Re: [PATCH] mm/slob: Remove unnecessary page_mapcount_reset() function call

Re: [PATCH] mm/slob: Remove unnecessary page_mapcount_reset() function call

[Vlastimil Babka]

On 12/12/21 07:52, Hyeonggon Yoo wrote:
> After commit f1ac9059ca34 ("mm/sl*b: Differentiate struct slab fields
> by sl*b implementations"), we can reorder fields of struct slab
> depending on slab allocator.
> 
> For now, page_mapcount_reset() is called because page->_mapcount and
> slab->units have same offset. But this is not necessary for
> struct slab. Use unused field for units instead.
> 
> Signed-off-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>

Will add to the series, thanks!

> ---
>  mm/slab.h | 4 ++--
>  mm/slob.c | 1 -
>  2 files changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/slab.h b/mm/slab.h
> index 90d7fceba470..dd0480149d38 100644
> --- a/mm/slab.h
> +++ b/mm/slab.h
> @@ -50,8 +50,8 @@ struct slab {
>  	struct list_head slab_list;
>  	void * __unused_1;
>  	void *freelist;		/* first free block */
> -	void * __unused_2;
> -	int units;
> +	long units;
> +	unsigned int __unused_2;
>  
>  #else
>  #error "Unexpected slab allocator configured"
> diff --git a/mm/slob.c b/mm/slob.c
> index 39b651b3e6e7..7b2d2c7d69cc 100644
> --- a/mm/slob.c
> +++ b/mm/slob.c
> @@ -404,7 +404,6 @@ static void slob_free(void *block, int size)
>  			clear_slob_page_free(sp);
>  		spin_unlock_irqrestore(&slob_lock, flags);
>  		__ClearPageSlab(slab_page(sp));
> -		page_mapcount_reset(slab_page(sp));
>  		slob_free_pages(b, 0);
>  		return;
>  	}