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

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Date:   Tue, 29 Mar 2022 06:32:51 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Yu Kuai <yukuai3@...wei.com>
Cc:     axboe@...nel.dk, 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 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?

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?