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=-15.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 D9915C433ED for ; Wed, 7 Apr 2021 08:28:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AB27661074 for ; Wed, 7 Apr 2021 08:28:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241179AbhDGI2N (ORCPT ); Wed, 7 Apr 2021 04:28:13 -0400 Received: from mx2.suse.de ([195.135.220.15]:48698 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240739AbhDGI2E (ORCPT ); Wed, 7 Apr 2021 04:28:04 -0400 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 77DE9AFCF; Wed, 7 Apr 2021 08:27:53 +0000 (UTC) Date: Wed, 7 Apr 2021 10:27:49 +0200 From: Oscar Salvador To: Mike Kravetz Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Roman Gushchin , Michal Hocko , Shakeel Butt , David Hildenbrand , Muchun Song , David Rientjes , Miaohe Lin , Peter Zijlstra , Matthew Wilcox , HORIGUCHI NAOYA , "Aneesh Kumar K . V" , Waiman Long , Peter Xu , Mina Almasry , Hillf Danton , Joonsoo Kim , Barry Song , Will Deacon , Andrew Morton Subject: Re: [PATCH v4 5/8] hugetlb: call update_and_free_page without hugetlb_lock Message-ID: <20210407082744.GA10058@linux> References: <20210405230043.182734-1-mike.kravetz@oracle.com> <20210405230043.182734-6-mike.kravetz@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210405230043.182734-6-mike.kravetz@oracle.com> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Apr 05, 2021 at 04:00:40PM -0700, Mike Kravetz wrote: > With the introduction of remove_hugetlb_page(), there is no need for > update_and_free_page to hold the hugetlb lock. Change all callers to > drop the lock before calling. > > With additional code modifications, this will allow loops which decrease > the huge page pool to drop the hugetlb_lock with each page to reduce > long hold times. > > The ugly unlock/lock cycle in free_pool_huge_page will be removed in > a subsequent patch which restructures free_pool_huge_page. > > Signed-off-by: Mike Kravetz Without looking too close at the changes made to alloc_and_dissolve_huge_page(): Reviewed-by: Oscar Salvador One question below: > @@ -2671,22 +2682,34 @@ static void try_to_free_low(struct hstate *h, unsigned long count, > nodemask_t *nodes_allowed) > { > int i; > + struct page *page, *next; > + LIST_HEAD(page_list); > > if (hstate_is_gigantic(h)) > return; > > + /* > + * Collect pages to be freed on a list, and free after dropping lock > + */ > for_each_node_mask(i, *nodes_allowed) { > - struct page *page, *next; > struct list_head *freel = &h->hugepage_freelists[i]; > list_for_each_entry_safe(page, next, freel, lru) { > if (count >= h->nr_huge_pages) > - return; > + goto out; > if (PageHighMem(page)) > continue; > remove_hugetlb_page(h, page, false); > - update_and_free_page(h, page); > + list_add(&page->lru, &page_list); > } > } > + > +out: > + spin_unlock(&hugetlb_lock); > + list_for_each_entry_safe(page, next, &page_list, lru) { > + update_and_free_page(h, page); > + cond_resched(); > + } > + spin_lock(&hugetlb_lock); Can we get here with an empty list? Maybe if someone raced with us manipulating nr_huge_pages? AFAICS, this gets called under the lock, and the adjusting in remove_hugetlb_page() gets also done under the lock, so I guess this is not possible to happen. The reason I am asking is whether we want to check for the list to be empty before we do the unacquire/acquire lock dancing. -- Oscar Salvador SUSE L3