Re: [PATCH] powerpc/nvram: Replace kmalloc with kzalloc in the error message

From: Dan Carpenter <dan.carpenter@oracle.com>
To: Michael Ellerman <mpe@ellerman.id.au>
Cc: Markus Elfring <Markus.Elfring@web.de>,
	Liao Pingfang <liao.pingfang@zte.com.cn>,
	linuxppc-dev@lists.ozlabs.org, Joe Perches <joe@perches.com>,
	Allison Randal <allison@lohutok.net>,
	Anton Vorontsov <anton@enomsg.org>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Colin Cross <ccross@android.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Kees Cook <keescook@chromium.org>,
	Paul Mackerras <paulus@samba.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Tony Luck <tony.luck@intel.com>,
	Wang Liang <wang.liang82@zte.com.cn>,
	Xue Zhihong <xue.zhihong@zte.com.cn>,
	Yi Wang <wang.yi59@zte.com.cn>,
	LKML <linux-kernel@vger.kernel.org>,
	kernel-janitors@vger.kernel.org
Subject: Re: [PATCH] powerpc/nvram: Replace kmalloc with kzalloc in the error message
Date: Tue, 2 Jun 2020 14:41:58 +0300	[thread overview]
Message-ID: <20200602114158.GB30374@kadam> (raw)
In-Reply-To: <87a71liucy.fsf@mpe.ellerman.id.au>

On Tue, Jun 02, 2020 at 09:23:57PM +1000, Michael Ellerman wrote:
> Markus Elfring <Markus.Elfring@web.de> writes:
> >>>> Please just remove the message instead, it's a tiny allocation that's
> >>>> unlikely to ever fail, and the caller will print an error anyway.
> >>>
> >>> How do you think about to take another look at a previous update suggestion
> >>> like the following?
> >>>
> >>> powerpc/nvram: Delete three error messages for a failed memory allocation
> >>> https://patchwork.ozlabs.org/project/linuxppc-dev/patch/00845261-8528-d011-d3b8-e9355a231d3a@users.sourceforge.net/
> >>> https://lore.kernel.org/linuxppc-dev/00845261-8528-d011-d3b8-e9355a231d3a@users.sourceforge.net/
> >>> https://lore.kernel.org/patchwork/patch/752720/
> >>> https://lkml.org/lkml/2017/1/19/537
> >>
> >> That deleted the messages from nvram_scan_partitions(), but neither of
> >> the callers of nvram_scan_paritions() check its return value or print
> >> anything if it fails. So removing those messages would make those
> >> failures silent which is not what we want.
> >
> > * How do you think about information like the following?
> >   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/coding-style.rst?id=f359287765c04711ff54fbd11645271d8e5ff763#n883
> > “…
> > These generic allocation functions all emit a stack dump on failure when used
> > without __GFP_NOWARN so there is no use in emitting an additional failure
> > message when NULL is returned.
> > …”
> 
> Are you sure that's actually true?
> 
> A quick look around in slub.c leads me to:
> 
> slab_out_of_memory(struct kmem_cache *s, gfp_t gfpflags, int nid)
> {
> #ifdef CONFIG_SLUB_DEBUG

You first have to enable EXPERT mode before you can disable SLUB_DEBUG.
So that hopefully means you *really* want to save memory.  It doesn't
make sense to add a bunch of memory wasting printks when the users want
to go to extra lengths to conserve memory.

regards,
dan carpenter