mm: convert i_mmap_mutex to rwsem

The i_mmap_mutex is a close cousin of the anon vma lock, both protecting
similar data, one for file backed pages and the other for anon memory.  To
this end, this lock can also be a rwsem.  In addition, there are some
important opportunities to share the lock when there are no tree
modifications.

This conversion is straightforward.  For now, all users take the write
lock.

[sfr@canb.auug.org.au: update fremap.c]
Signed-off-by: Davidlohr Bueso <dbueso@suse.de>
Reviewed-by: Rik van Riel <riel@redhat.com>
Acked-by: "Kirill A. Shutemov" <kirill@shutemov.name>
Acked-by: Hugh Dickins <hughd@google.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Acked-by: Mel Gorman <mgorman@suse.de>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 3 deletions

diff --git a/include/linux/fs.h b/include/linux/fs.h
index bd0a1b2f3c02..6abcd0b72ae0 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -18,6 +18,7 @@
 #include <linux/pid.h>
 #include <linux/bug.h>
 #include <linux/mutex.h>
+#include <linux/rwsem.h>
 #include <linux/capability.h>
 #include <linux/semaphore.h>
 #include <linux/fiemap.h>
@@ -401,7 +402,7 @@ struct address_space {
         atomic_t                i_mmap_writable;/* count VM_SHARED mappings */
         struct rb_root          i_mmap;         /* tree of private and shared mappings */
         struct list_head        i_mmap_nonlinear;/*list VM_NONLINEAR mappings */
-        struct mutex            i_mmap_mutex;   /* protect tree, count, list */
+        struct rw_semaphore     i_mmap_rwsem;   /* protect tree, count, list */
         /* Protected by tree_lock together with the radix tree */
         unsigned long           nrpages;        /* number of total pages */
         unsigned long           nrshadows;      /* number of shadow entries */
@@ -469,12 +470,12 @@ int mapping_tagged(struct address_space *mapping, int tag);
 
 static inline void i_mmap_lock_write(struct address_space *mapping)
 {
-        mutex_lock(&mapping->i_mmap_mutex);
+        down_write(&mapping->i_mmap_rwsem);
 }
 
 static inline void i_mmap_unlock_write(struct address_space *mapping)
 {
-        mutex_unlock(&mapping->i_mmap_mutex);
+        up_write(&mapping->i_mmap_rwsem);
 }
 
 /*