Re: [PATCH 4/4] don't do __ClearPageSlab before freeing slab page.

[David Rientjes <rientjes@google.com>]

On Thu, 21 Jun 2012, Glauber Costa wrote:

> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 6092f33..fdec73e 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -698,8 +698,10 @@ static bool free_pages_prepare(struct page *page, unsigned int order)
>  
>  	if (PageAnon(page))
>  		page->mapping = NULL;
> -	for (i = 0; i < (1 << order); i++)
> +	for (i = 0; i < (1 << order); i++) {
> +		__ClearPageSlab(page + i);
>  		bad += free_pages_check(page + i);
> +	}
>  	if (bad)
>  		return false;
>  
> @@ -2561,6 +2563,7 @@ EXPORT_SYMBOL(get_zeroed_page);
>  void __free_pages(struct page *page, unsigned int order)
>  {
>  	if (put_page_testzero(page)) {
> +		__ClearPageSlab(page);
>  		if (order == 0)
>  			free_hot_cold_page(page, 0);
>  		else

These are called from a number of different places that has nothing to do 
with slab so it's certainly out of place here.  Is there really no 
alternative way of doing this?

> diff --git a/mm/slab.c b/mm/slab.c
> index cb6da05..3e578fc 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -1821,11 +1821,6 @@ static void kmem_freepages(struct kmem_cache *cachep, void *addr)
>  	else
>  		sub_zone_page_state(page_zone(page),
>  				NR_SLAB_UNRECLAIMABLE, nr_freed);
> -	while (i--) {
> -		BUG_ON(!PageSlab(page));
> -		__ClearPageSlab(page);
> -		page++;
> -	}
>  	if (current->reclaim_state)
>  		current->reclaim_state->reclaimed_slab += nr_freed;
>  	free_pages((unsigned long)addr, cachep->gfporder);

And we lose this validation in slab.

I'm hoping there's an alternative.

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