From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx203.postini.com [74.125.245.203]) by kanga.kvack.org (Postfix) with SMTP id 033DD6B00EE for ; Fri, 5 Apr 2013 08:27:16 -0400 (EDT) Message-ID: <515EC34C.8040704@parallels.com> Date: Fri, 5 Apr 2013 16:27:56 +0400 From: Glauber Costa MIME-Version: 1.0 Subject: Re: [PATCH 1/2] memcg: consistently use vmalloc for page_cgroup allocations References: <1365156072-24100-1-git-send-email-glommer@parallels.com> <1365156072-24100-2-git-send-email-glommer@parallels.com> <20130405120604.GN1953@cmpxchg.org> In-Reply-To: <20130405120604.GN1953@cmpxchg.org> Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Johannes Weiner Cc: cgroups@vger.kernel.org, linux-mm@kvack.org, kamezawa.hiroyu@jp.fujitsu.com, Michal Hocko On 04/05/2013 04:06 PM, Johannes Weiner wrote: > On Fri, Apr 05, 2013 at 02:01:11PM +0400, Glauber Costa wrote: >> Right now, allocation for page_cgroup is a bit complicated, dependent on >> a variety of system conditions: >> >> For flat memory, we are likely to need quite big pages, so the page >> allocator won't cut. We are forced to init flatmem mappings very early, >> because if we run after the page allocator is in place those allocations >> will be denied. Flatmem mappings thus resort to the bootmem allocator. >> >> We can fix this by using vmalloc for flatmem mappings. However, we now >> have the situation in which flatmem mapping allocate using vmalloc, but >> sparsemem may or may not allocate with vmalloc. It will try the >> page_allocator first, and retry vmalloc if it fails. > > Vmalloc space is a precious resource on 32-bit systems and harder on > the TLB than the identity mapping. > > It's a last resort thing for when you need an unusually large chunk of > contiguously addressable memory during runtime, like loading a module, > buffers shared with userspace etc.. But here we know, during boot > time, the exact amount of memory we need for the page_cgroup array. > > Code cleanup is not a good reason to use vmalloc in this case, IMO. > This is indeed a code cleanup, but a code cleanup with a side goal: freeing us from the need to register page_cgroup mandatorily at init time. This is done because page_cgroup_init_flatmem will use the bootmem allocator, to avoid the page allocator limitations. What I can try to do, and would happily do, is to try a normal page allocation and then resort to vmalloc if it is too big. Would that be okay to you ? -- 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