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=-2.5 required=3.0 tests=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 B0DCCC3A5A7 for ; Tue, 3 Sep 2019 19:18:23 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 7E11720820 for ; Tue, 3 Sep 2019 19:18:23 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7E11720820 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 1CD356B0005; Tue, 3 Sep 2019 15:18:23 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 1A59B6B0006; Tue, 3 Sep 2019 15:18:23 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 0BA836B0007; Tue, 3 Sep 2019 15:18:23 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0024.hostedemail.com [216.40.44.24]) by kanga.kvack.org (Postfix) with ESMTP id DE47B6B0005 for ; Tue, 3 Sep 2019 15:18:22 -0400 (EDT) Received: from smtpin29.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with SMTP id 70EE8180AD802 for ; Tue, 3 Sep 2019 19:18:22 +0000 (UTC) X-FDA: 75894570444.29.tree99_2bf6ae6a6bc35 X-HE-Tag: tree99_2bf6ae6a6bc35 X-Filterd-Recvd-Size: 3811 Received: from mx1.suse.de (mx2.suse.de [195.135.220.15]) by imf08.hostedemail.com (Postfix) with ESMTP for ; Tue, 3 Sep 2019 19:18:22 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id AFCC2AF10; Tue, 3 Sep 2019 19:18:20 +0000 (UTC) Date: Tue, 3 Sep 2019 21:18:19 +0200 From: Michal Hocko To: Matthew Wilcox Cc: William Kucharski , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, Dave Hansen , Song Liu , Bob Kasten , Mike Kravetz , Chad Mynhier , "Kirill A. Shutemov" , Johannes Weiner Subject: Re: [PATCH v5 1/2] mm: Allow the page cache to allocate large pages Message-ID: <20190903191819.GD14028@dhcp22.suse.cz> References: <20190902092341.26712-1-william.kucharski@oracle.com> <20190902092341.26712-2-william.kucharski@oracle.com> <20190903115748.GS14028@dhcp22.suse.cz> <20190903121155.GD29434@bombadil.infradead.org> <20190903121952.GU14028@dhcp22.suse.cz> <20190903162831.GI29434@bombadil.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190903162831.GI29434@bombadil.infradead.org> 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 Tue 03-09-19 09:28:31, Matthew Wilcox wrote: > On Tue, Sep 03, 2019 at 02:19:52PM +0200, Michal Hocko wrote: > > On Tue 03-09-19 05:11:55, Matthew Wilcox wrote: > > > On Tue, Sep 03, 2019 at 01:57:48PM +0200, Michal Hocko wrote: > > > > On Mon 02-09-19 03:23:40, William Kucharski wrote: > > > > > Add an 'order' argument to __page_cache_alloc() and > > > > > do_read_cache_page(). Ensure the allocated pages are compound pages. > > > > > > > > Why do we need to touch all the existing callers and change them to use > > > > order 0 when none is actually converted to a different order? This just > > > > seem to add a lot of code churn without a good reason. If anything I > > > > would simply add __page_cache_alloc_order and make __page_cache_alloc > > > > call it with order 0 argument. > > > > > > Patch 2/2 uses a non-zero order. > > > > It is a new caller and it can use a new function right? > > > > > I agree it's a lot of churn without > > > good reason; that's why I tried to add GFP_ORDER flags a few months ago. > > > Unfortunately, you didn't like that approach either. > > > > Is there any future plan that all/most __page_cache_alloc will get a > > non-zero order argument? > > I'm not sure about "most". It will certainly become more common, as > far as I can tell. I would personally still go with __page_cache_alloc_order way, but this is up to you and other fs people what suits best. I was just surprised to see a lot of code churn when it was not really used in the second patch. That's why I brought it up. > > > > Also is it so much to ask callers to provide __GFP_COMP explicitly? > > > > > > Yes, it's an unreasonable burden on the callers. > > > > Care to exaplain why? __GFP_COMP tends to be used in the kernel quite > > extensively. > > Most of the places which call this function get their gfp_t from > mapping->gfp_mask. If we only want to allocate a single page, we > must not set __GFP_COMP. If we want to allocate a large page, we must > set __GFP_COMP. Rather than require individual filesystems to concern > themselves with this wart of the GFP interface, we can solve it in the > page cache. Fair enough. -- Michal Hocko SUSE Labs