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=-8.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS 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 C04B5C43331 for ; Wed, 20 Jan 2021 10:25:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 770E42333B for ; Wed, 20 Jan 2021 10:25:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732506AbhATKS5 (ORCPT ); Wed, 20 Jan 2021 05:18:57 -0500 Received: from mx2.suse.de ([195.135.220.15]:57416 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730504AbhATJ7v (ORCPT ); Wed, 20 Jan 2021 04:59:51 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 4E0D5AC97; Wed, 20 Jan 2021 09:59:10 +0000 (UTC) Date: Wed, 20 Jan 2021 10:59:05 +0100 From: Oscar Salvador To: Mike Kravetz Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Michal Hocko , Naoya Horiguchi , Muchun Song , David Hildenbrand , Matthew Wilcox , Andrew Morton Subject: Re: [PATCH v2 2/5] hugetlb: convert page_huge_active() HPageMigratable flag Message-ID: <20210120095905.GA4752@localhost.localdomain> References: <20210120013049.311822-1-mike.kravetz@oracle.com> <20210120013049.311822-3-mike.kravetz@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210120013049.311822-3-mike.kravetz@oracle.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 19, 2021 at 05:30:46PM -0800, Mike Kravetz wrote: > Use the new hugetlb page specific flag HPageMigratable to replace the > page_huge_active interfaces. By it's name, page_huge_active implied > that a huge page was on the active list. However, that is not really > what code checking the flag wanted to know. It really wanted to determine > if the huge page could be migrated. This happens when the page is actually > added the page cache and/or task page table. This is the reasoning behind > the name change. > > The VM_BUG_ON_PAGE() calls in the *_huge_active() interfaces are not > really necessary as we KNOW the page is a hugetlb page. Therefore, they > are removed. > > The routine page_huge_active checked for PageHeadHuge before testing the > active bit. This is unnecessary in the case where we hold a reference or > lock and know it is a hugetlb head page. page_huge_active is also called > without holding a reference or lock (scan_movable_pages), and can race with > code freeing the page. The extra check in page_huge_active shortened the > race window, but did not prevent the race. Offline code calling > scan_movable_pages already deals with these races, so removing the check > is acceptable. Add comment to racy code. > > Signed-off-by: Mike Kravetz Hi Mike, This comment addresses both this patch and the next one. Instead of putting the SetHPageMigratable flag spread over the allocation paths, would it make more sense to place it in alloc_huge_page before returning the page? Then we could opencode SetHPageMigratableIfSupported right there. I might be missing something and this might not be possible, but if it is, it would look cleaner and more logical to me. -- Oscar Salvador SUSE L3