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

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Date:   Tue, 2 Jun 2020 14:41:58 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Michael Ellerman <mpe@...erman.id.au>
Cc:     Markus Elfring <Markus.Elfring@....de>,
        Liao Pingfang <liao.pingfang@....com.cn>,
        linuxppc-dev@...ts.ozlabs.org, Joe Perches <joe@...ches.com>,
        Allison Randal <allison@...utok.net>,
        Anton Vorontsov <anton@...msg.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Colin Cross <ccross@...roid.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kees Cook <keescook@...omium.org>,
        Paul Mackerras <paulus@...ba.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tony Luck <tony.luck@...el.com>,
        Wang Liang <wang.liang82@....com.cn>,
        Xue Zhihong <xue.zhihong@....com.cn>,
        Yi Wang <wang.yi59@....com.cn>,
        LKML <linux-kernel@...r.kernel.org>,
        kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] powerpc/nvram: Replace kmalloc with kzalloc in the error
 message

On Tue, Jun 02, 2020 at 09:23:57PM +1000, Michael Ellerman wrote:
> Markus Elfring <Markus.Elfring@....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