linux-kernel - Re: [HPDD-discuss] [PATCH] nfsd: add a new EXPORT_OP_NOWCC flag to struct export

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Message-ID: <20150916180424.47915fed@synchrony.poochiereds.net>
Date:	Wed, 16 Sep 2015 18:04:24 -0400
From:	Jeff Layton <jlayton@...chiereds.net>
To:	"bfields@...ldses.org" <bfields@...ldses.org>
Cc:	"Dilger, Andreas" <andreas.dilger@...el.com>,
	"cluster-devel@...hat.com" <cluster-devel@...hat.com>,
	"linux-nfs@...r.kernel.org" <linux-nfs@...r.kernel.org>,
	"fuse-devel@...ts.sourceforge.net" <fuse-devel@...ts.sourceforge.net>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"HPDD-discuss@...ts.01.org" <HPDD-discuss@...ts.01.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"ceph-devel@...r.kernel.org" <ceph-devel@...r.kernel.org>,
	"ocfs2-devel@....oracle.com" <ocfs2-devel@....oracle.com>
Subject: Re: [HPDD-discuss] [PATCH] nfsd: add a new EXPORT_OP_NOWCC flag to
 struct export_operations

On Wed, 16 Sep 2015 17:30:44 -0400
"bfields@...ldses.org" <bfields@...ldses.org> wrote:

> On Wed, Sep 16, 2015 at 01:18:29PM -0400, Jeff Layton wrote:
> > On Mon, 14 Sep 2015 12:10:15 -0400
> > "bfields@...ldses.org" <bfields@...ldses.org> wrote:
> > 
> > > On Sat, Sep 12, 2015 at 06:24:54AM -0400, Jeff Layton wrote:
> > > > I don't think it matters, at least not on x86_64. bools and chars both
> > > > require a byte. pahole does show this adding a new hole, but that's
> > > > just because this brings the code up to 5 flags and the next field
> > > > (fh_pre_size) needs to be aligned.
> > > > 
> > > > I do agree that replacing those other unsigned chars with bools is more
> > > > clear however. Maybe we should even replace them all with a single
> > > > unsigned int and use bitops to set flags in there. That would be more
> > > > space efficient now that we're at 5 flags.
> > > 
> > > Makes sense to me.--b.
> > 
> > I played around with this a little today, and it turns out not to make
> > a lot of difference. Here's what pahole says about the existing code
> > (once I moved fh_maxsize to snuggle up to fh_handle to plug a hole):
> ...
> > I used an unsigned long for fh_flags since we might as well. Making it
> > smaller just adds a hole in there since the compiler wants to align the
> > fh_pre_size. Moving it around doesn't help either as it just moves the
> > hole around. Note that this is x86_64. It might look different on a
> > 32-bit arch, but I doubt it really matters much in the big scheme of
> > things.
> > 
> > Bruce, I'll send out the patches that change this if you like, but I'm
> > inclined to just leave this alone since it doesn't seem to have a
> > tangible benefit.
> 
> Unless more flags are imminent I guess it's just a question of which is
> more readable.  Arguably there's some value to making it more obvious
> that these are each just a bit.  I'll accept your judgement on that
> question.
> 
> --b.

Sure. Maybe we just switch them to bools. It's the same space
utilization but it does make things a little more clear.

-- 
Jeff Layton <jlayton@...chiereds.net>
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