mm: don't set __GFP_WRITE on ramfs/sysfs writes

There is not much point in skipping zones during allocation based on the
dirty usage which they'll never contribute to.  And we'd like to avoid
page reclaim waits when writing to ramfs/sysfs etc.

Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Greg Thelen <gthelen@google.com>
Cc: Ying Han <yinghan@google.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Acked-by: Minchan Kim <minchan.kim@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/filemap.c

@@ -2341,7 +2341,9 @@ struct page *grab_cache_page_write_begin(struct address_space *mapping,
 	struct page *page;
 	gfp_t gfp_notmask = 0;
 
-	gfp_mask = mapping_gfp_mask(mapping) | __GFP_WRITE;
+	gfp_mask = mapping_gfp_mask(mapping);
+	if (mapping_cap_account_dirty(mapping))
+		gfp_mask |= __GFP_WRITE;
 	if (flags & AOP_FLAG_NOFS)
 		gfp_notmask = __GFP_FS;
 repeat: