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=-4.0 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,FSL_HELO_FAKE,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 A9FD7C71156 for ; Wed, 2 Dec 2020 17:55:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4B41822203 for ; Wed, 2 Dec 2020 17:55:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728114AbgLBRzO (ORCPT ); Wed, 2 Dec 2020 12:55:14 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46536 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726485AbgLBRzO (ORCPT ); Wed, 2 Dec 2020 12:55:14 -0500 Received: from mail-pj1-x1042.google.com (mail-pj1-x1042.google.com [IPv6:2607:f8b0:4864:20::1042]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 34E72C0613D6; Wed, 2 Dec 2020 09:54:34 -0800 (PST) Received: by mail-pj1-x1042.google.com with SMTP id h7so857983pjk.1; Wed, 02 Dec 2020 09:54:34 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=UNKWdsiogoUet2aqz/JwzPrZ2X40+ZcKRQbStzwokt0=; b=Ch7jlmfJ3ZG0zz+DkXI5UWNXdzW8xdMQrZ11QsjWzilKSCB+iWXcZp192Cx7al8zAo G/Piuv+Qqy22klp5kV8fnf7CWhxl0uqAd4CZkvf9nknoc+WzgvWLbIHhC+qPxUsXtcyg CBfQuttlobVsjMVoyqplhWPwpAUDGUG2DM+Z9nFSy3XC3nP6PVYsOTgtf4OSmRl4ysxm J+7H9NRr2vlLq8yFPPhp+pt8AkrBRmQMOXnFFnnMe8eF534oC8CUhJLiLjNvxktu1jxC zzHm8fcGik37MIaJ4UEfWkywvgLO7ua8DwTGm20sduE1+xDhG62iHg9PXhkhvLUF7oE8 Nn3Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:from:to:cc:subject:message-id :references:mime-version:content-disposition:in-reply-to; bh=UNKWdsiogoUet2aqz/JwzPrZ2X40+ZcKRQbStzwokt0=; b=jnnotY1UPQK2G2szSO4OLekM/2+Jm2rv6Vb8eAlmYwiViDLIb5J8j3r925VYR3OuyQ HeGSI2lZwI9Pj7M36yFNWEP9Kpjb/yASUlaxPhT72RXM3O8sOLrYvDgVtNHQ8d0W/0/j lu+l0tPPL+6ed3Q/aShxEjVHf0ZYIBG3jhgDBkX8uDtPsyUknPU++qChlrXtsCYyL5ue 9f2lEYra73lUq8YQCgKHa+dZWJStB3Xk8eDwBiJP7/wAvsTF3ou6jMmGv3t5JLJ5Jj6S Id5VumAOq016uAOpefhAypCyWIuZnpZLqabWtse+RqjA7MaRplKmWMjPNaVsHPqrbTu1 HKXw== X-Gm-Message-State: AOAM532sz5+y5IJzqM7rhsfi248XFAlBvAyW0E0EUvC6Kz93guQVaSUs VUXFSYKMVhi7VprigGVqH3A= X-Google-Smtp-Source: ABdhPJwBaisCw9eYl7Ol+VCo/5w7dy23oiZjb0JInGv5r1eT2cOTilc+02VuZ6NOT1gRo3hlHWW6/g== X-Received: by 2002:a17:902:eb0c:b029:da:51da:cdac with SMTP id l12-20020a170902eb0cb02900da51dacdacmr3686446plb.4.1606931673751; Wed, 02 Dec 2020 09:54:33 -0800 (PST) Received: from google.com ([2620:15c:211:201:7220:84ff:fe09:5e58]) by smtp.gmail.com with ESMTPSA id t9sm282269pjq.46.2020.12.02.09.54.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 02 Dec 2020 09:54:32 -0800 (PST) Sender: Minchan Kim Date: Wed, 2 Dec 2020 09:54:29 -0800 From: Minchan Kim To: Michal Hocko Cc: David Hildenbrand , Andrew Morton , LKML , linux-mm , hyesoo.yu@samsung.com, willy@infradead.org, iamjoonsoo.kim@lge.com, vbabka@suse.cz, surenb@google.com, pullip.cho@samsung.com, joaodias@google.com, hridya@google.com, sumit.semwal@linaro.org, john.stultz@linaro.org, Brian.Starkey@arm.com, linux-media@vger.kernel.org, devicetree@vger.kernel.org, robh@kernel.org, christian.koenig@amd.com, linaro-mm-sig@lists.linaro.org Subject: Re: [PATCH v2 2/4] mm: introduce cma_alloc_bulk API Message-ID: References: <20201201175144.3996569-1-minchan@kernel.org> <20201201175144.3996569-3-minchan@kernel.org> <8f006a4a-c21d-9db3-5493-fb1cc651b0cf@redhat.com> <20201202154915.GU17338@dhcp22.suse.cz> <20201202164834.GV17338@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201202164834.GV17338@dhcp22.suse.cz> Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org On Wed, Dec 02, 2020 at 05:48:34PM +0100, Michal Hocko wrote: > On Wed 02-12-20 08:15:49, Minchan Kim wrote: > > On Wed, Dec 02, 2020 at 04:49:15PM +0100, Michal Hocko wrote: > [...] > > > Well, what I can see is that this new interface is an antipatern to our > > > allocation routines. We tend to control allocations by gfp mask yet you > > > are introducing a bool parameter to make something faster... What that > > > really means is rather arbitrary. Would it make more sense to teach > > > cma_alloc resp. alloc_contig_range to recognize GFP_NOWAIT, GFP_NORETRY resp. > > > GFP_RETRY_MAYFAIL instead? > > > > If we use cma_alloc, that interface requires "allocate one big memory > > chunk". IOW, return value is just struct page and expected that the page > > is a big contiguos memory. That means it couldn't have a hole in the > > range. > > However the idea here, what we asked is much smaller chunk rather > > than a big contiguous memory so we could skip some of pages if they are > > randomly pinned(long-term/short-term whatever) and search other pages > > in the CMA area to avoid long stall. Thus, it couldn't work with exising > > cma_alloc API with simple gfp_mak. > > I really do not see that as something really alient to the cma_alloc > interface. All you should care about, really, is what size of the object > you want and how hard the system should try. If you have a problem with > an internal implementation of CMA and how it chooses a range and deal > with pinned pages then it should be addressed inside the CMA allocator. > I suspect that you are effectivelly trying to workaround those problems > by a side implementation with a slightly different API. Or maybe I still > do not follow the actual problem. > > > > I am not deeply familiar with the cma allocator so sorry for a > > > potentially stupid question. Why does a bulk interface performs better > > > than repeated calls to cma_alloc? Is this because a failure would help > > > to move on to the next pfn range while a repeated call would have to > > > deal with the same range? > > > > Yub, true with other overheads(e.g., migration retrial, waiting writeback > > PCP/LRU draining IPI) > > Why cannot this be implemented in the cma_alloc layer? I mean you can > cache failed cases and optimize the proper pfn range search. So do you suggest this? enum cma_alloc_mode { CMA_ALLOC_NORMAL, CMA_ALLOC_FAIL_FAST, }; struct page *cma_alloc(struct cma *cma, size_t count, unsigned int align, enum cma_alloc_mode mode); >From now on, cma_alloc will keep last failed pfn and then start to search from the next pfn for both CMA_ALLOC_NORMAL and CMA_ALLOC_FAIL_FAST if requested size from the cached pfn is okay within CMA area and then wraparound it couldn't find right pages from the cached pfn. Othewise, the cached pfn will reset to the zero so that it starts the search from the 0. I like the idea since it's general improvement, I think. Furthemore, With CMA_ALLOC_FAIL_FAST, it could avoid several overheads at the cost of sacrificing allocation success ratio like GFP_NORETRY. I think that would solve the issue with making the API more flexible. Before diving into it, I'd like to confirm we are on same page. Please correct me if I misunderstood. David, any objection?