[PATCH 2/2] Revert "mm: introduce PF_MEMALLOC_NORECLAIM, PF_MEMALLOC_NOWARN"

Michal Hocko
2024-09-02T09:52:15Z

From: Michal Hocko <mhocko@suse.com>

This reverts commit eab0af905bfc3e9c05da2ca163d76a1513159aa4.

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/

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>
Signed-off-by: Michal Hocko <mhocko@suse.com>
---
include/linux/sched.h | 4 ++--
include/linux/sched/mm.h | 17 ++++-------------
2 files changed, 6 insertions(+), 15 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index f8d150343d42..731ff1078c9e 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1657,8 +1657,8 @@ 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 */
diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
index 91546493c43d..07c4fde32827 100644
--- a/include/linux/sched/mm.h
+++ b/include/linux/sched/mm.h
@@ -258,25 +258,16 @@ 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;
}
--
2.46.0