From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751882AbdB0P1M (ORCPT ); Mon, 27 Feb 2017 10:27:12 -0500 Received: from mx2.suse.de ([195.135.220.15]:46816 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751251AbdB0P1L (ORCPT ); Mon, 27 Feb 2017 10:27:11 -0500 Date: Mon, 27 Feb 2017 16:25:17 +0100 From: Michal Hocko To: Tahsin Erdogan Cc: Tejun Heo , Christoph Lameter , Andrew Morton , Chris Wilson , Andrey Ryabinin , Roman Pen , Joonas Lahtinen , zijun_hu , Joonsoo Kim , David Rientjes , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 3/3] percpu: improve allocation success rate for non-GFP_KERNEL callers Message-ID: <20170227152516.GJ26504@dhcp22.suse.cz> References: <201702260805.zhem8KFI%fengguang.wu@intel.com> <20170226043829.14270-1-tahsin@google.com> <20170227095258.GG14029@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon 27-02-17 05:00:31, Tahsin Erdogan wrote: > On Mon, Feb 27, 2017 at 1:52 AM, Michal Hocko wrote: > > On Sat 25-02-17 20:38:29, Tahsin Erdogan wrote: > >> When pcpu_alloc() is called with gfp != GFP_KERNEL, the likelihood of > >> a failure is higher than GFP_KERNEL case. This is mainly because > >> pcpu_alloc() relies on previously allocated reserves and does not make > >> an effort to add memory to its pools for non-GFP_KERNEL case. > > > > Who is going to use a different mask? > > blkg_create() makes a call with a non-GFP_KERNEL mask: > new_blkg = blkg_alloc(blkcg, q, GFP_NOWAIT | __GFP_NOWARN); > > which turns into a call stack like below: > > __vmalloc+0x45/0x50 > pcpu_mem_zalloc+0x50/0x80 > pcpu_populate_chunk+0x3b/0x380 > pcpu_alloc+0x588/0x6e0 > __alloc_percpu_gfp+0xd/0x10 > __percpu_counter_init+0x55/0xc0 > blkg_alloc+0x76/0x230 > blkg_create+0x489/0x670 > blkg_lookup_create+0x9a/0x230 > generic_make_request_checks+0x7dd/0x890 > generic_make_request+0x1f/0x180 > submit_bio+0x61/0x120 OK, I see. Thanks for the clarification. I am not familiar with the pcp allocator much, but we have /* * No space left. Create a new chunk. We don't want multiple * tasks to create chunks simultaneously. Serialize and create iff * there's still no empty chunk after grabbing the mutex. */ if (is_atomic) goto fail; right before pcpu_populate_chunk so is this actually a problem? > > We already have __vmalloc_gfp, why this cannot be used? Also note that > > vmalloc dosn't really support arbitrary gfp flags. One have to be really > > careful because there are some internal allocations which are hardcoded > > GFP_KERNEL. Also this patch doesn't really add any new callers so it is > > hard to tell whether what you do actually makes sense and is correct. > > Did you mean to say __vmalloc? If so, yes, I should use that. yeah > By the way, I now noticed the might_sleep() in alloc_vmap_area() which makes > it unsafe to call vmalloc* in GFP_ATOMIC contexts. It was added recently: Do we call alloc_vmap_area from true atomic contexts (aka from under spinlocks etc)? I thought this was a nogo and GFP_NOWAIT resp. GFP_ATOMIC was more about optimistic request resp. access to memory reserves rather than true atomicity requirements. > commit 5803ed292e63 ("mm: mark all calls into the vmalloc subsystem as > potentially sleeping") > > Any suggestions on how to deal with that? For instance, would it be > safe to replace it with: > > might_sleep_if(gfpflags_allow_blocking(gfp_mask)); > > and then skip purge_vmap_area_lazy() if blocking is not allowed? -- Michal Hocko SUSE Labs