Re: [PATCH 05/30] mm: slb: add knowledge of reserve pages

[Neil Brown]

On Thursday July 24, a.p.zijlstra@xxxxxxxxx wrote:
> Restrict objects from reserve slabs (ALLOC_NO_WATERMARKS) to allocation
> contexts that are entitled to it. This is done to ensure reserve pages don't
> leak out and get consumed.

This looks good (we are still missing slob though, aren't we :-( )

> @@ -1526,7 +1540,7 @@ load_freelist:
>  	object = c->page->freelist;
>  	if (unlikely(!object))
>  		goto another_slab;
> -	if (unlikely(SLABDEBUG && PageSlubDebug(c->page)))
> +	if (unlikely(PageSlubDebug(c->page) || c->reserve))
>  		goto debug;

This looks suspiciously like debugging code that you have left in.
Is it??

> @@ -265,7 +267,8 @@ struct array_cache {
>  	unsigned int avail;
>  	unsigned int limit;
>  	unsigned int batchcount;
> -	unsigned int touched;
> +	unsigned int touched:1,
> +		     reserve:1;

This sort of thing always worries me.
It is a per-cpu data structure so you won't get SMP races corrupting
fields.  But you do get read-modify-write in place of simple updates.
I guess it's not a problem..  But it worries me :-)


NeilBrown
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