On Thu, Jul 02, 2020 at 03:12:30PM +0800, Feng Tang wrote: > > <<<test_start>>> > > tag=overcommit_memory01 stime=1593425044 > > cmdline="overcommit_memory" > > contacts="" > > analysis=exit > > <<<test_output>>> > > tst_test.c:1247: INFO: Timeout per run is 0h 05m 00s > > overcommit_memory.c:116: INFO: MemTotal is 16394252 kB > > overcommit_memory.c:118: INFO: SwapTotal is 268435452 kB > > overcommit_memory.c:122: INFO: CommitLimit is 276632576 kB > > mem.c:817: INFO: set overcommit_ratio to 50 > > mem.c:817: INFO: set overcommit_memory to 2 > > overcommit_memory.c:187: INFO: malloc 551061440 kB failed > > overcommit_memory.c:208: PASS: alloc failed as expected > > overcommit_memory.c:183: INFO: malloc 276632576 kB successfully > > overcommit_memory.c:210: FAIL: alloc passed, expected to fail > > Thanks for the report! > > I took a rough look, and it all happens after changing the > overcommit policy from a looser one to OVERCOMMIT_NEVER. I suspect > it is due to the same cause as the previous warning message reported > by Qian Cai https://lore.kernel.org/lkml/20200526181459.GD991@xxxxxx/ > > Will further check it. I did reproduce the problem, and from the debugging, this should be the same root cause as https://lore.kernel.org/lkml/20200526181459.GD991@xxxxxx/ that loosing the batch cause some accuracy problem, and the solution of adding some sync is still needed, which is dicussed in First thing I tried a simple patch of using percpucounter_sum_read, and the problem can't be reproduced: --- a/mm/util.c +++ b/mm/util.c @@ -845,7 +845,7 @@ int __vm_enough_memory(struct mm_struct *mm, long pages, int cap_sys_admin) allowed -= min_t(long, mm->total_vm / 32, reserve); } - if (percpu_counter_read_positive(&vm_committed_as) < allowed) + if (percpu_counter_sum(&vm_committed_as) < allowed) return 0; error: vm_unacct_memory(pages); Then, I tried the sync patch we've discussed one month ago https://lore.kernel.org/lkml/20200529154315.GI93879@xxxxxxxxxxxxxxxxxxxxxxx/ with it, I run the case 200 times and the problem was not reproduced, can we consider taking this patch? Thanks, Feng diff --git a/include/linux/percpu_counter.h b/include/linux/percpu_counter.h index 0a4f54d..01861ee 100644 --- a/include/linux/percpu_counter.h +++ b/include/linux/percpu_counter.h @@ -44,6 +44,7 @@ void percpu_counter_add_batch(struct percpu_counter *fbc, s64 amount, s32 batch); s64 __percpu_counter_sum(struct percpu_counter *fbc); int __percpu_counter_compare(struct percpu_counter *fbc, s64 rhs, s32 batch); +void percpu_counter_sync(struct percpu_counter *fbc); static inline int percpu_counter_compare(struct percpu_counter *fbc, s64 rhs) { @@ -172,6 +173,9 @@ static inline bool percpu_counter_initialized(struct percpu_counter *fbc) return true; } +static inline void percpu_counter_sync(struct percpu_counter *fbc) +{ +} #endif /* CONFIG_SMP */ static inline void percpu_counter_inc(struct percpu_counter *fbc) diff --git a/lib/percpu_counter.c b/lib/percpu_counter.c index a66595b..d025137 100644 --- a/lib/percpu_counter.c +++ b/lib/percpu_counter.c @@ -98,6 +98,20 @@ void percpu_counter_add_batch(struct percpu_counter *fbc, s64 amount, s32 batch) } EXPORT_SYMBOL(percpu_counter_add_batch); +void percpu_counter_sync(struct percpu_counter *fbc) +{ + unsigned long flags; + s64 count; + + raw_spin_lock_irqsave(&fbc->lock, flags); + count = __this_cpu_read(*fbc->counters); + fbc->count += count; + __this_cpu_sub(*fbc->counters, count); + raw_spin_unlock_irqrestore(&fbc->lock, flags); +} +EXPORT_SYMBOL(percpu_counter_sync); + + /* * Add up all the per-cpu counts, return the result. This is a more accurate * but much slower version of percpu_counter_read_positive() diff --git a/mm/util.c b/mm/util.c index 98813da..8b9664e 100644 --- a/mm/util.c +++ b/mm/util.c @@ -746,14 +746,23 @@ int overcommit_ratio_handler(struct ctl_table *table, int write, void *buffer, return ret; } +static void sync_overcommit_as(struct work_struct *dummy) +{ + percpu_counter_sync(&vm_committed_as); +} + int overcommit_policy_handler(struct ctl_table *table, int write, void *buffer, size_t *lenp, loff_t *ppos) { int ret; ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos); - if (ret == 0 && write) + if (ret == 0 && write) { + if (sysctl_overcommit_memory == OVERCOMMIT_NEVER) + schedule_on_each_cpu(sync_overcommit_as); + mm_compute_batch(); + } pr_info("ocommit=%lld, real=%lld policy[%d] ratio=%d\n\n\n", percpu_counter_read_positive(&vm_committed_as),
