From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Subject: Re: [PATCH 0/2] Move away from non-failing small allocations Date: Mon, 16 Mar 2015 15:38:43 -0700 Message-ID: <20150316153843.af945a9e452404c22c4db999@linux-foundation.org> References: <1426107294-21551-1-git-send-email-mhocko@suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1426107294-21551-1-git-send-email-mhocko-AlSwsSmVLrQ@public.gmane.org> Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Michal Hocko Cc: Johannes Weiner , Dave Chinner , Mel Gorman , Rik van Riel , Wu Fengguang , linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, LKML , Linux API List-Id: linux-api@vger.kernel.org On Wed, 11 Mar 2015 16:54:52 -0400 Michal Hocko wrote: > as per discussion at LSF/MM summit few days back it seems there is a > general agreement on moving away from "small allocations do not fail" > concept. Such a change affects basically every part of the kernel and every kernel developer. I expect most developers will say "it works well enough and I'm not getting any bug reports so why should I spend time on this?". It would help if we were to explain the justification very clearly. https://lwn.net/Articles/636017/ is Jon's writeup of the conference discussion. Realistically, I don't think this overall effort will be successful - we'll add the knob, it won't get enough testing and any attempt to alter the default will be us deliberately destabilizing the kernel without knowing how badly :( I wonder if we can alter the behaviour only for filesystem code, so we constrain the new behaviour just to that code where we're having problems. Most/all fs code goes via vfs methods so there's a reasonably small set of places where we can call static inline void enter_fs_code(struct super_block *sb) { if (sb->my_small_allocations_can_fail) current->small_allocations_can_fail++; } that way (or something similar) we can select the behaviour on a per-fs basis and the rest of the kernel remains unaffected. Other subsystems can opt in as well.