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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY 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 D510AC10F27 for ; Wed, 11 Mar 2020 01:17:22 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 1C40E20727 for ; Wed, 11 Mar 2020 01:17:22 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1C40E20727 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id BCDB06B0003; Tue, 10 Mar 2020 21:17:21 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id B7E306B0006; Tue, 10 Mar 2020 21:17:21 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id A6D656B0007; Tue, 10 Mar 2020 21:17:21 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0025.hostedemail.com [216.40.44.25]) by kanga.kvack.org (Postfix) with ESMTP id 905B46B0003 for ; Tue, 10 Mar 2020 21:17:21 -0400 (EDT) Received: from smtpin04.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 5A350180AD81D for ; Wed, 11 Mar 2020 01:17:21 +0000 (UTC) X-FDA: 76581318282.04.shoes84_4016798db8033 X-HE-Tag: shoes84_4016798db8033 X-Filterd-Recvd-Size: 4165 Received: from out30-54.freemail.mail.aliyun.com (out30-54.freemail.mail.aliyun.com [115.124.30.54]) by imf12.hostedemail.com (Postfix) with ESMTP for ; Wed, 11 Mar 2020 01:17:19 +0000 (UTC) X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R381e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04407;MF=richard.weiyang@linux.alibaba.com;NM=1;PH=DS;RN=6;SR=0;TI=SMTPD_---0TsFZ44m_1583889435; Received: from localhost(mailfrom:richard.weiyang@linux.alibaba.com fp:SMTPD_---0TsFZ44m_1583889435) by smtp.aliyun-inc.com(127.0.0.1); Wed, 11 Mar 2020 09:17:15 +0800 Date: Wed, 11 Mar 2020 09:17:15 +0800 From: Wei Yang To: Tim Chen Cc: Wei Yang , Andrew Morton , Wei Yang , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/swap_slots.c: don't reset the cache slot after use Message-ID: <20200311011715.GA47198@L-31X9LVDL-1304.local> Reply-To: Wei Yang References: <20200309090940.34130-1-richard.weiyang@linux.alibaba.com> <20200309174854.b6b8c7f019c3dde048c28f94@linux-foundation.org> <005f7454-16db-e8b5-dde2-8f2ddaa42932@linux.intel.com> <20200310222002.lr2vurqfk6jvfo2z@master> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Mar 10, 2020 at 04:03:07PM -0700, Tim Chen wrote: >On 3/10/20 3:20 PM, Wei Yang wrote: >> On Tue, Mar 10, 2020 at 11:13:13AM -0700, Tim Chen wrote: >>> On 3/9/20 5:48 PM, Andrew Morton wrote: >>>> On Mon, 9 Mar 2020 17:09:40 +0800 Wei Yang wrote: >>>> >>>>> Currently we would clear the cache slot if it is used. While this is not >>>>> necessary, since this entry would not be used until refilled. >>>>> >>>>> Leave it untouched and assigned the value directly to entry which makes >>>>> the code little more neat. >>>>> >>>>> Also this patch merges the else and if, since this is the only case we >>>>> refill and repeat swap cache. >>>> >>>> cc Tim, who can hopefully remember how this code works ;) >>>> >>>>> --- a/mm/swap_slots.c >>>>> +++ b/mm/swap_slots.c >>>>> @@ -309,7 +309,7 @@ int free_swap_slot(swp_entry_t entry) >>>>> >>>>> swp_entry_t get_swap_page(struct page *page) >>>>> { >>>>> - swp_entry_t entry, *pentry; >>>>> + swp_entry_t entry; >>>>> struct swap_slots_cache *cache; >>>>> >>>>> entry.val = 0; >>>>> @@ -336,13 +336,10 @@ swp_entry_t get_swap_page(struct page *page) >>>>> if (cache->slots) { >>>>> repeat: >>>>> if (cache->nr) { >>>>> - pentry = &cache->slots[cache->cur++]; >>>>> - entry = *pentry; >>>>> - pentry->val = 0; >>> >>> The cache entry was cleared after assignment for defensive programming, So there's >>> little chance I will be using a slot that has been assigned to someone else. >>> When I wrote swap_slots.c, this code was new and I want to make sure >>> that if something went wrong, and I assigned a swap slot that I shouldn't, >>> I will be able to detect quickly as I will only be stepping on entry 0. >>> >>> Otherwise such bug will be harder to detect as we will have two users of some random >>> swap slot stepping on each other. >>> >>> I'm okay if we want to get rid of this logic, now that the code has been >>> working correctly long enough. But I think is good hygiene to clear the >>> cached entry after it has been assigned. >>> >> >> This is fine to keep the logic, while I am wondering whether we need to do >> this through pointer. cache->slots[] contain the value, we can get and reset >> without pointer. >> >> The following code looks more obvious about the logic. >> >> entry = cache->slots[cache->cur]; >> cache->slots[cache->cur++].val = 0; > >Yes, this looks pretty good. Thanks, I would rephrase v2. > >Thanks. > >Tim -- Wei Yang Help you, Help me