Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753290AbbBXWQw (ORCPT ); Tue, 24 Feb 2015 17:16:52 -0500 Received: from mail-lb0-f177.google.com ([209.85.217.177]:37798 "EHLO mail-lb0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753182AbbBXWQu (ORCPT ); Tue, 24 Feb 2015 17:16:50 -0500 MIME-Version: 1.0 In-Reply-To: References: <1424801964-1602-1-git-send-email-mhocko@suse.cz> <20150224191127.GA14718@phnom.home.cmpxchg.org> Date: Wed, 25 Feb 2015 01:16:49 +0300 Message-ID: Subject: Re: [PATCH] mm, oom: do not fail __GFP_NOFAIL allocation if oom killer is disbaled From: Konstantin Khlebnikov To: Johannes Weiner Cc: Michal Hocko , Andrew Morton , David Rientjes , "\\Rafael J. Wysocki\\" , Tetsuo Handa , "linux-mm@kvack.org" , LKML Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3630 Lines: 84 On Wed, Feb 25, 2015 at 1:09 AM, Konstantin Khlebnikov wrote: > On Tue, Feb 24, 2015 at 10:11 PM, Johannes Weiner wrote: >> On Tue, Feb 24, 2015 at 07:19:24PM +0100, Michal Hocko wrote: >>> Tetsuo Handa has pointed out that __GFP_NOFAIL allocations might fail >>> after OOM killer is disabled if the allocation is performed by a >>> kernel thread. This behavior was introduced from the very beginning by >>> 7f33d49a2ed5 (mm, PM/Freezer: Disable OOM killer when tasks are frozen). >>> This means that the basic contract for the allocation request is broken >>> and the context requesting such an allocation might blow up unexpectedly. >>> >>> There are basically two ways forward. >>> 1) move oom_killer_disable after kernel threads are frozen. This has a >>> risk that the OOM victim wouldn't be able to finish because it would >>> depend on an already frozen kernel thread. This would be really >>> tricky to debug. >>> 2) do not fail GFP_NOFAIL allocation no matter what and risk a potential >>> Freezable kernel threads will loop and fail the suspend. Incidental >>> allocations after kernel threads are frozen will at least dump a >>> warning - if we are lucky and the serial console is still active of >>> course... >>> >>> This patch implements the later option because it is safer. We would see >>> warnings rather than allocation failures for the kernel threads which >>> would blow up otherwise and have a higher chances to identify >>> __GFP_NOFAIL users from deeper pm code. >>> >>> Signed-off-by: Michal Hocko >>> --- >>> >>> We haven't seen any bug reports >>> >>> mm/oom_kill.c | 8 ++++++++ >>> 1 file changed, 8 insertions(+) >>> >>> diff --git a/mm/oom_kill.c b/mm/oom_kill.c >>> index 642f38cb175a..ea8b443cd871 100644 >>> --- a/mm/oom_kill.c >>> +++ b/mm/oom_kill.c >>> @@ -772,6 +772,10 @@ out: >>> schedule_timeout_killable(1); >>> } >>> >>> +static DEFINE_RATELIMIT_STATE(oom_disabled_rs, >>> + DEFAULT_RATELIMIT_INTERVAL, >>> + DEFAULT_RATELIMIT_BURST); >>> + >>> /** >>> * out_of_memory - tries to invoke OOM killer. >>> * @zonelist: zonelist pointer >>> @@ -792,6 +796,10 @@ bool out_of_memory(struct zonelist *zonelist, gfp_t gfp_mask, >>> if (!oom_killer_disabled) { >>> __out_of_memory(zonelist, gfp_mask, order, nodemask, force_kill); >>> ret = true; >>> + } else if (gfp_mask & __GFP_NOFAIL) { >>> + if (__ratelimit(&oom_disabled_rs)) >>> + WARN(1, "Unable to make forward progress for __GFP_NOFAIL because OOM killer is disbaled\n"); >>> + ret = true; >> >> I'm fine with keeping the allocation looping, but is that message >> helpful? It seems completely useless to the user encountering it. Is >> it going to help kernel developers when we get a bug report with it? >> >> WARN_ON_ONCE()? > > maybe panic() ? > > If somebody turns off oom-killer it seems he's pretty sure that he has > enough memory. Ah, that's used in freeze/suspend code. I thought that some kind of sysctl for brave sysadmins. > >> >> -- >> 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/