From mboxrd@z Thu Jan 1 00:00:00 1970 From: Johannes Weiner Subject: Re: [PATCH 1/2] memcg: consistently use vmalloc for page_cgroup allocations Date: Fri, 5 Apr 2013 08:06:05 -0400 Message-ID: <20130405120604.GN1953@cmpxchg.org> References: <1365156072-24100-1-git-send-email-glommer@parallels.com> <1365156072-24100-2-git-send-email-glommer@parallels.com> Mime-Version: 1.0 Return-path: Content-Disposition: inline In-Reply-To: <1365156072-24100-2-git-send-email-glommer-bzQdu9zFT3WakBO8gow8eQ@public.gmane.org> Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Glauber Costa Cc: cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, kamezawa.hiroyu-+CUm20s59erQFUHtdCDX3A@public.gmane.org, Michal Hocko 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.