linux-ext4 - Re: Checking of NULL with __GFP

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Date:	Mon, 02 Mar 2009 00:35:21 -0700
From:	Andreas Dilger <adilger@....com>
To:	Manish Katiyar <mkatiyar@...il.com>
Cc:	ext4 <linux-ext4@...r.kernel.org>
Subject: Re: Checking of NULL with __GFP_NOFAIL in kzalloc()

On Mar 02, 2009  11:38 +0530, Manish Katiyar wrote:
> On Sun, Mar 1, 2009 at 11:35 AM, Manish Katiyar <mkatiyar@...il.com> wrote:
> > While going through jbd code, I was wondering why do we need to check
> > new_transaction for NULL, if we are passing __GFP_NOFAIL ?
> > Last code change around this code was when Ted converted kmalloc to
> > kzalloc, but since he also didn't remove it I am guessing there would
> > be some good reason for it. Can someone enlighten me ?
> 
> I didn't receive any response to this. So probably removing the NULL
> check is harmless. Or should I remove the __GFP_NOFAIL flag and keep
> the error handling ?

Neither, please.  The NULL check is harmless, and static code checkers
will complain about k[zm]alloc() without a corresponding NULL check.
Branch prediction will get this right, so the overhead is miniscule.

> > start_this_handle() {
> > ..........
> >        ..........
> >        new_transaction = kzalloc(sizeof(*new_transaction),
> >                        GFP_NOFS|__GFP_NOFAIL);
> >        if (!new_transaction) {
> >                ret = -ENOMEM;
> >                goto out;
> >        }
> >        ..........
> > }

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.

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