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

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Date:   Wed, 11 Jul 2018 16:24:57 +0200
From:   Dominique Martinet <asmadeus@...ewreck.org>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     v9fs-developer@...ts.sourceforge.net,
        Latchesar Ionkov <lucho@...kov.net>,
        Eric Van Hensbergen <ericvh@...il.com>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Ron Minnich <rminnich@...dia.gov>
Subject: Re: [V9fs-developer] [PATCH 5/6] 9p: Use a slab for allocating
 requests

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