Commit 9a8da05d authored by Michal Hocko's avatar Michal Hocko Committed by Andrew Morton
Browse files

Revert "mm: introduce PF_MEMALLOC_NORECLAIM, PF_MEMALLOC_NOWARN" 

This reverts commit eab0af90.

There is no existing user of those flags.  PF_MEMALLOC_NOWARN 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.

While PF_MEMALLOC_NOWARN is not dangerous the way PF_MEMALLOC_NORECLAIM is
it doesn't have any user and as Matthew has pointed out we are running out
of those flags so better reclaim it without any real users.

[1] https://lore.kernel.org/all/ZcM0xtlKbAOFjv5n@tiehlicka/

Link: https://lkml.kernel.org/r/20240926172940.167084-3-mhocko@kernel.org


Signed-off-by: default avatarMichal Hocko <mhocko@suse.com>
Reviewed-by: default avatarMatthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Reviewed-by: default avatarDave Chinner <dchinner@redhat.com>
Reviewed-by: default avatarVlastimil Babka <vbabka@suse.cz>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <brauner@kernel.org>
Cc: James Morris <jmorris@namei.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Cc: Paul Moore <paul@paul-moore.com>
Cc: Serge E. Hallyn <serge@hallyn.com>
Cc: Yafang Shao <laoar.shao@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 9897713f

include/linux/sched.h

+2 −2
Original line number Diff line number Diff line
@@ -1681,8 +1681,8 @@ 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 */

#define PF_MEMALLOC_NOWARN	0x01000000	/* All allocation requests will inherit __GFP_NOWARN */

#define PF__HOLE__00800000	0x00800000

#define PF__HOLE__01000000	0x01000000

#define PF__HOLE__02000000	0x02000000

#define PF_NO_SETAFFINITY	0x04000000	/* Userland is not allowed to meddle with cpus_mask */

#define PF_MCE_EARLY		0x08000000      /* Early kill for mce process policy */

include/linux/sched/mm.h

+4 −13
Original line number Diff line number Diff line
@@ -251,25 +251,16 @@ static inline gfp_t current_gfp_context(gfp_t flags) 
{

	unsigned int pflags = READ_ONCE(current->flags);



	if (unlikely(pflags & (PF_MEMALLOC_NOIO |

			       PF_MEMALLOC_NOFS |

			       PF_MEMALLOC_NORECLAIM |

			       PF_MEMALLOC_NOWARN |

			       PF_MEMALLOC_PIN))) {

	if (unlikely(pflags & (PF_MEMALLOC_NOIO | PF_MEMALLOC_NOFS | PF_MEMALLOC_PIN))) {

		/*

		 * Stronger flags before weaker flags:

		 * NORECLAIM implies NOIO, which in turn implies NOFS

		 * NOIO implies both NOIO and NOFS and it is a weaker context

		 * so always make sure it makes precedence

		 */

		if (pflags & PF_MEMALLOC_NORECLAIM)

			flags &= ~__GFP_DIRECT_RECLAIM;

		else if (pflags & PF_MEMALLOC_NOIO)

		if (pflags & PF_MEMALLOC_NOIO)

			flags &= ~(__GFP_IO | __GFP_FS);

		else if (pflags & PF_MEMALLOC_NOFS)

			flags &= ~__GFP_FS;



		if (pflags & PF_MEMALLOC_NOWARN)

			flags |= __GFP_NOWARN;



		if (pflags & PF_MEMALLOC_PIN)

			flags &= ~__GFP_MOVABLE;

	}