fs: Convert nr_inodes and nr_unused to per-cpu counters

The number of inodes allocated does not need to be tied to the
addition or removal of an inode to/from a list. If we are not tied
to a list lock, we could update the counters when inodes are
initialised or destroyed, but to do that we need to convert the
counters to be per-cpu (i.e. independent of a lock). This means that
we have the freedom to change the list/locking implementation
without needing to care about the counters.

Based on a patch originally from Eric Dumazet.

[AV: cleaned up a bit, fixed build breakage on weird configs

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 2 insertions, 3 deletions

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 39f44f2e709a..f04d04af84f2 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -723,7 +723,7 @@ static long wb_check_old_data_flush(struct bdi_writeback *wb)
         wb->last_old_flush = jiffies;
         nr_pages = global_page_state(NR_FILE_DIRTY) +
                         global_page_state(NR_UNSTABLE_NFS) +
-                        (inodes_stat.nr_inodes - inodes_stat.nr_unused);
+                        get_nr_dirty_inodes();
 
         if (nr_pages) {
                 struct wb_writeback_work work = {
@@ -1090,8 +1090,7 @@ void writeback_inodes_sb(struct super_block *sb)
 
         WARN_ON(!rwsem_is_locked(&sb->s_umount));
 
-        work.nr_pages = nr_dirty + nr_unstable +
-                        (inodes_stat.nr_inodes - inodes_stat.nr_unused);
+        work.nr_pages = nr_dirty + nr_unstable + get_nr_dirty_inodes();
 
         bdi_queue_work(sb->s_bdi, &work);
         wait_for_completion(&done);