record size limit is > reduced, the logs may be truncated. > > It is safer to use seq_buf_do_printk(), which will automatically break > up the buffer at line breaks and issue small printk() calls. > > Refactor the code to move the seq_buf from memory_stat_format() to its > callers, and use seq_buf_do_printk() to print the seq_buf in > mem_cgroup_print_oom_meminfo(). > > Signed-off-by: Yosry Ahmed <yosryahmed@google.com> No objection from me but is it possible that more printk calls (one per line with this change correct?) would add a contention on the printk path? Acked-by: Michal Hocko <mhocko@suse.com> > --- > mm/memcontrol.c | 27 ++++++++++++++------------- > 1 file changed, 14 insertions(+), 13 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 5abffe6f8389..5922940f92c9 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -1551,13 +1551,10 @@ static inline unsigned long memcg_page_state_output(struct mem_cgroup *memcg, > return memcg_page_state(memcg, item) * memcg_page_state_unit(item); > } > > -static void memory_stat_format(struct mem_cgroup *memcg, char *buf, int bufsize) > +static void memory_stat_format(struct mem_cgroup *memcg, struct seq_buf *s) > { > - struct seq_buf s; > int i; > > - seq_buf_init(&s, buf, bufsize); > - > /* > * Provide statistics on the state of the memory subsystem as > * well as cumulative event counters that show past behavior. > @@ -1574,21 +1571,21 @@ static void memory_stat_format(struct mem_cgroup *memcg, char *buf, int bufsize) > u64 size; > > size = memcg_page_state_output(memcg, memory_stats[i].idx); > - seq_buf_printf(&s, "%s %llu\n", memory_stats[i].name, size); > + seq_buf_printf(s, "%s %llu\n", memory_stats[i].name, size); > > if (unlikely(memory_stats[i].idx == NR_SLAB_UNRECLAIMABLE_B)) { > size += memcg_page_state_output(memcg, > NR_SLAB_RECLAIMABLE_B); > - seq_buf_printf(&s, "slab %llu\n", size); > + seq_buf_printf(s, "slab %llu\n", size); > } > } > > /* Accumulated memory events */ > - seq_buf_printf(&s, "pgscan %lu\n", > + seq_buf_printf(s, "pgscan %lu\n", > memcg_events(memcg, PGSCAN_KSWAPD) + > memcg_events(memcg, PGSCAN_DIRECT) + > memcg_events(memcg, PGSCAN_KHUGEPAGED)); > - seq_buf_printf(&s, "pgsteal %lu\n", > + seq_buf_printf(s, "pgsteal %lu\n", > memcg_events(memcg, PGSTEAL_KSWAPD) + > memcg_events(memcg, PGSTEAL_DIRECT) + > memcg_events(memcg, PGSTEAL_KHUGEPAGED)); > @@ -1598,13 +1595,13 @@ static void memory_stat_format(struct mem_cgroup *memcg, char *buf, int bufsize) > memcg_vm_event_stat[i] == PGPGOUT) > continue; > > - seq_buf_printf(&s, "%s %lu\n", > + seq_buf_printf(s, "%s %lu\n", > vm_event_name(memcg_vm_event_stat[i]), > memcg_events(memcg, memcg_vm_event_stat[i])); > } > > /* The above should easily fit into one page */ > - WARN_ON_ONCE(seq_buf_has_overflowed(&s)); > + WARN_ON_ONCE(seq_buf_has_overflowed(s)); > } > > #define K(x) ((x) << (PAGE_SHIFT-10)) > @@ -1642,6 +1639,7 @@ void mem_cgroup_print_oom_meminfo(struct mem_cgroup *memcg) > { > /* Use static buffer, for the caller is holding oom_lock. */ > static char buf[PAGE_SIZE]; > + struct seq_buf s; > > lockdep_assert_held(&oom_lock); > > @@ -1664,8 +1662,9 @@ void mem_cgroup_print_oom_meminfo(struct mem_cgroup *memcg) > pr_info("Memory cgroup stats for "); > pr_cont_cgroup_path(memcg->css.cgroup); > pr_cont(":"); > - memory_stat_format(memcg, buf, sizeof(buf)); > - pr_info("%s", buf); > + seq_buf_init(&s, buf, sizeof(buf)); > + memory_stat_format(memcg, &s); > + seq_buf_do_printk(&s, KERN_INFO); > } > > /* > @@ -6573,10 +6572,12 @@ static int memory_stat_show(struct seq_file *m, void *v) > { > struct mem_cgroup *memcg = mem_cgroup_from_seq(m); > char *buf = kmalloc(PAGE_SIZE, GFP_KERNEL); > + struct seq_buf s; > > if (!buf) > return -ENOMEM; > - memory_stat_format(memcg, buf, PAGE_SIZE); > + seq_buf_init(&s, buf, PAGE_SIZE); > + memory_stat_format(memcg, &s); > seq_puts(m, buf); > kfree(buf); > return 0; > -- > 2.40.1.495.gc816e09b53d-goog
On (23/04/26 13:39), Yosry Ahmed wrote: > Currently, we format all the memcg stats into a buffer in > mem_cgroup_print_oom_meminfo() and use pr_info() to dump it to the logs. > However, this buffer is large in size. Although it is currently working > as intended, ther is a dependency between the memcg stats buffer and the > printk record size limit. > > If we add more stats in the future and the buffer becomes larger than > the printk record size limit, or if the prink record size limit is > reduced, the logs may be truncated. > > It is safer to use seq_buf_do_printk(), which will automatically break > up the buffer at line breaks and issue small printk() calls. > > Refactor the code to move the seq_buf from memory_stat_format() to its > callers, and use seq_buf_do_printk() to print the seq_buf in > mem_cgroup_print_oom_meminfo(). > > Signed-off-by: Yosry Ahmed <yosryahmed@google.com> FWIW, Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
On (23/04/26 17:24), Michal Hocko wrote: > No objection from me but is it possible that more printk calls (one per > line with this change correct?) would add a contention on the printk > path? It probably will have opposite effect: console->write of longer lines keep local IRQs disabled longer and keep console_waiter printk spinning (in console_trylock_spinning()) longer.
diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 5abffe6f8389..5922940f92c9 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -1551,13 +1551,10 @@ static inline unsigned long memcg_page_state_output(struct mem_cgroup *memcg, return memcg_page_state(memcg, item) * memcg_page_state_unit(item); } -static void memory_stat_format(struct mem_cgroup *memcg, char *buf, int bufsize) +static void memory_stat_format(struct mem_cgroup *memcg, struct seq_buf *s) { - struct seq_buf s; int i; - seq_buf_init(&s, buf, bufsize); - /* * Provide statistics on the state of the memory subsystem as * well as cumulative event counters that show past behavior. @@ -1574,21 +1571,21 @@ static void memory_stat_format(struct mem_cgroup *memcg, char *buf, int bufsize) u64 size; size = memcg_page_state_output(memcg, memory_stats[i].idx); - seq_buf_printf(&s, "%s %llu\n", memory_stats[i].name, size); + seq_buf_printf(s, "%s %llu\n", memory_stats[i].name, size); if (unlikely(memory_stats[i].idx == NR_SLAB_UNRECLAIMABLE_B)) { size += memcg_page_state_output(memcg, NR_SLAB_RECLAIMABLE_B); - seq_buf_printf(&s, "slab %llu\n", size); + seq_buf_printf(s, "slab %llu\n", size); } } /* Accumulated memory events */ - seq_buf_printf(&s, "pgscan %lu\n", + seq_buf_printf(s, "pgscan %lu\n", memcg_events(memcg, PGSCAN_KSWAPD) + memcg_events(memcg, PGSCAN_DIRECT) + memcg_events(memcg, PGSCAN_KHUGEPAGED)); - seq_buf_printf(&s, "pgsteal %lu\n", + seq_buf_printf(s, "pgsteal %lu\n", memcg_events(memcg, PGSTEAL_KSWAPD) + memcg_events(memcg, PGSTEAL_DIRECT) + memcg_events(memcg, PGSTEAL_KHUGEPAGED)); @@ -1598,13 +1595,13 @@ static void memory_stat_format(struct mem_cgroup *memcg, char *buf, int bufsize) memcg_vm_event_stat[i] == PGPGOUT) continue; - seq_buf_printf(&s, "%s %lu\n", + seq_buf_printf(s, "%s %lu\n", vm_event_name(memcg_vm_event_stat[i]), memcg_events(memcg, memcg_vm_event_stat[i])); } /* The above should easily fit into one page */ - WARN_ON_ONCE(seq_buf_has_overflowed(&s)); + WARN_ON_ONCE(seq_buf_has_overflowed(s)); } #define K(x) ((x) << (PAGE_SHIFT-10)) @@ -1642,6 +1639,7 @@ void mem_cgroup_print_oom_meminfo(struct mem_cgroup *memcg) { /* Use static buffer, for the caller is holding oom_lock. */ static char buf[PAGE_SIZE]; + struct seq_buf s; lockdep_assert_held(&oom_lock); @@ -1664,8 +1662,9 @@ void mem_cgroup_print_oom_meminfo(struct mem_cgroup *memcg) pr_info("Memory cgroup stats for "); pr_cont_cgroup_path(memcg->css.cgroup); pr_cont(":"); - memory_stat_format(memcg, buf, sizeof(buf)); - pr_info("%s", buf); + seq_buf_init(&s, buf, sizeof(buf)); + memory_stat_format(memcg, &s); + seq_buf_do_printk(&s, KERN_INFO); } /* @@ -6573,10 +6572,12 @@ static int memory_stat_show(struct seq_file *m, void *v) { struct mem_cgroup *memcg = mem_cgroup_from_seq(m); char *buf = kmalloc(PAGE_SIZE, GFP_KERNEL); + struct seq_buf s; if (!buf) return -ENOMEM; - memory_stat_format(memcg, buf, PAGE_SIZE); + seq_buf_init(&s, buf, PAGE_SIZE); + memory_stat_format(memcg, &s); seq_puts(m, buf); kfree(buf); return 0;
Currently, we format all the memcg stats into a buffer in mem_cgroup_print_oom_meminfo() and use pr_info() to dump it to the logs. However, this buffer is large in size. Although it is currently working as intended, ther is a dependency between the memcg stats buffer and the printk record size limit. If we add more stats in the future and the buffer becomes larger than the printk record size limit, or if the prink record size limit is reduced, the logs may be truncated. It is safer to use seq_buf_do_printk(), which will automatically break up the buffer at line breaks and issue small printk() calls. Refactor the code to move the seq_buf from memory_stat_format() to its callers, and use seq_buf_do_printk() to print the seq_buf in mem_cgroup_print_oom_meminfo(). Signed-off-by: Yosry Ahmed <yosryahmed@google.com> --- mm/memcontrol.c | 27 ++++++++++++++------------- 1 file changed, 14 insertions(+), 13 deletions(-)