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=-4.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_PASS,UNPARSEABLE_RELAY 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 B7622C43387 for ; Wed, 19 Dec 2018 18:41:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8D9B5217D7 for ; Wed, 19 Dec 2018 18:41:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729913AbeLSSlq (ORCPT ); Wed, 19 Dec 2018 13:41:46 -0500 Received: from out30-130.freemail.mail.aliyun.com ([115.124.30.130]:38729 "EHLO out30-130.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728017AbeLSSlq (ORCPT ); Wed, 19 Dec 2018 13:41:46 -0500 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R171e4;CH=green;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01f04392;MF=yang.shi@linux.alibaba.com;NM=1;PH=DS;RN=7;SR=0;TI=SMTPD_---0TGA15lD_1545244817; Received: from US-143344MP.local(mailfrom:yang.shi@linux.alibaba.com fp:SMTPD_---0TGA15lD_1545244817) by smtp.aliyun-inc.com(127.0.0.1); Thu, 20 Dec 2018 02:40:19 +0800 Subject: Re: [RFC PATCH 1/2] mm: swap: check if swap backing device is congested or not To: Tim Chen , ying.huang@intel.com, tim.c.chen@intel.com, minchan@kernel.org, Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <1545115948-25467-1-git-send-email-yang.shi@linux.alibaba.com> <6a51d47a-b87f-b0f1-4dae-843730dba698@linux.intel.com> <03462367-3f75-4907-8c5e-526a919e5cf3@linux.alibaba.com> <606b73ed-da62-fdd1-71da-c4de7a02e837@linux.alibaba.com> From: Yang Shi Message-ID: <2df52dc3-ae66-0ab8-459e-49f49eaa569c@linux.alibaba.com> Date: Wed, 19 Dec 2018 10:40:16 -0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/19/18 9:28 AM, Tim Chen wrote: > On 12/18/18 9:56 PM, Yang Shi wrote: >> >> On 12/18/18 4:16 PM, Tim Chen wrote: >>> On 12/18/18 3:43 PM, Yang Shi wrote: >>>> On 12/18/18 11:29 AM, Tim Chen wrote: >>>>> On 12/17/18 10:52 PM, Yang Shi wrote: >>>>> >>>>>> diff --git a/mm/swap_state.c b/mm/swap_state.c >>>>>> index fd2f21e..7cc3c29 100644 >>>>>> --- a/mm/swap_state.c >>>>>> +++ b/mm/swap_state.c >>>>>> @@ -538,11 +538,15 @@ struct page *swap_cluster_readahead(swp_entry_t entry, gfp_t gfp_mask, >>>>>>        bool do_poll = true, page_allocated; >>>>>>        struct vm_area_struct *vma = vmf->vma; >>>>>>        unsigned long addr = vmf->address; >>>>>> +    struct inode *inode = si->swap_file->f_mapping->host; >>>>>>          mask = swapin_nr_pages(offset) - 1; >>>>>>        if (!mask) >>>>>>            goto skip; >>>>>> >>>>> Shmem will also be using this function and I don't think the inode_read_congested >>>>> logic is relevant for that case. >>>> IMHO, shmem is also relevant. As long as it is trying to readahead from swap, it should check if the underlying device is busy or not regardless of shmem or anon page. >>>> >>> I don't think your dereference inode = si->swap_file->f_mapping->host >>> is always safe.  You should do it only when (si->flags & SWP_FS) is true. >> Do you mean it is not safe for swap partition? > The f_mapping may not be instantiated. It is only done for SWP_FS. Really? I saw the below calls in swapon: swap_file = file_open_name(name, O_RDWR|O_LARGEFILE, 0); ... p->swap_file = swap_file; mapping = swap_file->f_mapping; inode = mapping->host; ... Then the below code manipulates the inode. And, trace shows file_open_name() does call blkdev_open if it is turning block device swap on. And, blkdev_open() would return instantiated address_space and inode. Am I missing something? Thanks, Yang > > Tim >