mm/filemap.c: rewrite mapping_needs_writeback in less fancy manner

This actually checks that writeback is needed or in progress.

Link: http://lkml.kernel.org/r/156378817069.1087.1302816672037672488.stgit@buzz
Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jan Kara <jack@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 5 insertions, 2 deletions

diff --git a/mm/filemap.c b/mm/filemap.c
index 82f3b9a3a940..d5462d706f76 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -618,10 +618,13 @@ int filemap_fdatawait_keep_errors(struct address_space *mapping)
 }
 EXPORT_SYMBOL(filemap_fdatawait_keep_errors);
 
+/* Returns true if writeback might be needed or already in progress. */
 static bool mapping_needs_writeback(struct address_space *mapping)
 {
-        return (!dax_mapping(mapping) && mapping->nrpages) ||
-            (dax_mapping(mapping) && mapping->nrexceptional);
+        if (dax_mapping(mapping))
+                return mapping->nrexceptional;
+
+        return mapping->nrpages;
 }
 
 int filemap_write_and_wait(struct address_space *mapping)