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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,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 0E159C433DB for ; Fri, 19 Feb 2021 10:41:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B51AC64EBD for ; Fri, 19 Feb 2021 10:41:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230081AbhBSKlT (ORCPT ); Fri, 19 Feb 2021 05:41:19 -0500 Received: from mx2.suse.de ([195.135.220.15]:42242 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229998AbhBSKlN (ORCPT ); Fri, 19 Feb 2021 05:41:13 -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 7D483AC6E; Fri, 19 Feb 2021 10:40:32 +0000 (UTC) Date: Fri, 19 Feb 2021 11:40:30 +0100 From: Oscar Salvador To: Michal Hocko Cc: Andrew Morton , Mike Kravetz , David Hildenbrand , Muchun Song , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] mm: Make alloc_contig_range handle free hugetlb pages Message-ID: <20210219103943.GA19945@linux> References: <20210217100816.28860-1-osalvador@suse.de> <20210217100816.28860-2-osalvador@suse.de> <20210218100917.GA4842@localhost.localdomain> <20210218133250.GA7983@localhost.localdomain> <20210219090548.GA17266@linux> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Feb 19, 2021 at 10:56:42AM +0100, Michal Hocko wrote: > OK, this should work but I am really wondering whether it wouldn't be > just simpler to replace the old page by a new one in the free list > directly. Or is there any reason we have to go through the generic > helpers path? I mean something like this > > new_page = alloc_fresh_huge_page(); > if (!new_page) > goto fail; > spin_lock(hugetlb_lock); > if (!PageHuge(old_page)) { > /* freed from under us, nothing to do */ > __update_and_free_page(new_page); > goto unlock; > } > list_del(&old_page->lru); > __update_and_free_page(old_page); > __enqueue_huge_page(new_page); > unlock: > spin_unlock(hugetlb_lock); > > This will require to split update_and_free_page and enqueue_huge_page to > counters independent parts but that shouldn't be a big deal. But it will > also protect from any races. Not an act of beauty but seems less hackish > to me. On a closer look, do we really need to decouple update_and_free_page and enqueue_huge_page? These two functions do not handle the lock, but rather the functions that call them (as would be in our case). Only update_and_free_page drops the lock during the freeing of a gigantic page and then it takes it again, as the caller is who took the lock. am I missing anything obvious here? -- Oscar Salvador SUSE L3