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=-5.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,USER_AGENT_MUTT autolearn=ham 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 9B2AFC43381 for ; Tue, 26 Mar 2019 10:17:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5755620857 for ; Tue, 26 Mar 2019 10:17:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1553595434; bh=tpyOwrolBJY4nPL6vIRppBHnolucs6Y2R/jwk2Mi9rg=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=uLap7prLY6P9WAVUHyzcBNNiTPX2DrhTRejyGYFshDawIvFiHi4asb59PJbmJSBK1 lGYgXz5QZexVj3AEyUju8nx6gGpNvue7swOARy6ZcH9TzM8n6y7FJ/F4hDwy6Myqnl E9cVaprV2BE0iXe07KKpz9jw3gzFnVjeCi/p6Og4= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731261AbfCZKRN (ORCPT ); Tue, 26 Mar 2019 06:17:13 -0400 Received: from mx2.suse.de ([195.135.220.15]:50962 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726413AbfCZKRM (ORCPT ); Tue, 26 Mar 2019 06:17:12 -0400 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 7FC8DAEDB; Tue, 26 Mar 2019 10:17:11 +0000 (UTC) Date: Tue, 26 Mar 2019 11:17:10 +0100 From: Michal Hocko To: Baoquan He Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, rppt@linux.ibm.com, osalvador@suse.de, willy@infradead.org, william.kucharski@oracle.com Subject: Re: [PATCH v2 2/4] mm/sparse: Optimize sparse_add_one_section() Message-ID: <20190326101710.GN28406@dhcp22.suse.cz> References: <20190326090227.3059-1-bhe@redhat.com> <20190326090227.3059-3-bhe@redhat.com> <20190326092936.GK28406@dhcp22.suse.cz> <20190326100817.GV3659@MiWiFi-R3L-srv> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190326100817.GV3659@MiWiFi-R3L-srv> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue 26-03-19 18:08:17, Baoquan He wrote: > On 03/26/19 at 10:29am, Michal Hocko wrote: > > On Tue 26-03-19 17:02:25, Baoquan He wrote: > > > Reorder the allocation of usemap and memmap since usemap allocation > > > is much simpler and easier. Otherwise hard work is done to make > > > memmap ready, then have to rollback just because of usemap allocation > > > failure. > > > > Is this really worth it? I can see that !VMEMMAP is doing memmap size > > allocation which would be 2MB aka costly allocation but we do not do > > __GFP_RETRY_MAYFAIL so the allocator backs off early. > > In !VMEMMAP case, it truly does simple allocation directly. surely > usemap which size is 32 is smaller. So it doesn't matter that much who's > ahead or who's behind. However, this benefit a little in VMEMMAP case. How does it help there? The failure should be even much less probable there because we simply fall back to a small 4kB pages and those essentially never fail. > And this make code a little cleaner, e.g the error handling at the end > is taken away. > > > > > > And also check if section is present earlier. Then don't bother to > > > allocate usemap and memmap if yes. > > > > Moving the check up makes some sense. > > > > > Signed-off-by: Baoquan He > > > > The patch is not incorrect but I am wondering whether it is really worth > > it for the current code base. Is it fixing anything real or it is a mere > > code shuffling to please an eye? > > It's not a fixing, just a tiny code refactorying inside > sparse_add_one_section(), seems it doesn't worsen thing if I got the > !VMEMMAP case correctly, not quite sure. I am fine to drop it if it's > not worth. I could miss something in different cases. Well, I usually prefer to not do micro-optimizations in a code that really begs for a much larger surgery. There are other people working on the code and patches like these might get into the way and cuase conflicts without a very good justification. -- Michal Hocko SUSE Labs