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=-5.1 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, 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 DBAAEC4363D for ; Mon, 5 Oct 2020 15:08:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 92F7B2100A for ; Mon, 5 Oct 2020 15:08:08 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="K6/WmPyY" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726637AbgJEPIH (ORCPT ); Mon, 5 Oct 2020 11:08:07 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45452 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725970AbgJEPIG (ORCPT ); Mon, 5 Oct 2020 11:08:06 -0400 Received: from mail-lj1-x244.google.com (mail-lj1-x244.google.com [IPv6:2a00:1450:4864:20::244]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 55C6FC0613CE; Mon, 5 Oct 2020 08:08:06 -0700 (PDT) Received: by mail-lj1-x244.google.com with SMTP id a5so2189759ljj.11; Mon, 05 Oct 2020 08:08:06 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:date:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=y/jbq/dvc0SeEAuNgs8PeopdIcqnz5xE9+lszm120Vg=; b=K6/WmPyYCS3Rp8ku15cnJNHN00NAvg3pv5av7mmklhJfeeND9Gr57YIUr5oUbLr4i+ moeXbFdzQ5FDo2540XrC2ZpD3GlrHYo04HwFZ0GX/mz/V0FGv1iZrtRzRd+zBVdKWLev OiIHRmxkBJ3Uu7/MrJGkQMyH0Gd3wMlKXVob4wzbZcgPPi2ttIeoMzhwIyuIkcMvzgrf Lun1kRFhEIi0Tfoxa9SimQEu2pUqFWmF8xtcYXlBJikQY9GahZxMylUD4ZFKQixYGh9X FNBzPAndi+Fp0F6Y9KVcYeOPfioAQ8E4dPMrRJMIoYfN+BijZ/vcRnEcoFpSCy4e4mDu i5gg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:date:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=y/jbq/dvc0SeEAuNgs8PeopdIcqnz5xE9+lszm120Vg=; b=Kkq9P/FxkCVc5EcTgObxtEHvN8agJ7gwuePZrkE4PPcZCemaABLX4soANduE95biit hh6JqHLKmGJEM8RlfnRVZvmgqFpGp9VqB0pWvounCLib5tpfxA31YZUVVVIUt5BdfBst CIQ0faQcXGN+1WlLv1c7wZcfoKDYAhl6W74+4PpYlnfxnyWJ63M2Q/OlSyfr6r4Fkfx/ 3xnZT9EMlMM6Ppbe0RrkRo0hvAdpljiCyr4+YpB20yxiuPRx/6lfPlx0FJZ13sn0EPiT 6pnT6kBKeIgIvAYDiban9HET24IYYXqrfiEDh7My5iOy5vFRDX/pS5+SznyF+fq0Mcxw L8Qw== X-Gm-Message-State: AOAM533RfsAJ7/xNxT6Nfja2bvm1gDJfcQ26rrpM1seUUPr1aX/TUtz7 /SbNefb/s5reQlwx1MGiPfA= X-Google-Smtp-Source: ABdhPJwJCWZY1Ta3clt2a8+QT8HNjjnHTD5+j6kZdK+JedNK3x/DxK2R5Lq8sgokrenP6Q/9uJLfsw== X-Received: by 2002:a2e:8702:: with SMTP id m2mr49631lji.49.1601910484580; Mon, 05 Oct 2020 08:08:04 -0700 (PDT) Received: from pc636 (h5ef52e31.seluork.dyn.perspektivbredband.net. [94.245.46.49]) by smtp.gmail.com with ESMTPSA id 18sm3305lfz.141.2020.10.05.08.08.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 05 Oct 2020 08:08:03 -0700 (PDT) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Mon, 5 Oct 2020 17:08:01 +0200 To: Michal Hocko Cc: Mel Gorman , 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: <20201005150801.GC17959@pc636> 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> <20201002090507.GB4555@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201002090507.GB4555@dhcp22.suse.cz> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Oct 02, 2020 at 11:05:07AM +0200, Michal Hocko wrote: > 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) > Agree. Even though i see that some code should be adjusted for it. There are a few users of the __get_free_page(0); So, need to double check it: [ 0.650351] BUG: kernel NULL pointer dereference, address: 0000000000000010 [ 0.651083] #PF: supervisor read access in kernel mode [ 0.651639] #PF: error_code(0x0000) - not-present page [ 0.652200] PGD 0 P4D 0 [ 0.652523] Oops: 0000 [#1] SMP NOPTI [ 0.652668] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.9.0-rc7-next-20200930+ #140 [ 0.652668] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014 [ 0.652668] RIP: 0010:__find_event_file+0x21/0x80 Apart of that. There is a post_alloc_hook(), that gets called from the prep_new_page(). If "debug page alloc enabled", it maps a page for debug purposes invoking kernel_map_pages(). __kernel_map_pages() is ARCH specific. For example, powerpc variant uses sleep-able locks what can be easily converted to raw variant. -- Vlad Rezki