Re: [PATCH 2/2] mm: drop PF_MEMALLOC_NORECLAIM

Michal Hocko
2024-08-26T16:54:05Z

On Mon 26-08-24 21:48:34, Yafang Shao wrote:
> On Mon, Aug 26, 2024 at 4:53 PM Michal Hocko <mhocko@kernel.org> wrote:
> >
> > From: Michal Hocko <mhocko@suse.com>
> >
> > There is no existing user of the flag and the flag is dangerous because
> > a nested allocation context can use GFP_NOFAIL which could cause
> > unexpected failure. Such a code would be hard to maintain because it
> > could be deeper in the call chain.
> >
> > PF_MEMALLOC_NORECLAIM has been added even when it was pointed out [1]
> > that such a allocation contex is inherently unsafe if the context
> > doesn't fully control all allocations called from this context.
> >
> > [1] https://lore.kernel.org/all/ZcM0xtlKbAOFjv5n@tiehlicka/
> >
> > Signed-off-by: Michal Hocko <mhocko@suse.com>
> > ---
> > include/linux/sched.h | 1 -
> > include/linux/sched/mm.h | 7 ++-----
> > 2 files changed, 2 insertions(+), 6 deletions(-)
> >
> > diff --git a/include/linux/sched.h b/include/linux/sched.h
> > index f8d150343d42..72dad3a6317a 100644
> > --- a/include/linux/sched.h
> > +++ b/include/linux/sched.h
> > @@ -1657,7 +1657,6 @@ extern struct pid *cad_pid;
> > * I am cleaning dirty pages from some other bdi. */
> > #define PF_KTHREAD 0x00200000 /* I am a kernel thread */
> > #define PF_RANDOMIZE 0x00400000 /* Randomize virtual address space */
> > -#define PF_MEMALLOC_NORECLAIM 0x00800000 /* All allocation requests will clear __GFP_DIRECT_RECLAIM */
>
> To maintain consistency with the other unused bits, it would be better
> to define PF__HOLE__00800000 instead.

OK

--
Michal Hocko
SUSE Labs