linux-kernel - Re: [PATCH 00/26] DCD: Add support for Dynamic Capacity Devices (DCD)

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Message-ID: <6604fe2dae8ea_2089029486@iweiny-mobl.notmuch>
Date: Wed, 27 Mar 2024 22:20:45 -0700
From: Ira Weiny <ira.weiny@...el.com>
To: fan <nifan.cxl@...il.com>, <ira.weiny@...el.com>
CC: Dave Jiang <dave.jiang@...el.com>, Fan Ni <fan.ni@...sung.com>, "Jonathan
 Cameron" <Jonathan.Cameron@...wei.com>, Navneet Singh
	<navneet.singh@...el.com>, Dan Williams <dan.j.williams@...el.com>, Davidlohr
 Bueso <dave@...olabs.net>, Alison Schofield <alison.schofield@...el.com>,
	Vishal Verma <vishal.l.verma@...el.com>, <linux-btrfs@...r.kernel.org>,
	<linux-cxl@...r.kernel.org>, <linux-kernel@...r.kernel.org>, Chris Mason
	<clm@...com>, Josef Bacik <josef@...icpanda.com>, David Sterba
	<dsterba@...e.com>
Subject: Re: [PATCH 00/26] DCD: Add support for Dynamic Capacity Devices (DCD)

fan wrote:
> On Sun, Mar 24, 2024 at 04:18:03PM -0700, ira.weiny@...el.com wrote:
> > A git tree of this series can be found here:

[snip]

> > 
> 
> Hi Ira,
> Have not got a chance to check the code yet, but I noticed one thing
> when testing with my DCD emulation code.
> Currently, if we do partial release, it seems the whole extent will be
> removed. Is it designed intentionally?
> 

Yes that is my intent.  I specifically called that out in patch 18.

https://lore.kernel.org/all/20240324-dcd-type2-upstream-v1-18-b7b00d623625@intel.com/

I thought we discussed this in one of the collaboration calls.  Mainly
this is to simplify by not attempting any split of the extents the host is
tracking.  It really is expected that the FM/device is going to keep those
extents offered and release them in their entirety.  I understand this may
complicate the device because it may see a release of memory prior to the
request of that release.  And perhaps this complicates the device.  But in
that case it (or the FM really) should not attempt to release partial
extents.

Ira

[snip]