From mboxrd@z Thu Jan 1 00:00:00 1970 From: mina86@mina86.com (Michal Nazarewicz) Date: Sun, 01 Jan 2012 19:52:16 +0100 Subject: [PATCH 01/11] mm: page_alloc: set_migratetype_isolate: drain PCP prior to isolating In-Reply-To: References: <1325162352-24709-1-git-send-email-m.szyprowski@samsung.com> <1325162352-24709-2-git-send-email-m.szyprowski@samsung.com> Message-ID: To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Sun, 01 Jan 2012 17:06:53 +0100, Gilad Ben-Yossef wrote: > 2012/1/1 Michal Nazarewicz : >> Looks interesting, I'm not entirely sure why it does not end up a race >> condition, but in case of __zone_drain_all_pages() we already hold > If a page is in the PCP list when we check, you'll send the IPI and all is well. > > If it isn't when we check and gets added later you could just the same have > situation where we send the IPI, try to do try an empty PCP list and then > the page gets added. So we are not adding a race condition that is not there > already :-) Right, makes sense. >> zone->lock, so my fears are somehow gone.. I'll give it a try, and prepare >> a patch for __zone_drain_all_pages(). > I plan to send V5 of the IPI noise patch after some testing. It has a new > version of the drain_all_pages, with no allocation in the reclaim path > and no locking. You might want to wait till that one is out to base on it. This shouldn't be a problem for my case as set_migratetype_isolate() is hardly ever called in reclaim path. :) The change so far seems rather obvious: mm/page_alloc.c | 14 +++++++++++++- 1 files changed, 13 insertions(+), 1 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 424d36a..eaa686b 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -1181,7 +1181,19 @@ static void __zone_drain_local_pages(void *arg) */ static void __zone_drain_all_pages(struct zone *zone) { - on_each_cpu(__zone_drain_local_pages, zone, 1); + struct per_cpu_pageset *pcp; + cpumask_var_t cpus; + int cpu; + + if (likely(zalloc_cpumask_var(&cpus, GFP_ATOMIC | __GFP_NOWARN))) { + for_each_online_cpu(cpu) + if (per_cpu_ptr(zone->pageset, cpu)->pcp.count) + cpumask_set_cpu(cpu, cpus); + on_each_cpu_mask(cpus, __zone_drain_local_pages, zone, 1); + free_cpumask_var(cpus); + } else { + on_each_cpu(__zone_drain_local_pages, zone, 1); + } } #ifdef CONFIG_HIBERNATION -- Best regards, _ _ .o. | Liege of Serenely Enlightened Majesty of o' \,=./ `o ..o | Computer Science, Micha? ?mina86? Nazarewicz (o o) ooo +------------------ooO--(_)--Ooo--