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Revert "mm: introduce PF_MEMALLOC_NORECLAIM, PF_MEMALLOC_NOWARN"

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This reverts commit eab0af905b.

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: Michal Hocko <mhocko@suse.com>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Vlastimil 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: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Michal Hocko 2024-09-26 19:11:51 +02:00 committed by Andrew Morton
parent 9897713fe1
commit 9a8da05d7a
2 changed files with 6 additions and 15 deletions
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4
include/linux/sched.h
View File

@ -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 */

17
include/linux/sched/mm.h
View File

@ -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;
}