Re: [PATCH 3/3] mm, page_alloc: reduce static keys in prep_new_page()

[David Hildenbrand]

On 26.10.20 18:33, Vlastimil Babka wrote:
> prep_new_page() will always zero a new page (regardless of __GFP_ZERO) when
> init_on_alloc is enabled, but will also always skip zeroing if the page was
> already zeroed on free by init_on_free or page poisoning.
>
> The latter check implemented by free_pages_prezeroed() can involve two
> different static keys. As prep_new_page() is really a hot path, let's introduce
> a single static key free_pages_not_prezeroed for this purpose and initialize it
> in init_mem_debugging().

Is this actually observable in practice? This smells like 
micro-optimization to me.

Also, I thought the whole reason for static keys is to have basically no 
overhead at runtime, so I wonder if replacing two static key checks by a 
single one actually makes *some* difference.

--
Thanks,

David / dhildenb