+/**
+ * Atomic operations are expensive. We accumulate the accounting for the
+ * same page zone to get better performance.
+ * In practice this can work pretty good because the pages in the same RPC
+ * are likely from the same page zone.
+ */
+static inline void unstable_page_accounting(struct ptlrpc_bulk_desc *desc,
+ int factor)
+{
+ obd_count page_count = desc->bd_iov_count;
+ void *zone = NULL;
+ int count = 0;
+ int i;
+
+ for (i = 0; i < page_count; i++) {
+ void *pz = page_zone(desc->bd_iov[i].kiov_page);
+
+ if (likely(pz == zone)) {
+ ++count;
+ continue;
+ }
+
+ if (count > 0) {
+ mod_zone_page_state(zone, NR_UNSTABLE_NFS,
+ factor * count);
+ count = 0;
+ }
+ zone = pz;
+ ++count;
+ }
+ if (count > 0)
+ mod_zone_page_state(zone, NR_UNSTABLE_NFS, factor * count);
+}
+
+static inline void add_unstable_page_accounting(struct ptlrpc_bulk_desc *desc)
+{
+ unstable_page_accounting(desc, 1);
+}
+
+static inline void dec_unstable_page_accounting(struct ptlrpc_bulk_desc *desc)
+{
+ unstable_page_accounting(desc, -1);
+}
+
+/**
+ * Performs "unstable" page accounting. This function balances the
+ * increment operations performed in osc_inc_unstable_pages. It is
+ * registered as the RPC request callback, and is executed when the
+ * bulk RPC is committed on the server. Thus at this point, the pages
+ * involved in the bulk transfer are no longer considered unstable.
+ *
+ * If this function is called, the request should have been committed
+ * or req:rq_unstable must have been set; it implies that the unstable
+ * statistic have been added.
+ */
+void osc_dec_unstable_pages(struct ptlrpc_request *req)
+{
+ struct ptlrpc_bulk_desc *desc = req->rq_bulk;
+ struct client_obd *cli = &req->rq_import->imp_obd->u.cli;
+ obd_count page_count = desc->bd_iov_count;
+ int unstable_count;
+
+ LASSERT(page_count >= 0);
+ dec_unstable_page_accounting(desc);
+
+ unstable_count = atomic_sub_return(page_count, &cli->cl_unstable_count);
+ LASSERT(unstable_count >= 0);
+
+ unstable_count = atomic_sub_return(page_count,
+ &cli->cl_cache->ccc_unstable_nr);
+ LASSERT(unstable_count >= 0);
+ if (unstable_count == 0)
+ wake_up_all(&cli->cl_cache->ccc_unstable_waitq);
+
+ if (osc_cache_too_much(cli))
+ (void)ptlrpcd_queue_work(cli->cl_lru_work);
+}
+
+/**
+ * "unstable" page accounting. See: osc_dec_unstable_pages.
+ */
+void osc_inc_unstable_pages(struct ptlrpc_request *req)
+{
+ struct ptlrpc_bulk_desc *desc = req->rq_bulk;
+ struct client_obd *cli = &req->rq_import->imp_obd->u.cli;
+ obd_count page_count = desc->bd_iov_count;
+
+ /* No unstable page tracking */
+ if (cli->cl_cache == NULL || !cli->cl_cache->ccc_unstable_check)
+ return;
+
+ add_unstable_page_accounting(desc);
+ atomic_add(page_count, &cli->cl_unstable_count);
+ atomic_add(page_count, &cli->cl_cache->ccc_unstable_nr);
+
+ /* If the request has already been committed (i.e. brw_commit
+ * called via rq_commit_cb), we need to undo the unstable page
+ * increments we just performed because rq_commit_cb wont be
+ * called again. */
+ spin_lock(&req->rq_lock);
+ if (unlikely(req->rq_committed)) {
+ spin_unlock(&req->rq_lock);
+
+ osc_dec_unstable_pages(req);
+ } else {
+ req->rq_unstable = 1;
+ spin_unlock(&req->rq_lock);
+ }
+}
+
+/**
+ * Check if it piggybacks SOFT_SYNC flag to OST from this OSC.
+ * This function will be called by every BRW RPC so it's critical
+ * to make this function fast.
+ */
+bool osc_over_unstable_soft_limit(struct client_obd *cli)
+{
+ long unstable_nr, osc_unstable_count;
+
+ /* Can't check cli->cl_unstable_count, therefore, no soft limit */
+ if (cli->cl_cache == NULL || !cli->cl_cache->ccc_unstable_check)
+ return false;
+
+ osc_unstable_count = atomic_read(&cli->cl_unstable_count);
+ unstable_nr = atomic_read(&cli->cl_cache->ccc_unstable_nr);
+
+ CDEBUG(D_CACHE,
+ "%s: cli: %p unstable pages: %lu, osc unstable pages: %lu\n",
+ cli->cl_import->imp_obd->obd_name, cli,
+ unstable_nr, osc_unstable_count);
+
+ /* If the LRU slots are in shortage - 25% remaining AND this OSC
+ * has one full RPC window of unstable pages, it's a good chance
+ * to piggyback a SOFT_SYNC flag.
+ * Please notice that the OST won't take immediate response for the
+ * SOFT_SYNC request so active OSCs will have more chance to carry
+ * the flag, this is reasonable. */
+ return unstable_nr > cli->cl_cache->ccc_lru_max >> 2 &&
+ osc_unstable_count > cli->cl_max_pages_per_rpc *
+ cli->cl_max_rpcs_in_flight;
+}
+