Re: [PATCH v2 3/4] gfp: mm: introduce __GFP_NO_AUTOINIT

[Michal Hocko <mhocko@kernel.org>]

[It would be great to keep people involved in the previous version in the
CC list]

On Tue 14-05-19 16:35:36, Alexander Potapenko wrote:
> When passed to an allocator (either pagealloc or SL[AOU]B),
> __GFP_NO_AUTOINIT tells it to not initialize the requested memory if the
> init_on_alloc boot option is enabled. This can be useful in the cases
> newly allocated memory is going to be initialized by the caller right
> away.
> 
> __GFP_NO_AUTOINIT doesn't affect init_on_free behavior, except for SLOB,
> where init_on_free implies init_on_alloc.
> 
> __GFP_NO_AUTOINIT basically defeats the hardening against information
> leaks provided by init_on_alloc, so one should use it with caution.
> 
> This patch also adds __GFP_NO_AUTOINIT to alloc_pages() calls in SL[AOU]B.
> Doing so is safe, because the heap allocators initialize the pages they
> receive before passing memory to the callers.

I still do not like the idea of a new gfp flag as explained in the
previous email. People will simply use it incorectly or arbitrarily.
We have that juicy experience from the past.

Freeing a memory is an opt-in feature and the slab allocator can already
tell many (with constructor or GFP_ZERO) do not need it.

So can we go without this gfp thing and see whether somebody actually
finds a performance problem with the feature enabled and think about
what can we do about it rather than add this maint. nightmare from the
very beginning?
-- 
Michal Hocko
SUSE Labs