Re: [RFC-PATCH 1/2] mm: Add __GFP_NO_LOCKS flag

Michal Hocko
2020-08-11T10:21:35Z

On Tue 11-08-20 11:18:07, Uladzislau Rezki wrote:
> On Mon, Aug 10, 2020 at 09:25:25PM +0200, Michal Hocko wrote:
> > On Mon 10-08-20 18:07:39, Uladzislau Rezki wrote:
> > > > On Sun 09-08-20 22:43:53, Uladzislau Rezki (Sony) wrote:
[...]
> > > As i described before, calling the __get_free_page(0) with 0 as argument
> > > will solve the (a). How correctly is it? From my point of view the logic
> > > that bypass the wakeup path should be explicitly defined.
> >
> > gfp_mask == 0 is GFP_NOWAIT (aka an atomic allocation request) which
> > doesn't wake up kswapd. So if the wakeup is a problem then this would be
> > a way to go.
> >
> What do you mean Michal? gfp_mask 0 != GFP_NOWAIT:
>
> #define GFP_NOWAIT (__GFP_KSWAPD_RECLAIM)
>
> it does wakeup of the kswapd. Or am i missing something? Please comment.
> If we are about to avoid the kswapd, should we define something special?
>
> #define GFP_NOWWAKE_KSWAPD 0

Sorry, I was more cryptic than necessary. What I meant is that
GFP_NOWAIT is the basic non-sleepable allocation. It does wake up
kswapd but a lack of it can be expressed GFP_NOWAIT & ~__GFP_KSWAPD_RECLAIM
which is 0, now. The mouthfull variant is better for future
maintainability.
--
Michal Hocko
SUSE Labs