3 files changed, 34 insertions, 8 deletions

diff --git a/include/linux/gfp.h b/include/linux/gfp.h
index 978232a3b4ae..2bfcfd33e476 100644
--- a/include/linux/gfp.h
+++ b/include/linux/gfp.h
@@ -210,8 +210,16 @@ struct vm_area_struct;
  *
  * GFP_NOIO will use direct reclaim to discard clean pages or slab pages
  *   that do not require the starting of any physical IO.
+ *   Please try to avoid using this flag directly and instead use
+ *   memalloc_noio_{save,restore} to mark the whole scope which cannot
+ *   perform any IO with a short explanation why. All allocation requests
+ *   will inherit GFP_NOIO implicitly.
  *
  * GFP_NOFS will use direct reclaim but will not use any filesystem interfaces.
+ *   Please try to avoid using this flag directly and instead use
+ *   memalloc_nofs_{save,restore} to mark the whole scope which cannot/shouldn't
+ *   recurse into the FS layer with a short explanation why. All allocation
+ *   requests will inherit GFP_NOFS implicitly.
  *
  * GFP_USER is for userspace allocations that also need to be directly
  *   accessibly by the kernel or hardware. It is typically used by hardware
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 8ac11465ac5b..993e7e25a3a5 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1224,9 +1224,9 @@ extern struct pid *cad_pid;
 #define PF_USED_ASYNC           0x00004000      /* Used async_schedule*(), used by module init */
 #define PF_NOFREEZE             0x00008000      /* This thread should not be frozen */
 #define PF_FROZEN               0x00010000      /* Frozen for system suspend */
-#define PF_FSTRANS              0x00020000      /* Inside a filesystem transaction */
-#define PF_KSWAPD               0x00040000      /* I am kswapd */
-#define PF_MEMALLOC_NOIO        0x00080000      /* Allocating memory without IO involved */
+#define PF_KSWAPD               0x00020000      /* I am kswapd */
+#define PF_MEMALLOC_NOFS        0x00040000      /* All allocation requests will inherit GFP_NOFS */
+#define PF_MEMALLOC_NOIO        0x00080000      /* All allocation requests will inherit GFP_NOIO */
 #define PF_LESS_THROTTLE        0x00100000      /* Throttle me less: I clean memory */
 #define PF_KTHREAD              0x00200000      /* I am a kernel thread */
 #define PF_RANDOMIZE            0x00400000      /* Randomize virtual address space */
@@ -1237,8 +1237,6 @@ extern struct pid *cad_pid;
 #define PF_FREEZER_SKIP         0x40000000      /* Freezer should not count it as freezable */
 #define PF_SUSPEND_TASK         0x80000000      /* This thread called freeze_processes() and should not be frozen */
 
-#define PF_MEMALLOC_NOFS PF_FSTRANS     /* Transition to a more generic GFP_NOFS scope semantic */
-
 /*
  * Only the _current_ task can read/write to tsk->flags, but other
  * tasks can access tsk->flags in readonly mode for example
diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
index 830953ebb391..9daabe138c99 100644
--- a/include/linux/sched/mm.h
+++ b/include/linux/sched/mm.h
@@ -149,13 +149,21 @@ static inline bool in_vfork(struct task_struct *tsk)
         return ret;
 }
 
-/* __GFP_IO isn't allowed if PF_MEMALLOC_NOIO is set in current->flags
- * __GFP_FS is also cleared as it implies __GFP_IO.
+/*
+ * Applies per-task gfp context to the given allocation flags.
+ * PF_MEMALLOC_NOIO implies GFP_NOIO
+ * PF_MEMALLOC_NOFS implies GFP_NOFS
  */
-static inline gfp_t memalloc_noio_flags(gfp_t flags)
+static inline gfp_t current_gfp_context(gfp_t flags)
 {
+        /*
+         * NOIO implies both NOIO and NOFS and it is a weaker context
+         * so always make sure it makes precendence
+         */
         if (unlikely(current->flags & PF_MEMALLOC_NOIO))
                 flags &= ~(__GFP_IO | __GFP_FS);
+        else if (unlikely(current->flags & PF_MEMALLOC_NOFS))
+                flags &= ~__GFP_FS;
         return flags;
 }
 
@@ -171,4 +179,16 @@ static inline void memalloc_noio_restore(unsigned int flags)
         current->flags = (current->flags & ~PF_MEMALLOC_NOIO) | flags;
 }
 
+static inline unsigned int memalloc_nofs_save(void)
+{
+        unsigned int flags = current->flags & PF_MEMALLOC_NOFS;
+        current->flags |= PF_MEMALLOC_NOFS;
+        return flags;
+}
+
+static inline void memalloc_nofs_restore(unsigned int flags)
+{
+        current->flags = (current->flags & ~PF_MEMALLOC_NOFS) | flags;
+}
+
 #endif /* _LINUX_SCHED_MM_H */