Re: [RFC PATCH 00/30] Code tagging framework and applications

[Kent Overstreet <kent.overstreet@xxxxxxxxx>]

On Wed, Sep 07, 2022 at 11:49:37PM -0700, Suren Baghdasaryan wrote:
> I would really appreciate if everyone could please stick to the
> technical side of the conversation. That way we can get some
> constructive feedback. Everything else is not helpful and at best is a
> distraction.
> Maintenance burden is a price we pay and I think it's the prerogative
> of the maintainers to take that into account. Our job is to prove that
> the price is worth paying.

Well said.

I'd also like to add - slab.h does look pretty overgrown and messy. We've grown
a _lot_ of special purpose memory allocation interfaces, and I think it probably
is time to try and wrangle that back.

The API complexity isn't just an issue for this patch - it's an issue for
anything that has to wrap and plumb through memory allocation interfaces. It's a
pain point for the Rust people, and also comes in e.g. the mempool API.

I think we should keep going with the memalloc_no*_save()/restore() approach,
and extend it to other things:

 - memalloc_nowait_save()
 - memalloc_highpri_save()

(these two get you GFP_ATOMIC).

Also, I don't think these all need to be separate functions, we could have

memalloc_gfp_apply()
memalloc_gfp_restore()

which simply takes a gfp flags argument and applies it to the current
PF_MEMALLOC flags.

We've had long standing bugs where vmalloc() can't correctly take gfp flags
because some of the allocations it does for page tables don't have it correctly
plumbed through; switching to the memalloc_*_(save|restore) is something people
have been wanting in order to fix this - for years. Actually following through
and completing this would let us kill the gfp flags arguments to our various
memory allocators entirely.

I think we can do the same thing with the numa node parameter - kill
kmalloc_node() et. all, move it to task_struct with a set of save/restore
functions.

There's probably other things we can do to simplify slab.h if we look more. I've
been hoping to start pushing patches for some of this stuff - it's going to be
some time before I can get to it though, can only handle so many projects in
flight at a time :)