Dan Carpenter <dan.carpenter@xxxxxxxxxx> writes: > On Tue, Jun 02, 2020 at 09:23:57PM +1000, Michael Ellerman wrote: >> Markus Elfring <Markus.Elfring@xxxxxx> 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@xxxxxxxxxxxxxxxxxxxxx/ >> >>> https://lore.kernel.org/linuxppc-dev/00845261-8528-d011-d3b8-e9355a231d3a@xxxxxxxxxxxxxxxxxxxxx/ >> >>> 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. I see ~175 defconfigs with CONFIG_EXPERT=y, so that's not really a high bar unfortunately. And there's 38 defconfigs with SLUB_DEBUG=n. So for kernels built with those defconfigs that documentation is plain wrong and misleading. And then there's SLOB which doesn't dump stack anywhere AFAICS. In fact slab_out_of_memory() doesn't emit a stack dump either, it just prints a bunch of slab related info! > 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. I agree that in many cases those printks are just a waste of space in the source and the binary and should be removed. But I dislike being told "these generic allocation functions all emit a stack dump" only to find out that actually they don't, they print some other debug info, and depending on config settings they actually don't print _anything_. cheers
