kv-cache : SWA checkpoints store only non-masked cells (#23981)

Author: ggerganov

src/llama-kv-cache.cpp

@@ -1876,7 +1876,19 @@ void llama_kv_cache::state_write(llama_io_write_i & io, llama_seq_id seq_id, lla
         uint32_t cell_range_begin = cells.size();
 
         for (uint32_t i = 0; i < cells.size(); ++i) {
-            if (!cells.is_empty(i) && (seq_id == -1 || cells.seq_has(i, seq_id))) {
+            bool add_cell = true;
+
+            add_cell = add_cell && !cells.is_empty(i);
+            add_cell = add_cell && (seq_id == -1 || cells.seq_has(i, seq_id));
+
+            // check the cell is not SWA-masked
+            if (add_cell && seq_id != -1) {
+                const bool is_masked = llama_hparams::is_masked_swa(n_swa, swa_type, cells.pos_get(i), cells.seq_pos_max(seq_id));
+
+                add_cell = !is_masked;
+            }
+
+            if (add_cell) {
                 ++cell_count;
                 if (cell_range_begin == cells.size()) {
                     cell_range_begin = i;
@@ -2129,7 +2141,7 @@ bool llama_kv_cache::state_read_meta(llama_io_read_i & io, uint32_t strm, uint32
 
         sinfo = find_slot(ubatch, false);
         if (sinfo.empty()) {
-            LLAMA_LOG_ERROR("%s: failed to find available cells in kv cache\n", __func__);
+            LLAMA_LOG_ERROR("%s: failed to find %d available cells in kv cache\n", __func__,  cell_count);
             return false;
         }