mm: introduce memalloc_flags_{save,restore}

Our proliferation of memalloc_*_{save,restore} APIs is getting a bit
silly, this adds a generic version and converts the existing
save/restore functions to wrappers.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Darrick J. Wong <djwong@kernel.org>
Cc: linux-mm@kvack.org
Acked-by: Vlastimil Babka <vbabka@suse.cz>

include/linux/sched/mm.h

@@ -306,6 +306,24 @@ static inline void might_alloc(gfp_t gfp_mask)
 	might_sleep_if(gfpflags_allow_blocking(gfp_mask));
 }
 
+/**
+ * memalloc_flags_save - Add a PF_* flag to current->flags, save old value
+ *
+ * This allows PF_* flags to be conveniently added, irrespective of current
+ * value, and then the old version restored with memalloc_flags_restore().
+ */
+static inline unsigned memalloc_flags_save(unsigned flags)
+{
+	unsigned oldflags = ~current->flags & flags;
+	current->flags |= flags;
+	return oldflags;
+}
+
+static inline void memalloc_flags_restore(unsigned flags)
+{
+	current->flags &= ~flags;
+}
+
 /**
  * memalloc_noio_save - Marks implicit GFP_NOIO allocation scope.
  *
@@ -319,9 +337,7 @@ static inline void might_alloc(gfp_t gfp_mask)
  */
 static inline unsigned int memalloc_noio_save(void)
 {
-	unsigned int flags = current->flags & PF_MEMALLOC_NOIO;
-	current->flags |= PF_MEMALLOC_NOIO;
-	return flags;
+	return memalloc_flags_save(PF_MEMALLOC_NOIO);
 }
 
 /**
@@ -334,7 +350,7 @@ static inline unsigned int memalloc_noio_save(void)
  */
 static inline void memalloc_noio_restore(unsigned int flags)
 {
-	current->flags = (current->flags & ~PF_MEMALLOC_NOIO) | flags;
+	memalloc_flags_restore(flags);
 }
 
 /**
@@ -350,9 +366,7 @@ static inline void memalloc_noio_restore(unsigned int flags)
  */
 static inline unsigned int memalloc_nofs_save(void)
 {
-	unsigned int flags = current->flags & PF_MEMALLOC_NOFS;
-	current->flags |= PF_MEMALLOC_NOFS;
-	return flags;
+	return memalloc_flags_save(PF_MEMALLOC_NOFS);
 }
 
 /**
@@ -365,32 +379,27 @@ static inline unsigned int memalloc_nofs_save(void)
  */
 static inline void memalloc_nofs_restore(unsigned int flags)
 {
-	current->flags = (current->flags & ~PF_MEMALLOC_NOFS) | flags;
+	memalloc_flags_restore(flags);
 }
 
 static inline unsigned int memalloc_noreclaim_save(void)
 {
-	unsigned int flags = current->flags & PF_MEMALLOC;
-	current->flags |= PF_MEMALLOC;
-	return flags;
+	return memalloc_flags_save(PF_MEMALLOC);
 }
 
 static inline void memalloc_noreclaim_restore(unsigned int flags)
 {
-	current->flags = (current->flags & ~PF_MEMALLOC) | flags;
+	memalloc_flags_restore(flags);
 }
 
 static inline unsigned int memalloc_pin_save(void)
 {
-	unsigned int flags = current->flags & PF_MEMALLOC_PIN;
-
-	current->flags |= PF_MEMALLOC_PIN;
-	return flags;
+	return memalloc_flags_save(PF_MEMALLOC_PIN);
 }
 
 static inline void memalloc_pin_restore(unsigned int flags)
 {
-	current->flags = (current->flags & ~PF_MEMALLOC_PIN) | flags;
+	memalloc_flags_restore(flags);
 }
 
 #ifdef CONFIG_MEMCG