Re: [V9fs-developer] [PATCH 5/6] 9p: Use a slab for allocating requests

From: Dominique Martinet <asmadeus@codewreck.org>
To: Matthew Wilcox <willy@infradead.org>
Cc: v9fs-developer@lists.sourceforge.net,
	Latchesar Ionkov <lucho@ionkov.net>,
	Eric Van Hensbergen <ericvh@gmail.com>,
	linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	Ron Minnich <rminnich@sandia.gov>
Subject: Re: [V9fs-developer] [PATCH 5/6] 9p: Use a slab for allocating requests
Date: Wed, 11 Jul 2018 16:24:57 +0200	[thread overview]
Message-ID: <20180711142457.GB9691@nautica> (raw)
In-Reply-To: <20180711141256.GC23640@bombadil.infradead.org>

Matthew Wilcox wrote on Wed, Jul 11, 2018:
> On Wed, Jul 11, 2018 at 03:33:13PM +0200, Dominique Martinet wrote:
> > Well this appears to work but P9_NOTAG being '(u16)(~0)' I'm not too
> > confident with P9_NOTAG + 1. . . it doesn't look like it's overflowing
> > before the cast on my laptop but is that guaranteed?
> 
> By my understanding of n1256.pdf ... this falls under 6.3.1.8 ("Usual
> arithmetic conversions").  We have a u16 and an int.  Therefore this
> rule applies:
> 
>     Otherwise, if the type of the operand with signed integer type can
>     represent all of the values of the type of the operand with unsigned
>     integer type, then the operand with unsigned integer type is converted
>     to the type of the operand with signed integer type.

Thanks for checking, that'll work then.

> > I do not see any call to idr_destroy, is that OK?
> 
> Yes, that's fine.  It used to be (back in 2013) that one had to call
> idr_destroy() in order to free the preallocated idr data structures.
> Now it's a no-op if called on an empty IDR, and I would expect that both
> IDRs are empty at the time that it comes to unloading the module (and if
> they aren't, we probably have bigger problems than a small memory leak).
> Some users like to assert that the IDR is empty; most do not go to that
> extent of defensive programming.

Ok, I agree we're not there yet.

Just comments nitpicks, then :)

-- 
Dominique Martinet