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Date: Tue, 27 Jan 2026 07:53:18 +0100
From: Christoph Hellwig <hch@lst.de>
To: Keith Busch <kbusch@kernel.org>
Cc: Chris Mason <clm@meta.com>, Christoph Hellwig <hch@lst.de>,
	Jens Axboe <axboe@kernel.dk>, Carlos Maiolino <cem@kernel.org>,
	Damien Le Moal <dlemoal@kernel.org>,
	Hans Holmberg <hans.holmberg@wdc.com>, linux-block@vger.kernel.org,
	linux-xfs@vger.kernel.org, Carlos Maiolino <cmaiolino@redhat.com>
Subject: Re: [PATCH 3/3] xfs: rework zone GC buffer management
Message-ID: <20260127065318.GA26234@lst.de>
References: <20260114130651.3439765-4-hch@lst.de> <20260125000314.561545-1-clm@meta.com> <aXfO_ghd0yoKK8dm@kbusch-mbp>
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On Mon, Jan 26, 2026 at 01:30:54PM -0700, Keith Busch wrote:
> I think you're right that ring wrap can't distinguish full vs. empty here.
>  
> > A common solution is to track a separate count, or to sacrifice one slot
> > so head == tail always means empty, and head == tail-1 means full.
> 
> The buffer size is a power of two, so I suggest just let scratch_head
> and scratch_tail only increment without modulo, and rely on the unsigned
> int wrapping. We can get the actual offset by masking the head with the
> scratch size.

I actually added a available tracking member yesterday.  It turns out
this simplified the code quite a bit, but so does your version.  I've
kicked off QA on it, which I'd have to redo for this version.

https://git.infradead.org/?p=users/hch/xfs.git;a=shortlog;h=refs/heads/xfs-zoned-fixes