linux-kernel - Re: [RESEND,v5,1/2] bio: limit bio max size

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

Date:   Sun, 11 Apr 2021 22:13:01 +0000
From:   Damien Le Moal <Damien.LeMoal@....com>
To:     Bart Van Assche <bvanassche@....org>,
        Changheun Lee <nanich.lee@...sung.com>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
CC:     Johannes Thumshirn <Johannes.Thumshirn@....com>,
        "asml.silence@...il.com" <asml.silence@...il.com>,
        "axboe@...nel.dk" <axboe@...nel.dk>,
        "hch@...radead.org" <hch@...radead.org>,
        "jisoo2146.oh@...sung.com" <jisoo2146.oh@...sung.com>,
        "junho89.kim@...sung.com" <junho89.kim@...sung.com>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "ming.lei@...hat.com" <ming.lei@...hat.com>,
        "mj0123.lee@...sung.com" <mj0123.lee@...sung.com>,
        "osandov@...com" <osandov@...com>,
        "patchwork-bot@...nel.org" <patchwork-bot@...nel.org>,
        "seunghwan.hyun@...sung.com" <seunghwan.hyun@...sung.com>,
        "sookwan7.kim@...sung.com" <sookwan7.kim@...sung.com>,
        "tj@...nel.org" <tj@...nel.org>,
        "tom.leiming@...il.com" <tom.leiming@...il.com>,
        "woosung2.lee@...sung.com" <woosung2.lee@...sung.com>,
        "yt0928.kim@...sung.com" <yt0928.kim@...sung.com>
Subject: Re: [RESEND,v5,1/2] bio: limit bio max size

On 2021/04/09 23:47, Bart Van Assche wrote:
> On 4/7/21 3:27 AM, Damien Le Moal wrote:
>> On 2021/04/07 18:46, Changheun Lee wrote:
>>> I'll prepare new patch as you recommand. It will be added setting of
>>> limit_bio_size automatically when queue max sectors is determined.
>>
>> Please do that in the driver for the HW that benefits from it. Do not do this
>> for all block devices.
> 
> Hmm ... is it ever useful to build a bio with a size that exceeds 
> max_hw_sectors when submitting a bio directly to a block device, or in 
> other words, if no stacked block driver sits between the submitter and 
> the block device? Am I perhaps missing something?

Device performance wise, the benefits are certainly not obvious to me either.
But for very fast block devices, I think the CPU overhead of building more
smaller BIOs may be significant compared to splitting a large BIO into multiple
requests. Though it may be good to revisit this with some benchmark numbers.

> 
> Thanks,
> 
> Bart.
> 


-- 
Damien Le Moal
Western Digital Research