From patchwork Thu Sep 29 11:07:14 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Chris Wilson X-Patchwork-Id: 9356341 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id A707D6077B for ; Thu, 29 Sep 2016 11:09:21 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 97D48298F2 for ; Thu, 29 Sep 2016 11:09:21 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 8B9F929954; Thu, 29 Sep 2016 11:09:21 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-4.2 required=2.0 tests=BAYES_00, RCVD_IN_DNSWL_MED autolearn=unavailable version=3.3.1 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.9]) (using TLSv1.2 with cipher AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id C4007298F2 for ; Thu, 29 Sep 2016 11:09:16 +0000 (UTC) Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.85_2 #1 (Red Hat Linux)) id 1bpZBs-0001VW-5c; Thu, 29 Sep 2016 11:07:48 +0000 Received: from mail.fireflyinternet.com ([109.228.58.192] helo=fireflyinternet.com) by bombadil.infradead.org with esmtps (Exim 4.85_2 #1 (Red Hat Linux)) id 1bpZBn-0001P9-6D for linux-arm-kernel@lists.infradead.org; Thu, 29 Sep 2016 11:07:44 +0000 X-Default-Received-SPF: pass (skip=forwardok (res=PASS)) x-ip-name=78.156.65.138; Received: from nuc-i3427.alporthouse.com (unverified [78.156.65.138]) by fireflyinternet.com (Firefly Internet (M1)) with ESMTP id 2439424-1500050 for multiple; Thu, 29 Sep 2016 12:07:15 +0100 Received: by nuc-i3427.alporthouse.com (sSMTP sendmail emulation); Thu, 29 Sep 2016 12:07:14 +0100 Date: Thu, 29 Sep 2016 12:07:14 +0100 From: Chris Wilson To: Jisheng Zhang 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-Disposition: inline In-Reply-To: <20160929162808.745c869b@xhacker> User-Agent: Mutt/1.5.21 (2010-09-15) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20160929_040743_599397_F1AE11EF X-CRM114-Status: GOOD ( 21.36 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.20 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, agnel.joel@gmail.com, rientjes@google.com, akpm@linux-foundation.org, mgorman@techsingularity.net, iamjoonsoo.kim@lge.com, linux-arm-kernel@lists.infradead.org Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org X-Virus-Scanned: ClamAV using ClamSMTP 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 ? -Chris 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); } }