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=-5.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 816DCC4727F for ; Fri, 2 Oct 2020 09:05:12 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id E4B0F2068E for ; Fri, 2 Oct 2020 09:05:11 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=suse.com header.i=@suse.com header.b="nBaClv4g" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E4B0F2068E Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 03DC06B005D; Fri, 2 Oct 2020 05:05:11 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id F304A900002; Fri, 2 Oct 2020 05:05:10 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id DF7A96B0068; Fri, 2 Oct 2020 05:05:10 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0184.hostedemail.com [216.40.44.184]) by kanga.kvack.org (Postfix) with ESMTP id AF2C66B005D for ; Fri, 2 Oct 2020 05:05:10 -0400 (EDT) Received: from smtpin15.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 4092C180AD802 for ; Fri, 2 Oct 2020 09:05:10 +0000 (UTC) X-FDA: 77326401180.15.lunch34_3113673271a2 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin15.hostedemail.com (Postfix) with ESMTP id 14A341814B0CC for ; Fri, 2 Oct 2020 09:05:10 +0000 (UTC) X-HE-Tag: lunch34_3113673271a2 X-Filterd-Recvd-Size: 4990 Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by imf20.hostedemail.com (Postfix) with ESMTP for ; Fri, 2 Oct 2020 09:05:09 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1601629508; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=NLWsHd/XYO6vX/kTuPru1/vkApAYvvP2ucBNJ3kKVJc=; b=nBaClv4gbAC5DRD/cBtVyI8bqQREp2ba72exdgoEbhBJpsfwpn/ZoB3oPxLsMABwnqlpRu HzEBZxVHxXQrmsKtRjP0XMUiPs1bX615oSEwHpwz9Nb/lecPKLCOrIUClTK6lUaxeOxGqW i/MSW4kEL6K8x/sZh3QhX/3UrPsQ7qE= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 4F805AC82; Fri, 2 Oct 2020 09:05:08 +0000 (UTC) Date: Fri, 2 Oct 2020 11:05:07 +0200 From: Michal Hocko To: Mel Gorman Cc: Uladzislau Rezki , Vlastimil Babka , LKML , RCU , linux-mm@kvack.org, Andrew Morton , "Paul E . McKenney" , Peter Zijlstra , Thomas Gleixner , "Theodore Y . Ts'o" , Joel Fernandes , Sebastian Andrzej Siewior , Oleksiy Avramchenko Subject: Re: [RFC-PATCH 2/4] mm: Add __rcu_alloc_page_lockless() func. Message-ID: <20201002090507.GB4555@dhcp22.suse.cz> References: <20200918194817.48921-1-urezki@gmail.com> <20200918194817.48921-3-urezki@gmail.com> <38f42ca1-ffcd-04a6-bf11-618deffa897a@suse.cz> <20200929220742.GB8768@pc636> <795d6aea-1846-6e08-ac1b-dbff82dd7133@suse.cz> <20201001192626.GA29606@pc636> <20201002071123.GB20872@dhcp22.suse.cz> <20201002085014.GC3227@techsingularity.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201002085014.GC3227@techsingularity.net> User-Agent: Mutt/1.10.1 (2018-07-13) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri 02-10-20 09:50:14, Mel Gorman wrote: > On Fri, Oct 02, 2020 at 09:11:23AM +0200, Michal Hocko wrote: > > On Thu 01-10-20 21:26:26, Uladzislau Rezki wrote: > > > > > > > > No, I meant going back to idea of new gfp flag, but adjust the implementation in > > > > the allocator (different from what you posted in previous version) so that it > > > > only looks at the flag after it tries to allocate from pcplist and finds out > > > > it's empty. So, no inventing of new page allocator entry points or checks such > > > > as the one you wrote above, but adding the new gfp flag in a way that it doesn't > > > > affect existing fast paths. > > > > > > > OK. Now i see. Please have a look below at the patch, so we fully understand > > > each other. If that is something that is close to your view or not: > > > > > > > > > t a/include/linux/gfp.h b/include/linux/gfp.h > > > index c603237e006c..7e613560a502 100644 > > > --- a/include/linux/gfp.h > > > +++ b/include/linux/gfp.h > > > @@ -39,8 +39,9 @@ struct vm_area_struct; > > > #define ___GFP_HARDWALL 0x100000u > > > #define ___GFP_THISNODE 0x200000u > > > #define ___GFP_ACCOUNT 0x400000u > > > +#define ___GFP_NO_LOCKS 0x800000u > > > > Even if a new gfp flag gains a sufficient traction and support I am > > _strongly_ opposed against consuming another flag for that. Bit space is > > limited. > > That is definitely true. I'm not happy with the GFP flag at all, the > comment is at best a damage limiting move. It still would be better for > a memory pool to be reserved and sized for critical allocations. Completely agreed. The only existing usecase is so special cased that a dedicated pool is not only easier to maintain but it should be also much better tuned for the specific workload. Something not really feasible with the allocator. > > Besides that we certainly do not want to allow craziness like > > __GFP_NO_LOCK | __GFP_RECLAIM (and similar), do we? > > That would deserve to be taken to a dumpster and set on fire. The flag > combination could be checked in the allocator but the allocator path fast > paths are bad enough already. If a new allocation/gfp mode is absolutely necessary then I believe that the most reasoanble way forward would be #define GFP_NO_LOCK ((__force gfp_t)0) and explicitly document it as a final flag to use without any further modifiers. Yeah there are some that could be used potentially - e.g. zone specifiers, __GFP_ZERO and likely few others. But support for those can be added when there is an actual and reasonable demand. I would also strongly argue against implementation alowing to fully consume pcp free pages. -- Michal Hocko SUSE Labs