Make arc_need_free updates atomic

Ensures proper accounting of bytes we requested to free

AKAMAI: zfs: CR 3695072
Reviewed-by: Tim Chase <tim@chase2k.com>
Reviewed-by: Richard Yao <ryao@gentoo.org>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Debabrata Banerjee <dbanerje@akamai.com>
Issue #6035

diff --git a/module/zfs/arc.c b/module/zfs/arc.c
index 4e5c9eaf509c5f2330edfa1b60fcdf00fd65c386..fa69e1ea4edb0c1d9a4492cf00c00712d33bc3e9 100644 (file)
--- a/module/zfs/arc.c
+++ b/module/zfs/arc.c
@@ -4220,7 +4220,7 @@ arc_reclaim_thread(void)
        while (!arc_reclaim_thread_exit) {
                int64_t to_free;
                uint64_t evicted = 0;
-
+               uint64_t need_free = arc_need_free;
                arc_tuning_update();
 
                /*
@@ -4270,7 +4270,7 @@ arc_reclaim_thread(void)
                        to_free = (arc_c >> arc_shrink_shift) - free_memory;
                        if (to_free > 0) {
 #ifdef _KERNEL
-                               to_free = MAX(to_free, arc_need_free);
+                               to_free = MAX(to_free, need_free);
 #endif
                                arc_shrink(to_free);
                        }
@@ -4295,11 +4295,12 @@ arc_reclaim_thread(void)
                        /*
                         * We're either no longer overflowing, or we
                         * can't evict anything more, so we should wake
-                        * up any threads before we go to sleep and clear
-                        * arc_need_free since nothing more can be done.
+                        * up any threads before we go to sleep and remove
+                        * the bytes we were working on from arc_need_free
+                        * since nothing more will be done here.
                         */
                        cv_broadcast(&arc_reclaim_waiters_cv);
-                       arc_need_free = 0;
+                       ARCSTAT_INCR(arcstat_need_free, -need_free);
 
                        /*
                         * Block until signaled, or after one second (we
@@ -4452,7 +4453,7 @@ __arc_shrinker_func(struct shrinker *shrink, struct shrink_control *sc)
                ARCSTAT_BUMP(arcstat_memory_indirect_count);
        } else {
                arc_no_grow = B_TRUE;
-               arc_need_free = ptob(sc->nr_to_scan);
+               ARCSTAT_INCR(arcstat_need_free, ptob(sc->nr_to_scan));
                ARCSTAT_BUMP(arcstat_memory_direct_count);
        }