linux-kernel - Re: [PATCH] bcache: make stripe_size configurable and persistent for hardware raid5/6

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Message-ID: <yq1fspvshbw.fsf@ca-mkp.ca.oracle.com>
Date:   Mon, 10 Jan 2022 11:14:29 -0500
From:   "Martin K. Petersen" <martin.petersen@...cle.com>
To:     Eric Wheeler <bcache@...ts.ewheeler.net>
Cc:     Kent Overstreet <kent.overstreet@...il.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Coly Li <colyli@...e.de>, linux-block@...r.kernel.org,
        Jonathan Corbet <corbet@....net>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:BCACHE (BLOCK LAYER CACHE)" <linux-bcache@...r.kernel.org>
Subject: Re: [PATCH] bcache: make stripe_size configurable and persistent
 for hardware raid5/6


Eric,

> Ok so `git blame` shows that Kent added this to md/raid5.c in 
> c78afc6261b (Kent Overstreet 2013-07-11 22:39:53 -0700 7526)

Yep.

> Do you think we should leave the md-specific
> raid_partial_stripes_expensive setting and require users of RAID
> controllers to set the bit themselves in bcache---or---remove all
> raid_partial_stripes_expensive code and always treat writes as
> "expensive" when `opt_io` is defined?

I'd prefer the latter since that was the very intent of exporting the
device topology in an abstract and protocol-independent fashion.
However, I don't know enough about bcache internals to know whether it
is always the right choice, what the trade-offs are, etc.

-- 
Martin K. Petersen	Oracle Linux Engineering