linux-kernel - Re: [PATCH RFC 2/7] md/raid0: convert raid0_handle_discard() to use bio_submit

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Message-ID: <aK1oLSppbXNELKCX@infradead.org>
Date: Tue, 26 Aug 2025 00:54:21 -0700
From: Christoph Hellwig <hch@...radead.org>
To: Yu Kuai <yukuai1@...weicloud.com>
Cc: Christoph Hellwig <hch@...radead.org>, colyli@...nel.org, hare@...e.de,
	tieren@...as.com, axboe@...nel.dk, tj@...nel.org,
	josef@...icpanda.com, song@...nel.org, akpm@...ux-foundation.org,
	neil@...wn.name, linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
	linux-raid@...r.kernel.org, yi.zhang@...wei.com,
	yangerkun@...wei.com, johnny.chenyi@...wei.com,
	"yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH RFC 2/7] md/raid0: convert raid0_handle_discard() to use
 bio_submit_split()

On Tue, Aug 26, 2025 at 09:08:33AM +0800, Yu Kuai wrote:
> 在 2025/08/25 18:57, Christoph Hellwig 写道:
> > On Mon, Aug 25, 2025 at 05:36:55PM +0800, Yu Kuai wrote:
> > > +		bio = bio_submit_split(bio,
> > > +				zone->zone_end - bio->bi_iter.bi_sector,
> > > +				&mddev->bio_set);
> > 
> > Do you know why raid0 and linear use mddev->bio_set for splitting
> > instead of their own split bio_sets like raid1/10/5?  Is this safe?
> > 
> 
> I think it's not safe, as mddev->bio_split pool size is just 2, reuse
> this pool to split multiple times before submitting will need greate
> pool size to make this work.
> 
> By the way, do you think it's better to increate disk->bio_split pool
> size to 4 and convert all mdraid internal split to use disk->bio_split
> directly?

I don't really know where that magic number 4 or even the current number
comes from, but I think Jens might be amenable to a small increase with a
good explanation.