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 53B08C433EF for ; Tue, 10 May 2022 02:21:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234582AbiEJCZX (ORCPT ); Mon, 9 May 2022 22:25:23 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39546 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231676AbiEJCZU (ORCPT ); Mon, 9 May 2022 22:25:20 -0400 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D94BC590BB for ; Mon, 9 May 2022 19:21:24 -0700 (PDT) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.54]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4Ky1x33jL3zhYym; Tue, 10 May 2022 10:20:55 +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 15.1.2375.24; Tue, 10 May 2022 10:21:21 +0800 Subject: Re: [PATCH 09/15] mm/swap: avoid calling swp_swap_info when try to check SWP_STABLE_WRITES To: NeilBrown CC: , , , , , , , , , , References: <20220509131416.17553-1-linmiaohe@huawei.com> <20220509131416.17553-10-linmiaohe@huawei.com> <165214248406.14782.6536817483979050668@noble.neil.brown.name> From: Miaohe Lin Message-ID: Date: Tue, 10 May 2022 10:21:21 +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: <165214248406.14782.6536817483979050668@noble.neil.brown.name> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.177.76] X-ClientProxiedBy: dggems705-chm.china.huawei.com (10.3.19.182) 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 2022/5/10 8:28, NeilBrown wrote: > On Mon, 09 May 2022, Miaohe Lin wrote: >> Use flags of si directly to check SWP_STABLE_WRITES to avoid possible >> READ_ONCE and thus save some cpu cycles. >> >> Signed-off-by: Miaohe Lin >> --- >> mm/memory.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/mm/memory.c b/mm/memory.c >> index 9c3e7e6ac202..89dd15504f3d 100644 >> --- a/mm/memory.c >> +++ b/mm/memory.c >> @@ -3892,7 +3892,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) >> */ >> exclusive = true; >> } else if (exclusive && PageWriteback(page) && >> - (swp_swap_info(entry)->flags & SWP_STABLE_WRITES)) { >> + (si->flags & SWP_STABLE_WRITES)) { > > Should this have a data_race() annotation. Other bit-tests of si->flags > do because scan_swap_map_slots can update it asynchronously, but we know > that won't matter in practice. Yes, you're right. scan_swap_map_slots can update si->flags asynchronously while do_swap_page tests SWP_STABLE_WRITES here. We know this is harmless because SWP_STABLE_WRITES is only changed at swapon/swapoff. Will add data_race() annotation in next version to avoid possible KCSAN data-race complaint. Many thanks for pointing this out! :) > > Thanks, > NeilBrown > > >> /* >> * This is tricky: not all swap backends support >> * concurrent page modifications while under writeback. >> -- >> 2.23.0 >> >> > . >