[PATCH 6/6] mm: Add memalloc_nowait

["Matthew Wilcox (Oracle)" <willy@infradead.org>]

Similar to memalloc_noio() and memalloc_nofs(), memalloc_nowait()
guarantees we will not sleep to reclaim memory.  Use it to simplify
dm-bufio's allocations.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 drivers/md/dm-bufio.c    | 30 ++++++++----------------------
 include/linux/sched.h    |  1 +
 include/linux/sched/mm.h | 12 ++++++++----
 3 files changed, 17 insertions(+), 26 deletions(-)

diff --git a/drivers/md/dm-bufio.c b/drivers/md/dm-bufio.c
index 6d1565021d74..140ada9a2c8f 100644
--- a/drivers/md/dm-bufio.c
+++ b/drivers/md/dm-bufio.c
@@ -412,23 +412,6 @@ static void *alloc_buffer_data(struct dm_bufio_client *c, gfp_t gfp_mask,
 
 	*data_mode = DATA_MODE_VMALLOC;
 
-	/*
-	 * __vmalloc allocates the data pages and auxiliary structures with
-	 * gfp_flags that were specified, but pagetables are always allocated
-	 * with GFP_KERNEL, no matter what was specified as gfp_mask.
-	 *
-	 * Consequently, we must set per-process flag PF_MEMALLOC_NOIO so that
-	 * all allocations done by this process (including pagetables) are done
-	 * as if GFP_NOIO was specified.
-	 */
-	if (gfp_mask & __GFP_NORETRY) {
-		unsigned noio_flag = memalloc_noio_save();
-		void *ptr = __vmalloc(c->block_size, gfp_mask);
-
-		memalloc_noio_restore(noio_flag);
-		return ptr;
-	}
-
 	return __vmalloc(c->block_size, gfp_mask);
 }
 
@@ -866,9 +849,6 @@ static struct dm_buffer *__alloc_buffer_wait_no_callback(struct dm_bufio_client
 	 * dm-bufio is resistant to allocation failures (it just keeps
 	 * one buffer reserved in cases all the allocations fail).
 	 * So set flags to not try too hard:
-	 *	GFP_NOWAIT: don't wait; if we need to sleep we'll release our
-	 *		    mutex and wait ourselves.
-	 *	__GFP_NORETRY: don't retry and rather return failure
 	 *	__GFP_NOMEMALLOC: don't use emergency reserves
 	 *	__GFP_NOWARN: don't print a warning in case of failure
 	 *
@@ -877,7 +857,9 @@ static struct dm_buffer *__alloc_buffer_wait_no_callback(struct dm_bufio_client
 	 */
 	while (1) {
 		if (dm_bufio_cache_size_latch != 1) {
-			b = alloc_buffer(c, GFP_NOWAIT | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN);
+			unsigned nowait_flag = memalloc_nowait_save();
+			b = alloc_buffer(c, GFP_KERNEL | __GFP_NOMEMALLOC | __GFP_NOWARN);
+			memalloc_nowait_restore(nowait_flag);
 			if (b)
 				return b;
 		}
@@ -886,8 +868,12 @@ static struct dm_buffer *__alloc_buffer_wait_no_callback(struct dm_bufio_client
 			return NULL;
 
 		if (dm_bufio_cache_size_latch != 1 && !tried_noio_alloc) {
+			unsigned noio_flag;
+
 			dm_bufio_unlock(c);
-			b = alloc_buffer(c, GFP_NOIO | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN);
+			noio_flag = memalloc_noio_save();
+			b = alloc_buffer(c, GFP_KERNEL | __GFP_NOMEMALLOC | __GFP_NOWARN);
+			memalloc_noio_restore(noio_flag);
 			dm_bufio_lock(c);
 			if (b)
 				return b;
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 90336850e940..b1c2cddd366c 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -803,6 +803,7 @@ struct task_struct {
 #endif
 	unsigned			memalloc_noio:1;
 	unsigned			memalloc_nofs:1;
+	unsigned			memalloc_nowait:1;
 	unsigned			memalloc_nocma:1;
 
 	unsigned long			atomic_flags; /* Flags requiring atomic access. */
diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
index 6f7b59a848a6..6484569f50df 100644
--- a/include/linux/sched/mm.h
+++ b/include/linux/sched/mm.h
@@ -179,12 +179,16 @@ static inline bool in_vfork(struct task_struct *tsk)
 static inline gfp_t current_gfp_context(gfp_t flags)
 {
 	if (unlikely(current->memalloc_noio || current->memalloc_nofs ||
-		     current->memalloc_nocma)) {
+		     current->memalloc_nocma) || current->memalloc_nowait) {
 		/*
-		 * NOIO implies both NOIO and NOFS and it is a weaker context
-		 * so always make sure it makes precedence
+		 * Clearing DIRECT_RECLAIM means we won't get to the point
+		 * of testing IO or FS, so we don't need to bother clearing
+		 * them.  noio implies neither IO nor FS and it is a weaker
+		 * context so always make sure it takes precedence.
 		 */
-		if (current->memalloc_noio)
+		if (current->memalloc_nowait)
+			flags &= ~__GFP_DIRECT_RECLAIM;
+		else if (current->memalloc_noio)
 			flags &= ~(__GFP_IO | __GFP_FS);
 		else if (current->memalloc_nofs)
 			flags &= ~__GFP_FS;
-- 
2.27.0