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

Yafang Shao
2024-08-26T13:49:11Z

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.

--
Regards

Yafang