From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kamezawa Hiroyuki Subject: Re: [PATCH 1/2] memcg: consistently use vmalloc for page_cgroup allocations Date: Tue, 09 Apr 2013 11:41:59 +0900 Message-ID: <51637FF7.4070101@jp.fujitsu.com> References: <1365156072-24100-1-git-send-email-glommer@parallels.com> <1365156072-24100-2-git-send-email-glommer@parallels.com> <20130405120604.GN1953@cmpxchg.org> <515EC34C.8040704@parallels.com> <20130405162536.GO1953@cmpxchg.org> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20130405162536.GO1953-druUgvl0LCNAfugRpC6u6w@public.gmane.org> Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii"; format="flowed" To: Johannes Weiner Cc: Glauber Costa , cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, Michal Hocko (2013/04/06 1:25), Johannes Weiner wrote: > On Fri, Apr 05, 2013 at 04:27:56PM +0400, Glauber Costa wrote: >> 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 ? > > With the size of page_cgroup right now (2 words), we need half a page > per MB of represented memory on 32 bit, so booting on a 4GB 32 bit > machine needs an order-11 (MAX_ORDER) allocation and thus fall back to > 8MB of the 128MB vmalloc space. A 16GB machine falls back to 32MB, a > quarter of the vmalloc space. > > Now, I think we all agree that these are not necessarily recommended > configurations but we should not be breaking them for the hell of it > either. > > How about leaving flatmem as it is and have an on-demand allocation > model that just works with sparsemem? A 128MB section on 64 bit > "only" needs order-7 pages, but we satisfy order-9 THP allocations all > the time during runtime, so this may just work. > I agree to Johannes' option. Thanks, -Kame