From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx173.postini.com [74.125.245.173]) by kanga.kvack.org (Postfix) with SMTP id 6BAB36B0070 for ; Thu, 15 Nov 2012 19:40:22 -0500 (EST) Received: by mail-pa0-f41.google.com with SMTP id fa10so1603236pad.14 for ; Thu, 15 Nov 2012 16:40:21 -0800 (PST) Message-ID: <50A58B6E.8090609@gmail.com> Date: Fri, 16 Nov 2012 08:40:14 +0800 From: Jaegeuk Hanse MIME-Version: 1.0 Subject: Re: [PATCH] tmpfs: fix shmem_getpage_gfp VM_BUG_ON References: <20121025023738.GA27001@redhat.com> <20121101191052.GA5884@redhat.com> <20121101232030.GA25519@redhat.com> <20121102014336.GA1727@redhat.com> <20121106135402.GA3543@redhat.com> <50A30ADD.9000209@gmail.com> <50A49C46.9040406@gmail.com> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Hugh Dickins Cc: Dave Jones , Andrew Morton , Johannes Weiner , linux-mm@kvack.org, linux-kernel@vger.kernel.org On 11/16/2012 03:56 AM, Hugh Dickins wrote: > Offtopic... > > On Thu, 15 Nov 2012, Jaegeuk Hanse wrote: >> Another question. Why the function shmem_fallocate which you add to kernel >> need call shmem_getpage? > Because shmem_getpage(_gfp) is where shmem's > page lookup and allocation complexities are handled. > > I assume the question behind your question is: why does shmem actually > allocate pages for its fallocate, instead of just reserving the space? Yeah, this is what I want to know. > > I did play with just reserving the space, with more special entries in > the radix_tree to note the reservations made. It should be doable for > the vm_enough_memory and sbinfo->used_blocks reservations. > > What absolutely deterred me from taking that path was the mem_cgroup > case: shmem and swap and memcg are not easy to get working right together, > and nobody would thank me for complicating memcg just for shmem_fallocate. > > By allocating pages, the pre-existing memcg code just works; if we used > reservations instead, we would have to track their memcg charges in some > additional new way. I see no justification for that complication. Oh, I see, thanks Hugh. :-) > Hugh -- 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