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=-15.7 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 3456CC433E0 for ; Wed, 27 Jan 2021 10:28:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CAFF1206F4 for ; Wed, 27 Jan 2021 10:28:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235947AbhA0K2T (ORCPT ); Wed, 27 Jan 2021 05:28:19 -0500 Received: from mx2.suse.de ([195.135.220.15]:54844 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235846AbhA0K0F (ORCPT ); Wed, 27 Jan 2021 05:26:05 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1611743118; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=C/1GVgbi5JapDlkuAM1CT4D/SC46Mqf1KhShlAOrt0c=; b=nvVqjQA+BZk4AAMn9wowZvKRbsY5BPu9qDlfGcT7BisChiU3wPoG40hIr6BQ68Z0up2+Bl PkN8mOvcYzxnAhLMp0Wo+V5BW/71D04pHrdY7m80fi0ftG4V7vaWFvEuQ5kKVo3rcABTdh gcH+L4fCbzwsMZIx2Fzkz6aHRUIe6eU= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id AA4B7AD2B; Wed, 27 Jan 2021 10:25:18 +0000 (UTC) Date: Wed, 27 Jan 2021 11:25:17 +0100 From: Michal Hocko To: Mike Kravetz Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Naoya Horiguchi , Muchun Song , David Hildenbrand , Oscar Salvador , Matthew Wilcox , Miaohe Lin , Andrew Morton Subject: Re: [PATCH v3 2/5] hugetlb: convert page_huge_active() HPageMigratable flag Message-ID: <20210127102517.GG827@dhcp22.suse.cz> References: <20210122195231.324857-1-mike.kravetz@oracle.com> <20210122195231.324857-3-mike.kravetz@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210122195231.324857-3-mike.kravetz@oracle.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri 22-01-21 11:52:28, 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 to the page cache and/or task page table. This is the reasoning > behind the name change. yeah, definitely less confusing! > 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 > Reviewed-by: Oscar Salvador > Reviewed-by: Muchun Song > Reviewed-by: Miaohe Lin Acked-by: Michal Hocko One nit below [...] > diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h > index a7eb05315c6e..58be44a915d1 100644 > --- a/include/linux/hugetlb.h > +++ b/include/linux/hugetlb.h > @@ -480,9 +480,13 @@ unsigned long hugetlb_get_unmapped_area(struct file *file, unsigned long addr, > * HPG_restore_reserve - Set when a hugetlb page consumes a reservation at > * allocation time. Cleared when page is fully instantiated. Free > * routine checks flag to restore a reservation on error paths. > + * HPG_migratable - Set after a newly allocated page is added to the page > + * cache and/or page tables. Indicates the page is a candidate for > + * migration. The state change is synchronized by hugetlb_lock. Pls. > */ > enum hugetlb_page_flags { > HPG_restore_reserve = 0, > + HPG_migratable, > __NR_HPAGEFLAGS, > }; -- Michal Hocko SUSE Labs