llama: correct reverting of the entire batch.

also updates `llama_kv_cache_find_slot`, will correctly count the number of `used` cells for recurrent models

Author: Xarbirus

src/llama.cpp

@@ -2815,22 +2815,6 @@ struct llama_kv_cache {
     }
 };
 
-// saves the kv_cache state for future recovery
-// used to preserve the kv_cache state before searching for a slot
-struct llama_kv_slot_restorer {
-    struct llama_kv_cache_state {
-        uint32_t head = 0;
-        uint32_t size = 0;
-        uint32_t used = 0;
-        uint32_t n    = 0;
-    } old_state;
-
-    std::vector<llama_kv_cell> recurrent_cells;    // for     recurrent models only
-    std::pair<uint32_t, uint32_t> slot_boundaries; // for non-recurrent models only
-
-    bool restore = false;
-};
-
 struct llama_control_vector {
     std::vector<struct ggml_tensor *> tensors; // per layer
     std::vector<struct ggml_context *> ctxs;
@@ -3666,21 +3650,24 @@ static bool llama_kv_cache_init(
 // updates the cache head
 // Note: On success, it's important that cache.head points
 // to the first cell of the slot.
-static bool llama_kv_cache_find_slot(
+struct llama_kv_cache_slot_info {
+    std::pair<uint32_t, uint32_t> boundaries;
+    bool found = false;
+
+    explicit llama_kv_cache_slot_info(bool found_) : found{found_} {}
+    llama_kv_cache_slot_info(uint32_t begin, uint32_t end) : boundaries{begin, end}, found{true} {}
+
+    operator bool() const { return found; }
+};
+static const llama_kv_cache_slot_info llama_kv_cache_slot_info_failed{false};
+
+static struct llama_kv_cache_slot_info llama_kv_cache_find_slot(
            struct llama_kv_cache & cache,
-       const struct llama_ubatch & batch,
-   struct llama_kv_slot_restorer * slot_restorer = nullptr) {
+       const struct llama_ubatch & batch) {
     const uint32_t n_tokens = batch.n_tokens;
     const uint32_t n_seqs   = batch.n_seqs;
     const uint32_t n_seq_tokens = batch.n_seq_tokens;
 
-    if (slot_restorer != nullptr) {
-        slot_restorer->old_state.head  = cache.head;
-        slot_restorer->old_state.size  = cache.size;
-        slot_restorer->old_state.used  = cache.used;
-        slot_restorer->old_state.n     = cache.n;
-    }
-
     if (cache.recurrent) {
         // For recurrent state architectures (like Mamba or RWKV),
         // each cache cell can store the state for a whole sequence.
@@ -3689,11 +3676,6 @@ static bool llama_kv_cache_find_slot(
         // can only process batches with an equal number of new tokens in each sequence
         GGML_ASSERT(batch.equal_seqs);
 
-        if (slot_restorer != nullptr) {
-            slot_restorer->recurrent_cells = cache.cells;
-            slot_restorer->restore = true;
-        }
-
         int32_t min = cache.size - 1;
         int32_t max = 0;
 
@@ -3707,7 +3689,7 @@ static bool llama_kv_cache_find_slot(
                     // too big seq_id
                     // TODO: would it be possible to resize the cache instead?
                     LLAMA_LOG_ERROR("%s: seq_id=%d >= n_seq_max=%d Try using a bigger --parallel value\n", __func__, seq_id, cache.size);
-                    return false;
+                    return llama_kv_cache_slot_info_failed;
                 }
                 if (j > 0) {
                     llama_kv_cell & seq = cache.cells[seq_id];
@@ -3842,15 +3824,17 @@ static bool llama_kv_cache_find_slot(
         // allow getting the range of used cells, from head to head + n
         cache.head = min;
         cache.n    = max - min + 1;
+        cache.used = std::count_if(cache.cells.begin(), cache.cells.end(),
+            [](const llama_kv_cell& cell){ return !cell.is_empty(); });
 
         // sanity check
-        return cache.n >= n_seqs;
+        return llama_kv_cache_slot_info(cache.n >= n_seqs);
     }
     // otherwise, one cell per token.
 
     if (n_tokens > cache.size) {
         LLAMA_LOG_ERROR("%s: n_tokens=%d > cache.size=%d\n", __func__, n_tokens, cache.size);
-        return false;
+        return llama_kv_cache_slot_info_failed;
     }
 
     uint32_t n_tested = 0;
@@ -3878,15 +3862,10 @@ static bool llama_kv_cache_find_slot(
 
         if (n_tested >= cache.size) {
             //LLAMA_LOG_ERROR("%s: failed to find a slot for %d tokens\n", __func__, n_tokens);
-            return false;
+            return llama_kv_cache_slot_info_failed;
         }
     }
 
-    if (slot_restorer != nullptr) {
-        slot_restorer->slot_boundaries = std::make_pair(cache.head, cache.head + n_tokens);
-        slot_restorer->restore = true;
-    }
-
     for (uint32_t s = 0; s < n_seqs; s++) {
         for (uint32_t i = 0; i < n_seq_tokens; ++i) {
             uint32_t k = s*n_seq_tokens + i;
@@ -3900,7 +3879,7 @@ static bool llama_kv_cache_find_slot(
 
     cache.used += n_tokens;
 
-    return true;
+    return llama_kv_cache_slot_info(cache.head, cache.head + n_tokens);
 }
 
 // find how many cells are currently in use
@@ -4176,22 +4155,47 @@ static uint32_t llama_kv_cache_get_padding(const struct llama_cparams & cparams)
     return cparams.flash_attn ? 256u : 32u;
 }
 
-static void llama_kv_cache_slot_restore(
-        const struct llama_kv_slot_restorer & restorer,
-                      struct llama_kv_cache & cache) {
-    if (restorer.restore) {
-        cache.head  = restorer.old_state.head;
-        cache.size  = restorer.old_state.size;
-        cache.used  = restorer.old_state.used;
-        cache.n     = restorer.old_state.n;
-
-        if (cache.recurrent) {
-            cache.cells = restorer.recurrent_cells;
-        } else {
-            llama_kv_cache_seq_rm(cache, -1, restorer.slot_boundaries.first, restorer.slot_boundaries.second + 1);
+// saves the kv_cache state for future recovery.
+// used to rollback llama_kv_cache_find_slot changes.
+struct llama_kv_slot_restorer {
+    struct llama_kv_cache_state {
+        uint32_t head = 0;
+        uint32_t n    = 0;
+    } old_state;
+
+    std::vector<std::pair<uint32_t, uint32_t>> slot_boundaries; // for non-recurrent models only
+
+    bool do_restore = false;
+
+    explicit llama_kv_slot_restorer(const struct llama_kv_cache & cache) {
+        old_state.head  = cache.head;
+        old_state.n     = cache.n;
+    }
+
+    void save(const struct llama_kv_cache_slot_info& slot) {
+        if (slot) {
+            do_restore = true;
+            if (slot.boundaries.first != slot.boundaries.second) {
+                slot_boundaries.push_back(slot.boundaries);
+            }
         }
     }
-}
+
+    void restore(struct llama_kv_cache & cache) {
+        if (do_restore) {
+            cache.head  = old_state.head;
+            cache.n     = old_state.n;
+
+            if (cache.recurrent) { // recurrent models like Mamba or RWKV can't have a state partially erased
+                llama_kv_cache_seq_rm(cache, -1, -1, -1);
+            } else {
+                for (auto & slot : slot_boundaries) {
+                    llama_kv_cache_seq_rm(cache, -1, slot.first, slot.second);
+                }
+            }
+        }
+    }
+};
 
 //
 // model loading and saving
@@ -17235,7 +17239,7 @@ static int llama_decode_internal(
     lctx.n_queued_tokens += n_tokens_all;
 
     auto & kv_self = lctx.kv_self;
-    llama_kv_slot_restorer kv_slot_restorer;
+    llama_kv_slot_restorer kv_slot_restorer(kv_self);
 
     const int64_t n_embd  = hparams.n_embd;
     const int64_t n_vocab = hparams.n_vocab;
@@ -17320,9 +17324,11 @@ static int llama_decode_internal(
                 kv_self.head = 0;
             }
 
-            if (!llama_kv_cache_find_slot(kv_self, ubatch, &kv_slot_restorer)) {
+            const auto slot = llama_kv_cache_find_slot(kv_self, ubatch);
+            if (!slot) {
                 return 1;
             }
+            kv_slot_restorer.save(slot);
 
             if (!kv_self.recurrent) {
                 // a heuristic, to avoid attending the full cache if it is not yet utilized
@@ -17371,7 +17377,7 @@ static int llama_decode_internal(
 
         const auto compute_status = llama_graph_compute(lctx, gf, n_threads, threadpool);
         if (compute_status != GGML_STATUS_SUCCESS) {
-            llama_kv_cache_slot_restore(kv_slot_restorer, kv_self);
+            kv_slot_restorer.restore(kv_self);
             switch (compute_status) {
                 case GGML_STATUS_ABORTED:
                     return 2;