From mboxrd@z Thu Jan 1 00:00:00 1970 From: Greg Thelen Subject: [PATCH] memcg: make mem_cgroup_read_stat() unsigned Date: Tue, 22 Sep 2015 15:16:32 -0700 Message-ID: <1442960192-83405-1-git-send-email-gthelen@google.com> Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20120113; h=from:to:cc:subject:date:message-id; bh=F35BEPUk9ApJ72yaxgAeslu4nHjdaS3GS8+efaCm2zg=; b=QhwR9J93sokRcMp7bwr9DuYU1Bg/slCzK6E120eElgmBHChPW4b8K4YIteXu4Hgs3m 9doAX7pGaxiIWVw6HiJfJzhR5RIP6MRl7oEEIF/6kwo5k++DcseGZtue+/4FkFxy1kkl aTkC8n2yVM1Oo2jhk+lyBmAfnBz53gMQXTGDsKDPkyPOtZIjpUfbYls65gjeLSIB+dEJ yzFKUtDuZZ1h2qaxntTii+0goF/TFFlYmmSpP+xIX3Wnx7sfPwySA0CFJV2CeTdvlE1b mI5SCJ718NJciAKxcCd1ynkPkZsxdVi4d3Od4uppGuZQhKMug5ye4w/TCq6V5NA2Hrdm EZ7A== Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Andrew Morton , Johannes Weiner , Michal Hocko Cc: cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Greg Thelen mem_cgroup_read_stat() returns a page count by summing per cpu page counters. The summing is racy wrt. updates, so a transient negative sum is possible. Callers don't want negative values: - mem_cgroup_wb_stats() doesn't want negative nr_dirty or nr_writeback. - oom reports and memory.stat shouldn't show confusing negative usage. - tree_usage() already avoids negatives. Avoid returning negative page counts from mem_cgroup_read_stat() and convert it to unsigned. Signed-off-by: Greg Thelen --- mm/memcontrol.c | 30 ++++++++++++++++++------------ 1 file changed, 18 insertions(+), 12 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 6ddaeba34e09..2633e9be4a99 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -644,12 +644,14 @@ mem_cgroup_largest_soft_limit_node(struct mem_cgroup_tree_per_zone *mctz) } /* + * Return page count for single (non recursive) @memcg. + * * Implementation Note: reading percpu statistics for memcg. * * Both of vmstat[] and percpu_counter has threshold and do periodic * synchronization to implement "quick" read. There are trade-off between * reading cost and precision of value. Then, we may have a chance to implement - * a periodic synchronizion of counter in memcg's counter. + * a periodic synchronization of counter in memcg's counter. * * But this _read() function is used for user interface now. The user accounts * memory usage by memory cgroup and he _always_ requires exact value because @@ -659,17 +661,24 @@ mem_cgroup_largest_soft_limit_node(struct mem_cgroup_tree_per_zone *mctz) * * If there are kernel internal actions which can make use of some not-exact * value, and reading all cpu value can be performance bottleneck in some - * common workload, threashold and synchonization as vmstat[] should be + * common workload, threashold and synchronization as vmstat[] should be * implemented. */ -static long mem_cgroup_read_stat(struct mem_cgroup *memcg, - enum mem_cgroup_stat_index idx) +static unsigned long +mem_cgroup_read_stat(struct mem_cgroup *memcg, enum mem_cgroup_stat_index idx) { long val = 0; int cpu; + /* Per-cpu values can be negative, use a signed accumulator */ for_each_possible_cpu(cpu) val += per_cpu(memcg->stat->count[idx], cpu); + /* + * Summing races with updates, so val may be negative. Avoid exposing + * transient negative values. + */ + if (val < 0) + val = 0; return val; } @@ -1254,7 +1263,7 @@ void mem_cgroup_print_oom_info(struct mem_cgroup *memcg, struct task_struct *p) for (i = 0; i < MEM_CGROUP_STAT_NSTATS; i++) { if (i == MEM_CGROUP_STAT_SWAP && !do_swap_account) continue; - pr_cont(" %s:%ldKB", mem_cgroup_stat_names[i], + pr_cont(" %s:%luKB", mem_cgroup_stat_names[i], K(mem_cgroup_read_stat(iter, i))); } @@ -2819,14 +2828,11 @@ static unsigned long tree_stat(struct mem_cgroup *memcg, enum mem_cgroup_stat_index idx) { struct mem_cgroup *iter; - long val = 0; + unsigned long val = 0; - /* Per-cpu values can be negative, use a signed accumulator */ for_each_mem_cgroup_tree(iter, memcg) val += mem_cgroup_read_stat(iter, idx); - if (val < 0) /* race ? */ - val = 0; return val; } @@ -3169,7 +3175,7 @@ static int memcg_stat_show(struct seq_file *m, void *v) for (i = 0; i < MEM_CGROUP_STAT_NSTATS; i++) { if (i == MEM_CGROUP_STAT_SWAP && !do_swap_account) continue; - seq_printf(m, "%s %ld\n", mem_cgroup_stat_names[i], + seq_printf(m, "%s %lu\n", mem_cgroup_stat_names[i], mem_cgroup_read_stat(memcg, i) * PAGE_SIZE); } @@ -3194,13 +3200,13 @@ static int memcg_stat_show(struct seq_file *m, void *v) (u64)memsw * PAGE_SIZE); for (i = 0; i < MEM_CGROUP_STAT_NSTATS; i++) { - long long val = 0; + unsigned long long val = 0; if (i == MEM_CGROUP_STAT_SWAP && !do_swap_account) continue; for_each_mem_cgroup_tree(mi, memcg) val += mem_cgroup_read_stat(mi, i) * PAGE_SIZE; - seq_printf(m, "total_%s %lld\n", mem_cgroup_stat_names[i], val); + seq_printf(m, "total_%s %llu\n", mem_cgroup_stat_names[i], val); } for (i = 0; i < MEM_CGROUP_EVENTS_NSTATS; i++) { -- 2.6.0.rc0.131.gf624c3d From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pa0-f44.google.com (mail-pa0-f44.google.com [209.85.220.44]) by kanga.kvack.org (Postfix) with ESMTP id 52C416B0253 for ; Tue, 22 Sep 2015 18:16:38 -0400 (EDT) Received: by pacbt3 with SMTP id bt3so2619861pac.3 for ; Tue, 22 Sep 2015 15:16:38 -0700 (PDT) Received: from mail-pa0-x231.google.com (mail-pa0-x231.google.com. [2607:f8b0:400e:c03::231]) by mx.google.com with ESMTPS id w7si5615212pbs.85.2015.09.22.15.16.37 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 22 Sep 2015 15:16:37 -0700 (PDT) Received: by pacfv12 with SMTP id fv12so21180156pac.2 for ; Tue, 22 Sep 2015 15:16:37 -0700 (PDT) From: Greg Thelen Subject: [PATCH] memcg: make mem_cgroup_read_stat() unsigned Date: Tue, 22 Sep 2015 15:16:32 -0700 Message-Id: <1442960192-83405-1-git-send-email-gthelen@google.com> Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton , Johannes Weiner , Michal Hocko Cc: cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Greg Thelen mem_cgroup_read_stat() returns a page count by summing per cpu page counters. The summing is racy wrt. updates, so a transient negative sum is possible. Callers don't want negative values: - mem_cgroup_wb_stats() doesn't want negative nr_dirty or nr_writeback. - oom reports and memory.stat shouldn't show confusing negative usage. - tree_usage() already avoids negatives. Avoid returning negative page counts from mem_cgroup_read_stat() and convert it to unsigned. Signed-off-by: Greg Thelen --- mm/memcontrol.c | 30 ++++++++++++++++++------------ 1 file changed, 18 insertions(+), 12 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 6ddaeba34e09..2633e9be4a99 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -644,12 +644,14 @@ mem_cgroup_largest_soft_limit_node(struct mem_cgroup_tree_per_zone *mctz) } /* + * Return page count for single (non recursive) @memcg. + * * Implementation Note: reading percpu statistics for memcg. * * Both of vmstat[] and percpu_counter has threshold and do periodic * synchronization to implement "quick" read. There are trade-off between * reading cost and precision of value. Then, we may have a chance to implement - * a periodic synchronizion of counter in memcg's counter. + * a periodic synchronization of counter in memcg's counter. * * But this _read() function is used for user interface now. The user accounts * memory usage by memory cgroup and he _always_ requires exact value because @@ -659,17 +661,24 @@ mem_cgroup_largest_soft_limit_node(struct mem_cgroup_tree_per_zone *mctz) * * If there are kernel internal actions which can make use of some not-exact * value, and reading all cpu value can be performance bottleneck in some - * common workload, threashold and synchonization as vmstat[] should be + * common workload, threashold and synchronization as vmstat[] should be * implemented. */ -static long mem_cgroup_read_stat(struct mem_cgroup *memcg, - enum mem_cgroup_stat_index idx) +static unsigned long +mem_cgroup_read_stat(struct mem_cgroup *memcg, enum mem_cgroup_stat_index idx) { long val = 0; int cpu; + /* Per-cpu values can be negative, use a signed accumulator */ for_each_possible_cpu(cpu) val += per_cpu(memcg->stat->count[idx], cpu); + /* + * Summing races with updates, so val may be negative. Avoid exposing + * transient negative values. + */ + if (val < 0) + val = 0; return val; } @@ -1254,7 +1263,7 @@ void mem_cgroup_print_oom_info(struct mem_cgroup *memcg, struct task_struct *p) for (i = 0; i < MEM_CGROUP_STAT_NSTATS; i++) { if (i == MEM_CGROUP_STAT_SWAP && !do_swap_account) continue; - pr_cont(" %s:%ldKB", mem_cgroup_stat_names[i], + pr_cont(" %s:%luKB", mem_cgroup_stat_names[i], K(mem_cgroup_read_stat(iter, i))); } @@ -2819,14 +2828,11 @@ static unsigned long tree_stat(struct mem_cgroup *memcg, enum mem_cgroup_stat_index idx) { struct mem_cgroup *iter; - long val = 0; + unsigned long val = 0; - /* Per-cpu values can be negative, use a signed accumulator */ for_each_mem_cgroup_tree(iter, memcg) val += mem_cgroup_read_stat(iter, idx); - if (val < 0) /* race ? */ - val = 0; return val; } @@ -3169,7 +3175,7 @@ static int memcg_stat_show(struct seq_file *m, void *v) for (i = 0; i < MEM_CGROUP_STAT_NSTATS; i++) { if (i == MEM_CGROUP_STAT_SWAP && !do_swap_account) continue; - seq_printf(m, "%s %ld\n", mem_cgroup_stat_names[i], + seq_printf(m, "%s %lu\n", mem_cgroup_stat_names[i], mem_cgroup_read_stat(memcg, i) * PAGE_SIZE); } @@ -3194,13 +3200,13 @@ static int memcg_stat_show(struct seq_file *m, void *v) (u64)memsw * PAGE_SIZE); for (i = 0; i < MEM_CGROUP_STAT_NSTATS; i++) { - long long val = 0; + unsigned long long val = 0; if (i == MEM_CGROUP_STAT_SWAP && !do_swap_account) continue; for_each_mem_cgroup_tree(mi, memcg) val += mem_cgroup_read_stat(mi, i) * PAGE_SIZE; - seq_printf(m, "total_%s %lld\n", mem_cgroup_stat_names[i], val); + seq_printf(m, "total_%s %llu\n", mem_cgroup_stat_names[i], val); } for (i = 0; i < MEM_CGROUP_EVENTS_NSTATS; i++) { -- 2.6.0.rc0.131.gf624c3d -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759772AbbIVWQk (ORCPT ); Tue, 22 Sep 2015 18:16:40 -0400 Received: from mail-pa0-f52.google.com ([209.85.220.52]:33536 "EHLO mail-pa0-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759514AbbIVWQh (ORCPT ); Tue, 22 Sep 2015 18:16:37 -0400 From: Greg Thelen To: Andrew Morton , Johannes Weiner , Michal Hocko Cc: cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Greg Thelen Subject: [PATCH] memcg: make mem_cgroup_read_stat() unsigned Date: Tue, 22 Sep 2015 15:16:32 -0700 Message-Id: <1442960192-83405-1-git-send-email-gthelen@google.com> X-Mailer: git-send-email 2.6.0.rc0.131.gf624c3d Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org mem_cgroup_read_stat() returns a page count by summing per cpu page counters. The summing is racy wrt. updates, so a transient negative sum is possible. Callers don't want negative values: - mem_cgroup_wb_stats() doesn't want negative nr_dirty or nr_writeback. - oom reports and memory.stat shouldn't show confusing negative usage. - tree_usage() already avoids negatives. Avoid returning negative page counts from mem_cgroup_read_stat() and convert it to unsigned. Signed-off-by: Greg Thelen --- mm/memcontrol.c | 30 ++++++++++++++++++------------ 1 file changed, 18 insertions(+), 12 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 6ddaeba34e09..2633e9be4a99 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -644,12 +644,14 @@ mem_cgroup_largest_soft_limit_node(struct mem_cgroup_tree_per_zone *mctz) } /* + * Return page count for single (non recursive) @memcg. + * * Implementation Note: reading percpu statistics for memcg. * * Both of vmstat[] and percpu_counter has threshold and do periodic * synchronization to implement "quick" read. There are trade-off between * reading cost and precision of value. Then, we may have a chance to implement - * a periodic synchronizion of counter in memcg's counter. + * a periodic synchronization of counter in memcg's counter. * * But this _read() function is used for user interface now. The user accounts * memory usage by memory cgroup and he _always_ requires exact value because @@ -659,17 +661,24 @@ mem_cgroup_largest_soft_limit_node(struct mem_cgroup_tree_per_zone *mctz) * * If there are kernel internal actions which can make use of some not-exact * value, and reading all cpu value can be performance bottleneck in some - * common workload, threashold and synchonization as vmstat[] should be + * common workload, threashold and synchronization as vmstat[] should be * implemented. */ -static long mem_cgroup_read_stat(struct mem_cgroup *memcg, - enum mem_cgroup_stat_index idx) +static unsigned long +mem_cgroup_read_stat(struct mem_cgroup *memcg, enum mem_cgroup_stat_index idx) { long val = 0; int cpu; + /* Per-cpu values can be negative, use a signed accumulator */ for_each_possible_cpu(cpu) val += per_cpu(memcg->stat->count[idx], cpu); + /* + * Summing races with updates, so val may be negative. Avoid exposing + * transient negative values. + */ + if (val < 0) + val = 0; return val; } @@ -1254,7 +1263,7 @@ void mem_cgroup_print_oom_info(struct mem_cgroup *memcg, struct task_struct *p) for (i = 0; i < MEM_CGROUP_STAT_NSTATS; i++) { if (i == MEM_CGROUP_STAT_SWAP && !do_swap_account) continue; - pr_cont(" %s:%ldKB", mem_cgroup_stat_names[i], + pr_cont(" %s:%luKB", mem_cgroup_stat_names[i], K(mem_cgroup_read_stat(iter, i))); } @@ -2819,14 +2828,11 @@ static unsigned long tree_stat(struct mem_cgroup *memcg, enum mem_cgroup_stat_index idx) { struct mem_cgroup *iter; - long val = 0; + unsigned long val = 0; - /* Per-cpu values can be negative, use a signed accumulator */ for_each_mem_cgroup_tree(iter, memcg) val += mem_cgroup_read_stat(iter, idx); - if (val < 0) /* race ? */ - val = 0; return val; } @@ -3169,7 +3175,7 @@ static int memcg_stat_show(struct seq_file *m, void *v) for (i = 0; i < MEM_CGROUP_STAT_NSTATS; i++) { if (i == MEM_CGROUP_STAT_SWAP && !do_swap_account) continue; - seq_printf(m, "%s %ld\n", mem_cgroup_stat_names[i], + seq_printf(m, "%s %lu\n", mem_cgroup_stat_names[i], mem_cgroup_read_stat(memcg, i) * PAGE_SIZE); } @@ -3194,13 +3200,13 @@ static int memcg_stat_show(struct seq_file *m, void *v) (u64)memsw * PAGE_SIZE); for (i = 0; i < MEM_CGROUP_STAT_NSTATS; i++) { - long long val = 0; + unsigned long long val = 0; if (i == MEM_CGROUP_STAT_SWAP && !do_swap_account) continue; for_each_mem_cgroup_tree(mi, memcg) val += mem_cgroup_read_stat(mi, i) * PAGE_SIZE; - seq_printf(m, "total_%s %lld\n", mem_cgroup_stat_names[i], val); + seq_printf(m, "total_%s %llu\n", mem_cgroup_stat_names[i], val); } for (i = 0; i < MEM_CGROUP_EVENTS_NSTATS; i++) { -- 2.6.0.rc0.131.gf624c3d