Re: [GIT PULL] slab for 5.19

[Linus Torvalds]

On Mon, May 23, 2022 at 2:54 AM Vlastimil Babka <vbabka@xxxxxxx> wrote:
>
>   The stackdepot conversion was already attempted last year but
>   reverted by ae14c63a9f20. The memory overhead (while not actually
>   enabled on boot) has been meanwhile solved by making the large
>   stackdepot allocation dynamic.

Why do I still see

  +config STACK_HASH_ORDER
  +       int "stack depot hash size (12 => 4KB, 20 => 1024KB)"
  +       range 12 20
  +       default 20

there then?

All that seems to have happened is that it's not a static allocation
any more, but it's still a big allocation very early at boot by
default.

The people who complained about this last time were on m68k machines
iirc, and 1MB there is not insignificant.

It's not at all clear to me why that allocation should be that kind of
fixed number, and if it's a fixed number, why it should be the maximum
one by default. That seems entirely broken.

I've pulled this, but considering that it got reverted once, I'm
really fed up with this kind of thing.  This needs to be fixed.

Because I'm _this_ close to just reverting it again, and saying "No,
you tried this crap already, didn't learn from the last time, and then
did the same thing all over again just in a different guise".

                    Linus