[PATCH v2 03/13] mm: Add support for async buffered writes

[Stefan Roesch <shr@fb.com>]

This adds support for async buffered writes in the mm layer. When the
AOP_FLAG_NOWAIT flag is set, if the page is not already loaded,
the page gets created without blocking on the allocation.

Signed-off-by: Stefan Roesch <shr@fb.com>
---
 mm/filemap.c      |  1 +
 mm/folio-compat.c | 12 ++++++++++--
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index 5bd692a327d0..f4e2036c5029 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -42,6 +42,7 @@
 #include <linux/ramfs.h>
 #include <linux/page_idle.h>
 #include <linux/migrate.h>
+#include <linux/sched/mm.h>
 #include <asm/pgalloc.h>
 #include <asm/tlbflush.h>
 #include "internal.h"
diff --git a/mm/folio-compat.c b/mm/folio-compat.c
index 749555a232a8..8243eeb883c1 100644
--- a/mm/folio-compat.c
+++ b/mm/folio-compat.c
@@ -133,11 +133,19 @@ struct page *grab_cache_page_write_begin(struct address_space *mapping,
 					pgoff_t index, unsigned flags)
 {
 	unsigned fgp_flags = FGP_LOCK | FGP_WRITE | FGP_CREAT | FGP_STABLE;
+	gfp_t gfp = mapping_gfp_mask(mapping);
 
 	if (flags & AOP_FLAG_NOFS)
 		fgp_flags |= FGP_NOFS;
-	return pagecache_get_page(mapping, index, fgp_flags,
-			mapping_gfp_mask(mapping));
+
+	if (flags & AOP_FLAG_NOWAIT) {
+		fgp_flags |= FGP_NOWAIT;
+
+		gfp |= GFP_ATOMIC;
+		gfp &= ~__GFP_DIRECT_RECLAIM;
+	}
+
+	return pagecache_get_page(mapping, index, fgp_flags, gfp);
 }
 EXPORT_SYMBOL(grab_cache_page_write_begin);
 
-- 
2.30.2