Re: [PATCH v3 2/6] mm/slab: Plumb kmem_buckets into __do_kmalloc_node()

Kent Overstreet
2024-05-31T16:51:41Z

On Fri, May 31, 2024 at 09:48:49AM -0700, Kees Cook wrote:
> On Fri, May 24, 2024 at 11:01:40AM -0400, Kent Overstreet wrote:
> > On Wed, Apr 24, 2024 at 02:40:59PM -0700, Kees Cook wrote:
> > > To be able to choose which buckets to allocate from, make the buckets
> > > available to the lower level kmalloc interfaces by adding them as the
> > > first argument. Where the bucket is not available, pass NULL, which means
> > > "use the default system kmalloc bucket set" (the prior existing behavior),
> > > as implemented in kmalloc_slab().
> >
> > I thought the plan was to use codetags for this? That would obviate the
> > need for all this plumbing.
> >
> > Add fields to the alloc tag for:
> > - allocation size (or 0 if it's not a compile time constant)
> > - union of kmem_cache, kmem_buckets, depending on whether the
> > allocation size is constant or not
>
> I want to provide "simple" (low-hanging fruit) coverage that can live
> separately from the codetags-based coverage. The memory overhead for
> this patch series is negligible, but I suspect the codetags expansion,
> while not giant, will be more than some deployments will want. I want
> to avoid an all-or-nothing solution -- which is why I had intended this
> to be available "by default".

technically there's no reason for your thing to depend on
CONFIG_CODETAGGING at all, that's the infrastructure for finding
codetags for e.g. /proc/allocinfo. you'd just be using the alloc_hoos()
macro and struct alloc_tag as a place to stash the kmem_buckets pointer.