linux-kernel - Re: [PATCH] readahead: Update the file_ra_state.ra

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <MW4PR84MB31450CAB2035C820B016E3F581A0A@MW4PR84MB3145.NAMPRD84.PROD.OUTLOOK.COM>
Date:   Tue, 31 Oct 2023 09:56:29 +0800
From:   Youling Tang <youling.tang@...look.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, tangyouling@...inos.cn
Subject: Re: [PATCH] readahead: Update the file_ra_state.ra_pages with each
 readahead operation

Hi, Matthew

On 2023/10/31 上午12:47, Matthew Wilcox wrote:
> On Mon, Oct 30, 2023 at 03:41:30PM +0800, Youling Tang wrote:
>> From: Youling Tang <tangyouling@...inos.cn>
>>
>> Changing the read_ahead_kb value midway through a sequential read of a
>> large file found that the ra->ra_pages value remained unchanged (new
>> ra_pages can only be detected the next time the file is opened). Because
>> file_ra_state_init() is only called once in do_dentry_open() in most
>> cases.
>>
>> In ondemand_readahead(), update bdi->ra_pages to ra->ra_pages to ensure
>> that the maximum pages that can be allocated by the readahead algorithm
>> are the same as (read_ahead_kb * 1024) / PAGE_SIZE after read_ahead_kb
>> is modified.
> Explain to me why this is the correct behaviour.
Because I initially expected to immediately improve the current read 
performance
by modifying read_ahead_kb when reading large files sequentially.
> Many things are only initialised at open() time and are not updated until
> the next open().  This is longstanding behaviour that some apps expect.
Thanks for your explanation. I will discard this change if the next open 
update is in line with the
apps expectation.

Thanks,
Youling.