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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2B6C2C433EF for ; Thu, 17 Mar 2022 01:58:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1352563AbiCQB7P (ORCPT ); Wed, 16 Mar 2022 21:59:15 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57166 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232966AbiCQB7N (ORCPT ); Wed, 16 Mar 2022 21:59:13 -0400 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7EFC86428; Wed, 16 Mar 2022 18:57:57 -0700 (PDT) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.56]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4KJqsh64wnzcb5l; Thu, 17 Mar 2022 09:52:56 +0800 (CST) Received: from [10.174.177.76] (10.174.177.76) by canpemm500002.china.huawei.com (7.192.104.244) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2308.21; Thu, 17 Mar 2022 09:57:55 +0800 Subject: Re: [PATCH] hugetlb: do not demote poisoned hugetlb pages To: Mike Kravetz , , CC: HORIGUCHI NAOYA , Oscar Salvador , Michal Hocko , Andrew Morton , References: <20220307215707.50916-1-mike.kravetz@oracle.com> <6ba788b3-901e-d740-2575-bc652461187b@huawei.com> <8b40c33f-1bdf-2cda-5948-cf433302514e@oracle.com> From: Miaohe Lin Message-ID: Date: Thu, 17 Mar 2022 09:57:55 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: <8b40c33f-1bdf-2cda-5948-cf433302514e@oracle.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.177.76] X-ClientProxiedBy: dggems702-chm.china.huawei.com (10.3.19.179) To canpemm500002.china.huawei.com (7.192.104.244) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2022/3/17 6:31, Mike Kravetz wrote: > On 3/8/22 05:43, Miaohe Lin wrote: >> On 2022/3/8 5:57, Mike Kravetz wrote: >>> It is possible for poisoned hugetlb pages to reside on the free lists. >>> The huge page allocation routines which dequeue entries from the free >>> lists make a point of avoiding poisoned pages. There is no such check >>> and avoidance in the demote code path. >>> >>> If a hugetlb page on the is on a free list, poison will only be set in >>> the head page rather then the page with the actual error. If such a >>> page is demoted, then the poison flag may follow the wrong page. A page >>> without error could have poison set, and a page with poison could not >>> have the flag set. >>> >>> Check for poison before attempting to demote a hugetlb page. Also, >>> return -EBUSY to the caller if only poisoned pages are on the free list. >>> >>> Fixes: 8531fc6f52f5 ("hugetlb: add hugetlb demote page support") >>> Signed-off-by: Mike Kravetz >>> Cc: >>> --- >>> mm/hugetlb.c | 17 ++++++++++------- >>> 1 file changed, 10 insertions(+), 7 deletions(-) >>> >>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c >>> index b34f50156f7e..f8ca7cca3c1a 100644 >>> --- a/mm/hugetlb.c >>> +++ b/mm/hugetlb.c >>> @@ -3475,7 +3475,6 @@ static int demote_pool_huge_page(struct hstate *h, nodemask_t *nodes_allowed) >>> { >>> int nr_nodes, node; >>> struct page *page; >>> - int rc = 0; >>> >>> lockdep_assert_held(&hugetlb_lock); >>> >>> @@ -3486,15 +3485,19 @@ static int demote_pool_huge_page(struct hstate *h, nodemask_t *nodes_allowed) >>> } >>> >>> for_each_node_mask_to_free(h, nr_nodes, node, nodes_allowed) { >>> - if (!list_empty(&h->hugepage_freelists[node])) { >>> - page = list_entry(h->hugepage_freelists[node].next, >>> - struct page, lru); >>> - rc = demote_free_huge_page(h, page); >>> - break; >>> + list_for_each_entry(page, &h->hugepage_freelists[node], lru) { >>> + if (PageHWPoison(page)) >>> + continue; >>> + >>> + return demote_free_huge_page(h, page); >> >> It seems this patch is not ideal. Memory failure can hit the hugetlb page anytime without >> holding the hugetlb_lock. So the page might become HWPoison just after the check. But this >> patch should have handled the common case. Many thanks for your work. :) >> > > Correct, this patch handles the common case of not demoting a hugetlb > page if HWPoison is set. This is similar to code in the dequeue path > used when allocating a huge page for allocation use. > > As you point out, work still needs to be done to better coordinate > memory failure with demote as well as huge page freeing. As you know > Naoya is working on this now. It is unclear if that work will be limited > to memory error handling code, or if greater coordination with hugetlb > code will be required. > > Unless you have objections, I believe this patch should move forward and > be backported to stable trees. If we determine that more coordination > between memory error and hugetlb code is needed, that can be added later. I think this patch is good enough to move forward and be backported to stable trees. Many thanks. :) >