Re: [PATCH v3 04/19] mm: slub: implement SLUB version of obj_to_index()

[Roman Gushchin]

On Fri, May 15, 2020 at 09:45:30PM +0000, Christoph Lameter wrote:
> On Tue, 12 May 2020, Roman Gushchin wrote:
> 
> > > Add it to the metadata at the end of the object. Like the debugging
> > > information or the pointer for RCU freeing.
> >
> > Enabling debugging metadata currently disables the cache merging.
> > I doubt that it's acceptable to sacrifice the cache merging in order
> > to embed the memcg pointer?
> 
> Well then keep the merging even if you have a memcg pointer.
> 
> The disabling for debugging is only to simplify debugging. You dont have
> to deal with multiple caches actually using the same storage structures.
> 
> > Figuring out all these details will likely take several weeks, so the whole
> > thing will be delayed for one-two major releases (in the best case). Given that
> > the current implementation saves ~40% of slab memory, I think there is some value
> > in delivering it as it is. So I wonder if the idea of embedding the pointer
> > should be considered a blocker, or it can be implemented of top of the proposed
> > code (given it's not a user-facing api or something like this)?
> 
> Sorry no idea from my end here.

Ok, then I'll continue working on the embedding the pointer as an enhancement
*on top* of the current patchset. As I showed in my other e-mail, switching
to a different way of obj_cgroup storage is fairly trivial and doesn't change
much in the rest of the patchset.

Please, let me know if you're not ok with it.

Thanks!