linux-kernel - Re: [PATCH v3 22/25] cxl/region: Read existing extents on region creation

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Message-ID: <66c8ffc8985ea_a4ea22949a@iweiny-mobl.notmuch>
Date: Fri, 23 Aug 2024 16:31:52 -0500
From: Ira Weiny <ira.weiny@...el.com>
To: Dave Jiang <dave.jiang@...el.com>, <ira.weiny@...el.com>, Fan Ni
	<fan.ni@...sung.com>, Jonathan Cameron <Jonathan.Cameron@...wei.com>,
	"Navneet Singh" <navneet.singh@...el.com>, Chris Mason <clm@...com>, Josef
 Bacik <josef@...icpanda.com>, David Sterba <dsterba@...e.com>, Petr Mladek
	<pmladek@...e.com>, Steven Rostedt <rostedt@...dmis.org>, Andy Shevchenko
	<andriy.shevchenko@...ux.intel.com>, Rasmus Villemoes
	<linux@...musvillemoes.dk>, Sergey Senozhatsky <senozhatsky@...omium.org>,
	Jonathan Corbet <corbet@....net>, Andrew Morton <akpm@...ux-foundation.org>
CC: 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>,
	<linux-doc@...r.kernel.org>, <nvdimm@...ts.linux.dev>
Subject: Re: [PATCH v3 22/25] cxl/region: Read existing extents on region
 creation

Dave Jiang wrote:
> 
> 
> On 8/16/24 7:44 AM, ira.weiny@...el.com wrote:
> > From: Navneet Singh <navneet.singh@...el.com>
> > 
> > Dynamic capacity device extents may be left in an accepted state on a
> > device due to an unexpected host crash.  In this case it is expected
> > that the creation of a new region on top of a DC partition can read
> > those extents and surface them for continued use.
> > 
> > Once all endpoint decoders are part of a region and the region is being
> > realized a read of the devices extent list can reveal these previously
> > accepted extents.
> 
> Once all endpoint decoders are part of a region and the region is being
> realized, a read of the 'devices extend list' can reveal these previously
> accepted extents.
> 

Thanks, done.

[snip]

> > +
> > +/**
> > + * cxl_read_extent_list() - Read existing extents
> > + * @cxled: Endpoint decoder which is part of a region
> > + *
> > + * Issue the Get Dynamic Capacity Extent List command to the device
> > + * and add existing extents if found.
> > + */
> > +void cxl_read_extent_list(struct cxl_endpoint_decoder *cxled)
> 
> cxl_process_extend_list()? It seems to do read+validate+add. 

yea maybe.  The name of this function actually changed in my mind many
times.  In the end I went for the higher level meaning which was to read
the existing extent list.

I'll change it because I'm not convinced of any particular name.

> 
> > +{
> > +	int retry = 10;
> 
> arbitrary retry number? maybe define it?

Sure.  But it is still an arbitrary value of 10.

I'll document my justification thusly.

/*
   ...
 * A retry of 10 is somewhat arbitrary, however, extent changes should be      
 * relatively rare while bringing up a region.  So 10 should be plenty.        
 */                                                                            
#define CXL_READ_EXTENT_LIST_RETRY 10

Ira


[snip]