linux-kernel - Re: [HPDD-discuss] [PATCH] staging: lustre: llite: Use kzalloc and rewrite null tests

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Date:	Fri, 19 Sep 2014 13:36:24 +0000
From:	"Drokin, Oleg" <oleg.drokin@...el.com>
To:	Julia Lawall <julia.lawall@...6.fr>
CC:	Dan Carpenter <dan.carpenter@...cle.com>,
	"<devel@...verdev.osuosl.org>" <devel@...verdev.osuosl.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"<kernel-janitors@...r.kernel.org>" <kernel-janitors@...r.kernel.org>,
	"<linux-kernel@...r.kernel.org>" <linux-kernel@...r.kernel.org>,
	"<HPDD-discuss@...1.01.org>" <HPDD-discuss@...1.01.org>
Subject: Re: [HPDD-discuss] [PATCH] staging: lustre: llite: Use kzalloc and
 rewrite null tests

Hello!

   First, thanks for your patches and efforts spent on these cleanups.

On Sep 19, 2014, at 12:45 AM, Julia Lawall wrote:

> With respect to the upper case lower case issue, does the thing need to be
> a macro?  I think that the lowercase is more or less fine, but only if
> what is behind it is a function.

I don't have a strong opinion either way as long as we have all the functionality
we need.

> I say more or less fine, because normally in the kernel the special
> allocators have special purposes, eg allocating and initializing the xyz
> structure.  Here what is wanted is a general purpose allocator with lots
> of special tracing features, so it is not quite the same thing.  And one
> can wonder why all of these special tracing features are not relevant to
> the kernel as a whole?

Like I explained in my previous email, many of the tracing features are already
possible to replace with other existing in-kernel mechanisms like kmemleak.

Except the total tally of allocations/frees so that a memleak could be visibly
easily seen on module unload time. I think this would be useful for other
kinds of modules too, not just lustre, so having that as a generic allocator
feature would be cool too.

> In reading through the description of the needed features, it seems like
> only the _ptr extension requires being a macro.  Do we need that?  The

We only need that as a less error-prone way of having
x = obd_kzalloc(sizeof(*x), ….)
…
obd_free(…, sizeof(*x))

Real free function does not take size argument, but we need that for
total allocated/freed accounting. Easy to have disconnect with
the size argument of obd_free to be wrong.

> rest of the kernel manages to do x = kzalloc(sizeof(*x),...) ok.  It's
> unpleasant to have an assignment hidden in this way.  And currently it is
> not used consistently.  There are some OBD_ALLOCs that have the same form.

Yes, those are converted as thy are noticed.

> Sorry for overlooking the frees.  I was focusing on trying one thing at a
> time...

I kind of think it's a related issue.
Touching ones needs to touch the other if not in the same patch then in
a next patch. And that's why I think consideations for what FREEs would need
is needed from the start, so the FREEs removal patch does not goes and patches a bunch of just patched allocs.

Thanks.

Bye,
    Oleg--
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