mm: introduce PF_MEMALLOC_NORECLAIM, PF_MEMALLOC_NOWARN

Introduce PF_MEMALLOC_* equivalents of some GFP_ flags:

PF_MEMALLOC_NORECLAIM -> GFP_NOWAIT
PF_MEMALLOC_NOWARN -> __GFP_NOWARN

Cc: Vlastimil Babka <[e-mail]>
Cc: Matthew Wilcox <[e-mail]>
Cc: Michal Hocko <[e-mail]>
Cc: Darrick J. Wong <[e-mail]>
Cc: [e-mail]
Signed-off-by: Kent Overstreet <[e-mail]>

include/linux/sched.h

···
 						 * 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__HOLE__00800000	0x00800000
-#define PF__HOLE__01000000	0x01000000
+#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__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

···
 {
 	unsigned int pflags = READ_ONCE(current->flags);
 
-	if (unlikely(pflags & (PF_MEMALLOC_NOIO | PF_MEMALLOC_NOFS | PF_MEMALLOC_PIN))) {
+	if (unlikely(pflags & (PF_MEMALLOC_NOIO |
+			       PF_MEMALLOC_NOFS |
+			       PF_MEMALLOC_NORECLAIM |
+			       PF_MEMALLOC_NOWARN |
+			       PF_MEMALLOC_PIN))) {
 		/*
-		 * NOIO implies both NOIO and NOFS and it is a weaker context
-		 * so always make sure it makes precedence
+		 * Stronger flags before weaker flags:
+		 * NORECLAIM implies NOIO, which in turn implies NOFS
 		 */
-		if (pflags & PF_MEMALLOC_NOIO)
+		if (pflags & PF_MEMALLOC_NORECLAIM)
+			flags &= ~__GFP_DIRECT_RECLAIM;
+		else 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;