Re: [PATCH] mm: fix sleeping function warning in alloc_swap_info

[Linus Torvalds <torvalds@linux-foundation.org>]

On Tue, Jan 29, 2019 at 6:54 PM Tetsuo Handa
<penguin-kernel@i-love.sakura.ne.jp> wrote:
>
> Then, do we automatically defer vfree() to mm_percpu_wq context?

We might do that, and say "if you call vfree with interrupts disabled,
it gets deferred".

That said, the deferred case should generally not be a common case
either. It has real issues, one of which is simply that particularly
on 32-bit architectures we can run out of vmalloc space even normally,
and if there are loads that do a lot of allocation and then deferred
frees, that problem could become really bad.

So I'd almost be happier having a warning if we end up doing the TLB
flush and defer. At least to find *what* people do.

And I do wonder if we should just always warn, and have that
"might_sleep()", and simply say "if you do vfree from interrupts or
with interrupts disabled, you really should be aware of these kinds of
issues, and you really should *show* that you are aware by using
vfree_atomic()".

                     Linus