On Thu, 2013-01-17 at 21:28 +0000, Christoph Lameter wrote:
> On Thu, 17 Jan 2013, Steven Rostedt wrote:
>
> > > --- a/mm/slub.c
> > > +++ b/mm/slub.c
> > > @@ -2399,7 +2399,7 @@ redo:
> > >
> > > object = c->freelist;
> > > page = c->page;
We should add a BUG_ON(!page) if it's a problem. I wasted a bit of time
finding this bug just because it triggered in a static inline function,
and I didn't have the vmlinuz file to play with. I had to ask someone
else to do the work for me.
> > > - if (unlikely(!object || !node_match(page, node)))
> > > + if (unlikely(!object || !page || !node_match(page, node)))
> >
> > I'm still trying to see if c->freelist != NULL and c->page == NULL isn't
> > a bug. The cmpxchg_doubles are a little confusing. If it's not expected
> > that page is NULL but freelist isn't than we need to figure out why it
> > happened.
>
> hmmm.. We may want to change the sequence of updates to c->page and
> c->freelist. Update c->freelist to be NULL first so that we always enter
> the slow path for these cases where we can do more expensive
> synchronization.
>
> Index: linux/mm/slub.c
> ===================================================================
> --- linux.orig/mm/slub.c 2013-01-15 10:42:08.490183607 -0600
> +++ linux/mm/slub.c 2013-01-17 15:27:48.973051155 -0600
> @@ -1993,8 +1993,8 @@ static inline void flush_slab(struct kme
> deactivate_slab(s, c->page, c->freelist);
>
> c->tid = next_tid(c->tid);
> - c->page = NULL;
> c->freelist = NULL;
> + c->page = NULL;
I'm assuming that this is to deal with the same CPU being able to touch
the code?
If so, it requires "barrier()". If this can affect other CPUs, then we
need a smp_wmb() here, and smp_rmb() where it matters.
-- Steve
> }
>
> /*
> @@ -2227,8 +2227,8 @@ redo:
> if (unlikely(!node_match(page, node))) {
> stat(s, ALLOC_NODE_MISMATCH);
> deactivate_slab(s, page, c->freelist);
> - c->page = NULL;
> c->freelist = NULL;
> + c->page = NULL;
> goto new_slab;
> }
>
> @@ -2239,8 +2239,8 @@ redo:
> */
> if (unlikely(!pfmemalloc_match(page, gfpflags))) {
> deactivate_slab(s, page, c->freelist);
> - c->page = NULL;
> c->freelist = NULL;
> + c->page = NULL;
> goto new_slab;
> }
>
--
To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
