[PATCH 1/2] mm: Add memalloc_nowait_{save,restore}

[Yafang Shao <laoar.shao@gmail.com>]

The PF_MEMALLOC_NORECLAIM flag was introduced in commit eab0af905bfc
("mm: introduce PF_MEMALLOC_NORECLAIM, PF_MEMALLOC_NOWARN"). To complement
this, let's add two helper functions, memalloc_nowait_{save,restore}, which
will be useful in scenarios where we want to avoid waiting for memory
reclamation.

Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
---
 include/linux/sched/mm.h | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
index 91546493c43d..4fbae0013166 100644
--- a/include/linux/sched/mm.h
+++ b/include/linux/sched/mm.h
@@ -484,6 +484,36 @@ static inline void memalloc_pin_restore(unsigned int flags)
 	memalloc_flags_restore(flags);
 }
 
+/**
+ * memalloc_nowait_save - Marks implicit ~__GFP_DIRECT_RECLAIM allocation scope.
+ *
+ * This functions marks the beginning of the ~__GFP_DIRECT_RECLAIM allocation
+ * scope. All further allocations will implicitly drop __GFP_DIRECT_RECLAIM flag
+ * and so they are won't wait for direct memory reclaiming. Use
+ * memalloc_nowait_restore to end the scope with flags returned by this
+ * function.
+ *
+ * Context: This function is safe to be used from any context.
+ * Return: The saved flags to be passed to memalloc_nowait_restore.
+ */
+static inline unsigned int memalloc_nowait_save(void)
+{
+	return memalloc_flags_save(PF_MEMALLOC_NORECLAIM);
+}
+
+/**
+ * memalloc_nofs_restore - Ends the implicit ~__GFP_DIRECT_RECLAIM scope.
+ * @flags: Flags to restore.
+ *
+ * Ends the implicit ~__GFP_DIRECT_RECLAIM scope started by memalloc_nowait_save
+ * function. Always make sure that the given flags is the return value from the
+ * pairing memalloc_nowait_save call.
+ */
+static inline void memalloc_nowait_restore(unsigned int flags)
+{
+	memalloc_flags_restore(flags);
+}
+
 #ifdef CONFIG_MEMCG
 DECLARE_PER_CPU(struct mem_cgroup *, int_active_memcg);
 /**
-- 
2.43.5