LU-11775 osc: reduce atomic ops in osc_enter_cache_try

We can reduce the number of atomic ops performed on
obd_dirty_pages for the common case.

Signed-off-by: Li Dongyang <dongyangli@ddn.com>
Change-Id: I5526e449d483241d825af18b612ae1d1dff3241e
Reviewed-on: https://review.whamcloud.com/33859
Tested-by: Jenkins
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Patrick Farrell <pfarrell@whamcloud.com>
Reviewed-by: Alexey Lyashkov <c17817@cray.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>

diff --git a/lustre/osc/osc_cache.c b/lustre/osc/osc_cache.c
index 67187c5..9984fc1 100644 (file)
--- a/lustre/osc/osc_cache.c
+++ b/lustre/osc/osc_cache.c
@@ -1403,7 +1403,6 @@ static void osc_consume_write_grant(struct client_obd *cli,
 {
        assert_spin_locked(&cli->cl_loi_list_lock);
        LASSERT(!(pga->flag & OBD_BRW_FROM_GRANT));
-       atomic_long_inc(&obd_dirty_pages);
        cli->cl_dirty_pages++;
        pga->flag |= OBD_BRW_FROM_GRANT;
        CDEBUG(D_CACHE, "using %lu grant credits for brw %p page %p\n",
@@ -1547,19 +1546,23 @@ static int osc_enter_cache_try(struct client_obd *cli,
        if (rc < 0)
                return 0;
 
-       if (cli->cl_dirty_pages < cli->cl_dirty_max_pages &&
-           1 + atomic_long_read(&obd_dirty_pages) <= obd_max_dirty_pages) {
-               osc_consume_write_grant(cli, &oap->oap_brw_page);
-               if (transient) {
-                       cli->cl_dirty_transit++;
-                       atomic_long_inc(&obd_dirty_transit_pages);
-                       oap->oap_brw_flags |= OBD_BRW_NOCACHE;
-               }
-               rc = 1;
-       } else {
-               __osc_unreserve_grant(cli, bytes, bytes);
-               rc = 0;
+       if (cli->cl_dirty_pages < cli->cl_dirty_max_pages) {
+               if (atomic_long_add_return(1, &obd_dirty_pages) <=
+                   obd_max_dirty_pages) {
+                       osc_consume_write_grant(cli, &oap->oap_brw_page);
+                       if (transient) {
+                               cli->cl_dirty_transit++;
+                               atomic_long_inc(&obd_dirty_transit_pages);
+                               oap->oap_brw_flags |= OBD_BRW_NOCACHE;
+                       }
+                       rc = 1;
+                       goto out;
+               } else
+                       atomic_long_dec(&obd_dirty_pages);
        }
+       __osc_unreserve_grant(cli, bytes, bytes);
+
+out:
        return rc;
 }