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

Neil Brown
2008-08-12T05:35:14Z

On Thursday July 24, a.p.zijlstra@chello.nl 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