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=-16.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT 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 DDE33C433B4 for ; Sat, 10 Apr 2021 07:24:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BB2DF6115B for ; Sat, 10 Apr 2021 07:24:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234529AbhDJHZJ (ORCPT ); Sat, 10 Apr 2021 03:25:09 -0400 Received: from szxga07-in.huawei.com ([45.249.212.35]:17306 "EHLO szxga07-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234432AbhDJHZD (ORCPT ); Sat, 10 Apr 2021 03:25:03 -0400 Received: from DGGEMS410-HUB.china.huawei.com (unknown [172.30.72.60]) by szxga07-in.huawei.com (SkyGuard) with ESMTP id 4FHRKQ2fRDz9xRP; Sat, 10 Apr 2021 15:22:34 +0800 (CST) Received: from huawei.com (10.175.104.175) by DGGEMS410-HUB.china.huawei.com (10.3.19.210) with Microsoft SMTP Server id 14.3.498.0; Sat, 10 Apr 2021 15:24:37 +0800 From: Miaohe Lin To: , CC: , , , Subject: [PATCH v2 3/5] mm/hugeltb: clarify (chg - freed) won't go negative in hugetlb_unreserve_pages() Date: Sat, 10 Apr 2021 03:23:46 -0400 Message-ID: <20210410072348.20437-4-linmiaohe@huawei.com> X-Mailer: git-send-email 2.19.1 In-Reply-To: <20210410072348.20437-1-linmiaohe@huawei.com> References: <20210410072348.20437-1-linmiaohe@huawei.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7BIT Content-Type: text/plain; charset=US-ASCII X-Originating-IP: [10.175.104.175] X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The resv_map could be NULL since this routine can be called in the evict inode path for all hugetlbfs inodes and we will have chg = 0 in this case. But (chg - freed) won't go negative as Mike pointed out: "If resv_map is NULL, then no hugetlb pages can be allocated/associated with the file. As a result, remove_inode_hugepages will never find any huge pages associated with the inode and the passed value 'freed' will always be zero." Add a comment clarifying this to make it clear and also avoid confusion. Signed-off-by: Miaohe Lin --- mm/hugetlb.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 9b4c05699a90..387c9a62615e 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -5435,6 +5435,9 @@ long hugetlb_unreserve_pages(struct inode *inode, long start, long end, /* * If the subpool has a minimum size, the number of global * reservations to be released may be adjusted. + * + * Note that !resv_map implies freed == 0. So (chg - freed) + * won't go negative. */ gbl_reserve = hugepage_subpool_put_pages(spool, (chg - freed)); hugetlb_acct_memory(h, -gbl_reserve); -- 2.19.1