From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f72.google.com (mail-wm0-f72.google.com [74.125.82.72]) by kanga.kvack.org (Postfix) with ESMTP id 5C2376B029E for ; Thu, 29 Sep 2016 07:07:55 -0400 (EDT) Received: by mail-wm0-f72.google.com with SMTP id w84so70021023wmg.1 for ; Thu, 29 Sep 2016 04:07:55 -0700 (PDT) Received: from fireflyinternet.com (mail.fireflyinternet.com. [109.228.58.192]) by mx.google.com with ESMTPS id r4si13601253wmd.5.2016.09.29.04.07.53 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 29 Sep 2016 04:07:53 -0700 (PDT) Date: Thu, 29 Sep 2016 12:07:14 +0100 From: Chris Wilson Subject: Re: [PATCH] mm/vmalloc: reduce the number of lazy_max_pages to reduce latency Message-ID: <20160929110714.GF28107@nuc-i3427.alporthouse.com> References: <20160929073411.3154-1-jszhang@marvell.com> <20160929081818.GE28107@nuc-i3427.alporthouse.com> <20160929162808.745c869b@xhacker> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160929162808.745c869b@xhacker> Sender: owner-linux-mm@kvack.org List-ID: To: Jisheng Zhang Cc: akpm@linux-foundation.org, mgorman@techsingularity.net, rientjes@google.com, iamjoonsoo.kim@lge.com, agnel.joel@gmail.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org On Thu, Sep 29, 2016 at 04:28:08PM +0800, Jisheng Zhang wrote: > On Thu, 29 Sep 2016 09:18:18 +0100 Chris Wilson wrote: > > > On Thu, Sep 29, 2016 at 03:34:11PM +0800, Jisheng Zhang wrote: > > > On Marvell berlin arm64 platforms, I see the preemptoff tracer report > > > a max 26543 us latency at __purge_vmap_area_lazy, this latency is an > > > awfully bad for STB. And the ftrace log also shows __free_vmap_area > > > contributes most latency now. I noticed that Joel mentioned the same > > > issue[1] on x86 platform and gave two solutions, but it seems no patch > > > is sent out for this purpose. > > > > > > This patch adopts Joel's first solution, but I use 16MB per core > > > rather than 8MB per core for the number of lazy_max_pages. After this > > > patch, the preemptoff tracer reports a max 6455us latency, reduced to > > > 1/4 of original result. > > > > My understanding is that > > > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > > index 91f44e78c516..3f7c6d6969ac 100644 > > --- a/mm/vmalloc.c > > +++ b/mm/vmalloc.c > > @@ -626,7 +626,6 @@ void set_iounmap_nonlazy(void) > > static void __purge_vmap_area_lazy(unsigned long *start, unsigned long *end, > > int sync, int force_flush) > > { > > - static DEFINE_SPINLOCK(purge_lock); > > struct llist_node *valist; > > struct vmap_area *va; > > struct vmap_area *n_va; > > @@ -637,12 +636,6 @@ static void __purge_vmap_area_lazy(unsigned long *start, unsigned long *end, > > * should not expect such behaviour. This just simplifies locking for > > * the case that isn't actually used at the moment anyway. > > */ > > - if (!sync && !force_flush) { > > - if (!spin_trylock(&purge_lock)) > > - return; > > - } else > > - spin_lock(&purge_lock); > > - > > if (sync) > > purge_fragmented_blocks_allcpus(); > > > > @@ -667,7 +660,6 @@ static void __purge_vmap_area_lazy(unsigned long *start, unsigned long *end, > > __free_vmap_area(va); > > spin_unlock(&vmap_area_lock); > > Hi Chris, > > Per my test, the bottleneck now is __free_vmap_area() over the valist, the > iteration is protected with spinlock vmap_area_lock. So the larger lazy max > pages, the longer valist, the bigger the latency. > > So besides above patch, we still need to remove vmap_are_lock or replace with > mutex. Or follow up with diff --git a/mm/vmalloc.c b/mm/vmalloc.c index 3f7c6d6969ac..67b5475f0b0a 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -656,8 +656,10 @@ static void __purge_vmap_area_lazy(unsigned long *start, unsigned long *end, if (nr) { spin_lock(&vmap_area_lock); - llist_for_each_entry_safe(va, n_va, valist, purge_list) + llist_for_each_entry_safe(va, n_va, valist, purge_list) { __free_vmap_area(va); + cond_resched_lock(&vmap_area_lock); + } spin_unlock(&vmap_area_lock); } } ? -Chris -- Chris Wilson, Intel Open Source Technology Centre -- 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