linux-kernel - Re: [PATCH -next RFC 2/6] block: refactor to split bio thoroughly

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Date:   Tue, 29 Mar 2022 08:35:29 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Christoph Hellwig <hch@...radead.org>, Yu Kuai <yukuai3@...wei.com>
Cc:     andriy.shevchenko@...ux.intel.com, john.garry@...wei.com,
        ming.lei@...hat.com, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, yi.zhang@...wei.com
Subject: Re: [PATCH -next RFC 2/6] block: refactor to split bio thoroughly

On 3/29/22 7:32 AM, Christoph Hellwig wrote:
> On Tue, Mar 29, 2022 at 05:40:44PM +0800, Yu Kuai wrote:
>> Currently, the splited bio is handled first, and then continue to split
>> the original bio. This patch tries to split the original bio thoroughly,
>> so that it can be known in advance how many tags will be needed.
> 
> How do you avoid the deadlock risk with all the split bios being
> submitted together?

That too

> But more importantly why does your use case even have splits that get
> submitted together?  Is this a case of Linus' stupidly low default
> max_sectors when the hardware supports more, or is the hardware limited
> to a low number of sectors per request?  Or do we hit another reason
> for the split?

See the posted use case, it's running 512kb ios on a 128kb device.

-- 
Jens Axboe