From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 86AB9C2BB1D for ; Tue, 14 Apr 2020 19:26:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5D06720787 for ; Tue, 14 Apr 2020 19:26:48 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=nvidia.com header.i=@nvidia.com header.b="IerDSP3y" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2504703AbgDNT0o (ORCPT ); Tue, 14 Apr 2020 15:26:44 -0400 Received: from hqnvemgate26.nvidia.com ([216.228.121.65]:10012 "EHLO hqnvemgate26.nvidia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2504673AbgDNT0D (ORCPT ); Tue, 14 Apr 2020 15:26:03 -0400 Received: from hqpgpgate101.nvidia.com (Not Verified[216.228.121.13]) by hqnvemgate26.nvidia.com (using TLS: TLSv1.2, DES-CBC3-SHA) id ; Tue, 14 Apr 2020 12:05:45 -0700 Received: from hqmail.nvidia.com ([172.20.161.6]) by hqpgpgate101.nvidia.com (PGP Universal service); Tue, 14 Apr 2020 12:05:58 -0700 X-PGP-Universal: processed; by hqpgpgate101.nvidia.com on Tue, 14 Apr 2020 12:05:58 -0700 Received: from DRHQMAIL107.nvidia.com (10.27.9.16) by HQMAIL107.nvidia.com (172.20.187.13) with Microsoft SMTP Server (TLS) id 15.0.1473.3; Tue, 14 Apr 2020 19:05:58 +0000 Received: from [10.2.59.2] (10.124.1.5) by DRHQMAIL107.nvidia.com (10.27.9.16) with Microsoft SMTP Server (TLS) id 15.0.1473.3; Tue, 14 Apr 2020 19:05:57 +0000 Subject: Re: [PATCH 1/2] mm: clarify __GFP_MEMALLOC usage To: NeilBrown , Andrew Morton CC: David Rientjes , Michal Hocko , Joel Fernandes , "Paul E. McKenney" , , LKML References: <20200403083543.11552-1-mhocko@kernel.org> <20200403083543.11552-2-mhocko@kernel.org> <87blo8xnz2.fsf@notabene.neil.brown.name> <20200406070137.GC19426@dhcp22.suse.cz> <4f861f07-4b47-8ddc-f783-10201ea302d3@nvidia.com>

<20200413191532.6b234b50caea9134fb95a151@linux-foundation.org> <87h7xmu3di.fsf@notabene.neil.brown.name> X-Nvconfidentiality: public From: John Hubbard Message-ID: Date: Tue, 14 Apr 2020 12:05:57 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <87h7xmu3di.fsf@notabene.neil.brown.name> X-Originating-IP: [10.124.1.5] X-ClientProxiedBy: HQMAIL105.nvidia.com (172.20.187.12) To DRHQMAIL107.nvidia.com (10.27.9.16) Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nvidia.com; s=n1; t=1586891145; bh=g4yF/XOBRuoNrZ1hb1bn5M1jI7/I+PjWefBEgTSY1Zo=; h=X-PGP-Universal:Subject:To:CC:References:X-Nvconfidentiality:From: Message-ID:Date:User-Agent:MIME-Version:In-Reply-To: X-Originating-IP:X-ClientProxiedBy:Content-Type:Content-Language: Content-Transfer-Encoding; b=IerDSP3yz3nDr3jFx0NePg9qqclc7xk4zAzjvw4VqWUrv3Rs0e6irKHec+TsoEAYl P+JBbgsYVQ8GYKW3lXSqkWje2mjJ9VdQ+iC0RHWGF3W3jpw9Wj55mNdL5mfDUd1O6n fW4GxtZFrNtclNxV9UE7RvRy2ijcfEuBWGjZ+b92OD1d11IbnWVCjuC04/QzZjdxWa qdix9tNV68rEGUO55O4zNCM+zs+UNf6OzOSwCBjWrtI71Xn2n/W0UT69ml4bTRIqaQ 5RcaKMqMHHgMuyF1pOc2kGB/HwdxhjO5nvTlLcduXKNdoRXBRERJM21e6ntBYOmZLM BC31nWOOy04dQ== Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020-04-13 20:56, NeilBrown wrote: > On Mon, Apr 13 2020, Andrew Morton wrote: > >> I've rather lost the plot with this little patch. Is the below >> suitable, or do we think that changes are needed? >> I recall we were trying to talk Neil into adding some of his writings into Documentation/core-api/memory-allocation.rst, and then refer to that from here. But that would be a separate patch I think. thanks, -- John Hubbard NVIDIA >> >> From: Michal Hocko >> Subject: mm: clarify __GFP_MEMALLOC usage >> >> It seems that the existing documentation is not explicit about the >> expected usage and potential risks enough. While it is calls out that >> users have to free memory when using this flag it is not really apparent >> that users have to careful to not deplete memory reserves and that they >> should implement some sort of throttling wrt. freeing process. >> >> This is partly based on Neil's explanation [1]. >> >> Let's also call out that a pre allocated pool allocator should be >> considered. >> >> [1] http://lkml.kernel.org/r/877dz0yxoa.fsf@notabene.neil.brown.name >> >> [akpm@linux-foundation.org: coding style fixes] >> Link: http://lkml.kernel.org/r/20200403083543.11552-2-mhocko@kernel.org >> Signed-off-by: Michal Hocko >> Cc: David Rientjes >> Cc: Joel Fernandes >> Cc: Neil Brown >> Cc: Paul E. McKenney >> Cc: John Hubbard >> [mhocko@kernel.org: update] >> Link: http://lkml.kernel.org/r/20200406070137.GC19426@dhcp22.suse.cz >> Signed-off-by: Andrew Morton >> --- >> >> include/linux/gfp.h | 5 +++++ >> 1 file changed, 5 insertions(+) >> >> --- a/include/linux/gfp.h~mm-clarify-__gfp_memalloc-usage >> +++ a/include/linux/gfp.h >> @@ -110,6 +110,11 @@ struct vm_area_struct; >> * the caller guarantees the allocation will allow more memory to be freed >> * very shortly e.g. process exiting or swapping. Users either should >> * be the MM or co-ordinating closely with the VM (e.g. swap over NFS). >> + * Users of this flag have to be extremely careful to not deplete the reserve >> + * completely and implement a throttling mechanism which controls the >> + * consumption of the reserve based on the amount of freed memory. >> + * Usage of a pre-allocated pool (e.g. mempool) should be always considered >> + * before using this flag. > > I particularly don't like the connection between the consumption and the > amount freed. I don't think that say anything useful and it misses the > main point which, I think, is having a bound on total usage. > > Nichal's previous proposal is, I think, the best concrete proposal so > far. > > NeilBrown > >> * >> * %__GFP_NOMEMALLOC is used to explicitly forbid access to emergency reserves. >> * This takes precedence over the %__GFP_MEMALLOC flag if both are set. >> _