Re: [PATCH] mm, page_alloc: warn about empty nodemask

[Vlastimil Babka <vbabka@suse.cz>]

On 09/09/2016 06:03 AM, Li Zhong wrote:
>
>>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>>> index a2214c6..d624ff3 100644
>>> --- a/mm/page_alloc.c
>>> +++ b/mm/page_alloc.c
>>> @@ -3448,6 +3448,12 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
>>> 	if (page)
>>> 		goto got_pg;
>>>
>>> +	if (ac->nodemask && nodes_empty(*ac->nodemask)) {
>>> +		pr_warn("nodemask is empty\n");
>>> +		gfp_mask &= ~__GFP_NOWARN;
>>> +		goto nopage;
>>> +	}
>>> +
>>
>> Wouldn't it be better to do
>>
>> 	if (WARN_ON(ac->nodemask && nodes_empty(*ac->nodemask)) {
>> 		...
>>
>> so we can identify the misbehaving call site?
>
> I think with __GFP_NOWARN cleared, we could know the call site from warn_alloc_failed().
> And the message a??nodemask is emptya?? makes the error obvious without going to the source.

Yes, that was my suggestion. It uses the generic warn_alloc_failed() this way. 
With a WARN_ON we would either have to "return NULL" (and get only the WARN_ON 
without the extra warn_alloc_failed() stuff) or "goto nopage" and thus get two 
backtraces. But this should be really rare occurence, so I don't have a 
particularly strong preference.

Anyway, since I suggested it in the first place:
Acked-by: Vlastimil Babka <vbabka@suse.cz>

> Thanks, Zhong
>

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