Messages in this thread | | | Date | Wed, 11 Apr 2018 16:56:52 -0700 | From | Matthew Wilcox <> | Subject | Re: [PATCH v2 2/2] slab: __GFP_ZERO is incompatible with a constructor |
| |
On Wed, Apr 11, 2018 at 04:11:17PM -0500, Christopher Lameter wrote: > On Wed, 11 Apr 2018, Matthew Wilcox wrote: > > > Please put this in a code path that is enabled by specifying > > > > > > slub_debug > > > > > > on the kernel command line. > > > > I don't understand. First, I had: > > > > if (unlikely(gfpflags & __GFP_ZERO) && object && !WARN_ON_ONCE(s->ctor)) > > > > and you didn't like that because it was putting checking into a (semi)fast > > path. Now you want me to add a check for slub_debug somewhere? I dont > > see an existing one I can leverage that will hit on every allocation. > > Perhaps I'm missing something. > > The WARN_ON is only enabled when you configure and build the kernel with > debugging enabled (CONFIG_VM_DEBUG). That is a compile time debugging > feature like supported by SLAB.
Yes. I want to have an option to check *every single* allocation.
> "slub_debug" enables kmem_cache->flags & SLAB_DEBUG and that forces all > fastpath processing to be disabled. Thus you can check reliably in the > slow path only for the GFP_ZERO problem. > > Add the check to the other debug stuff already there. F.e. in > alloc_debug_processing() or after > > if (kmem_cache_debug(s) ... > > in ____slab_alloc()
I don't see how that works ... can you explain a little more?
I see ___slab_alloc() is called from __slab_alloc(). And I see slab_alloc_node does this:
object = c->freelist; page = c->page; if (unlikely(!object || !node_match(page, node))) { object = __slab_alloc(s, gfpflags, node, addr, c); stat(s, ALLOC_SLOWPATH);
But I don't see how slub_debug leads to c->freelist always being NULL. It looks like it gets repopulated from page->freelist in ___slab_alloc() at the load_freelist label.
| |