The patch titled
Subject: Revert "mm: introduce PF_MEMALLOC_NORECLAIM, PF_MEMALLOC_NOWARN"
has been added to the -mm mm-unstable branch. Its filename is
revert-mm-introduce-pf_memalloc_noreclaim-pf_memalloc_nowarn.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/revert-mm-introduce-pf_memalloc_noreclaim-pf_memalloc_nowarn.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Michal Hocko <mhocko@xxxxxxxx>
Subject: Revert "mm: introduce PF_MEMALLOC_NORECLAIM, PF_MEMALLOC_NOWARN"
Date: Mon, 2 Sep 2024 11:51:50 +0200
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/
Link: https://lkml.kernel.org/r/20240902095203.1559361-3-mhocko@xxxxxxxxxx
Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
Reviewed-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Reviewed-by: Dave Chinner <dchinner@xxxxxxxxxx>
Reviewed-by: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Christian Brauner <brauner@xxxxxxxxxx>
Cc: James Morris <jmorris@xxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Kent Overstreet <kent.overstreet@xxxxxxxxx>
Cc: Paul Moore <paul@xxxxxxxxxxxxxx>
Cc: Serge E. Hallyn <serge@xxxxxxxxxx>
Cc: "Theodore Ts'o" <tytso@xxxxxxx>
Cc: Yafang Shao <laoar.shao@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/sched.h | 4 ++--
include/linux/sched/mm.h | 17 ++++-------------
2 files changed, 6 insertions(+), 15 deletions(-)
--- a/include/linux/sched.h~revert-mm-introduce-pf_memalloc_noreclaim-pf_memalloc_nowarn
+++ a/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 */
--- a/include/linux/sched/mm.h~revert-mm-introduce-pf_memalloc_noreclaim-pf_memalloc_nowarn
+++ a/include/linux/sched/mm.h
@@ -251,25 +251,16 @@ static inline gfp_t current_gfp_context(
{
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;
}
_
Patches currently in -mm which might be from mhocko@xxxxxxxx are
bcachefs-do-not-use-pf_memalloc_noreclaim.patch
bcachefs-do-not-use-pf_memalloc_noreclaim-fix.patch
revert-mm-introduce-pf_memalloc_noreclaim-pf_memalloc_nowarn.patch
