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Date: Wed, 10 Sep 2014 08:59:33 -0500 (CDT)
From: Christoph Lameter <cl@linux.com>
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To: Andrew Morton <akpm@linux-foundation.org>
cc: Jiri Kosina <jkosina@suse.cz>, Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, Dan Carpenter <dan.carpenter@oracle.com>,
        "Theodore Ts'o" <tytso@mit.edu>
Subject: Re: [PATCH] mm/sl[aou]b: make kfree() aware of error pointers
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Message-ID: <alpine.DEB.2.11.1409100858470.23359@gentwo.org>
References: <alpine.LNX.2.00.1409092319370.5523@pobox.suse.cz> <20140909162114.44b3e98cf925f125e84a8a06@linux-foundation.org>
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On Tue, 9 Sep 2014, Andrew Morton wrote:

> >
> > -	if (unlikely(ZERO_OR_NULL_PTR(objp)))
> > +	if (unlikely(ZERO_OR_NULL_PTR(objp) || IS_ERR(objp)))
> >  		return;
>
> kfree() is quite a hot path to which this will add overhead.  And we
> have (as far as we know) no code which will actually use this at
> present.

We could come up with a macro that does both. Basically if objp < 4086 or
so (signed comparison) then just return.