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

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Message-ID: <alpine.DEB.2.10.1409191546440.2525@hadrien>
Date:	Fri, 19 Sep 2014 15:50:01 +0200 (CEST)
From:	Julia Lawall <julia.lawall@...6.fr>
To:	"Drokin, Oleg" <oleg.drokin@...el.com>
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



On Fri, 19 Sep 2014, Drokin, Oleg wrote:

> 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.

Sure, it's fine.

Where do you want to go from here?  Should I propose function definitions
for obd_alloc and obd_free?  Could we leave the vmalloc issue for a future
set of changes?

julia