From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gilad Ben-Yossef Subject: [PATCH v5 7/8] mm: Only IPI CPUs to drain local pages if they exist Date: Mon, 2 Jan 2012 12:24:18 +0200 Message-ID: <1325499859-2262-8-git-send-email-gilad@benyossef.com> References: <1325499859-2262-1-git-send-email-gilad@benyossef.com> Cc: Gilad Ben-Yossef , Chris Metcalf , Peter Zijlstra , Frederic Weisbecker , Russell King , linux-mm@kvack.org, Pekka Enberg , Matt Mackall , Sasha Levin , Rik van Riel , Andi Kleen , Mel Gorman , Andrew Morton , Alexander Viro , linux-fsdevel@vger.kernel.org, Avi Kivity To: linux-kernel@vger.kernel.org Return-path: In-Reply-To: <1325499859-2262-1-git-send-email-gilad@benyossef.com> Sender: owner-linux-mm@kvack.org List-Id: linux-fsdevel.vger.kernel.org Calculate a cpumask of CPUs with per-cpu pages in any zone and only send an IPI requesting CPUs to drain these pages to the buddy allocator if they actually have pages when asked to flush. This patch saves 99% of IPIs asking to drain per-cpu pages in case of severe memory preassure that leads to OOM since in these cases multiple, possibly concurrent, allocation requests end up in the direct reclaim code path so when the per-cpu pages end up reclaimed on first allocation failure for most of the proceeding allocation attempts until the memory pressure is off (possibly via the OOM killer) there are no per-cpu pages on most CPUs (and there can easily be hundreds of them). This also has the side effect of shortening the average latency of direct reclaim by 1 or more order of magnitude since waiting for all the CPUs to ACK the IPI takes a long time. Tested by running "hackbench 400" on a 4 CPU x86 otherwise idle VM and observing the difference between the number of direct reclaim attempts that end up in drain_all_pages() and those were more then 1/2 of the online CPU had any per-cpu page in them, using the vmstat counters introduced in the next patch in the series and using proc/interrupts. In the test sceanrio, this saved around 500 global IPIs. After trigerring an OOM: $ cat /proc/vmstat ... pcp_global_drain 627 pcp_global_ipi_saved 578 I've also seen the number of drains reach 15k calls with the saved percentage reaching 99% when there are more tasks running during an OOM kill. Signed-off-by: Gilad Ben-Yossef Acked-by: Christoph Lameter CC: Chris Metcalf CC: Peter Zijlstra CC: Frederic Weisbecker CC: Russell King CC: linux-mm@kvack.org CC: Pekka Enberg CC: Matt Mackall CC: Sasha Levin CC: Rik van Riel CC: Andi Kleen CC: Mel Gorman CC: Andrew Morton CC: Alexander Viro CC: linux-fsdevel@vger.kernel.org CC: Avi Kivity --- Christopth Ack was for a previous version that allocated the cpumask in drain_all_pages(). mm/page_alloc.c | 26 +++++++++++++++++++++++++- 1 files changed, 25 insertions(+), 1 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 2b8ba3a..092c331 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -67,6 +67,14 @@ DEFINE_PER_CPU(int, numa_node); EXPORT_PER_CPU_SYMBOL(numa_node); #endif +/* + * A global cpumask of CPUs with per-cpu pages that gets + * recomputed on each drain. We use a global cpumask + * for to avoid allocation on direct reclaim code path + * for CONFIG_CPUMASK_OFFSTACK=y + */ +static cpumask_var_t cpus_with_pcps; + #ifdef CONFIG_HAVE_MEMORYLESS_NODES /* * N.B., Do NOT reference the '_numa_mem_' per cpu variable directly. @@ -1119,7 +1127,19 @@ void drain_local_pages(void *arg) */ void drain_all_pages(void) { - on_each_cpu(drain_local_pages, NULL, 1); + int cpu; + struct per_cpu_pageset *pcp; + struct zone *zone; + + for_each_online_cpu(cpu) + for_each_populated_zone(zone) { + pcp = per_cpu_ptr(zone->pageset, cpu); + if (pcp->pcp.count) + cpumask_set_cpu(cpu, cpus_with_pcps); + else + cpumask_clear_cpu(cpu, cpus_with_pcps); + } + on_each_cpu_mask(cpus_with_pcps, drain_local_pages, NULL, 1); } #ifdef CONFIG_HIBERNATION @@ -3623,6 +3643,10 @@ static void setup_zone_pageset(struct zone *zone) void __init setup_per_cpu_pageset(void) { struct zone *zone; + int ret; + + ret = zalloc_cpumask_var(&cpus_with_pcps, GFP_KERNEL); + BUG_ON(!ret); for_each_populated_zone(zone) setup_zone_pageset(zone); -- 1.7.0.4 -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org