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Date: Thu, 15 Jan 2026 07:12:52 +0100
From: Christoph Hellwig <hch@lst.de>
To: "Darrick J. Wong" <djwong@kernel.org>
Cc: 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>,
	Keith Busch <kbusch@kernel.org>, 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: <20260115061252.GB9205@lst.de>
References: <20260114130651.3439765-1-hch@lst.de> <20260114130651.3439765-4-hch@lst.de> <20260114195947.GI15551@frogsfrogsfrogs>
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On Wed, Jan 14, 2026 at 11:59:47AM -0800, Darrick J. Wong wrote:
> > Signed-off-by: Christoph Hellwig <hch@lst.de>
> > Reviewed-by: Hans Holmberg <hans.holmberg@wdc.com>
> > Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com>
> > Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
> 
> Huh.  I guess I never touched this patch at all???

Not yet :)

> Ok so it looks like we're switching out garbage collecting with two
> independent (but not) scratchpads for what amounts to a ring buffer
> consisting of a bunch of discontig folios.

Yeah.

> Now when gc wants to move some data, we compute the number of folios we
> need, and bump scratch_head by that amount.  Then we attach those folios
> to a read bio and submit it.  When that finishes, we call bio_reuse with
> REQ_OP_WRITE and submit that.  When the write finishes we do the "remap
> if mapping hasn't changed" dance to update the metadata, and advance the
> tail by however many folios we've stopped using.
> 
> If I got that right, then

You did, thanks!