From 4e908332c4b47ae86796c35d4c1cdfa23799eb9e Mon Sep 17 00:00:00 2001
From: itigges22 <jitigges@vt.edu>
Date: Fri, 20 Mar 2026 17:12:49 -0400
Subject: [PATCH] fix: eviction logic for checkpoint creation during generation

The eviction was inside the is_empty() check, so it never ran when
all cells were occupied. Moved eviction outside to always try freeing
old checkpoints for new ones.

Results:
- 48 successful rollbacks (44% of rejections properly restored)
- 34.4 tok/s on short, ~20 tok/s on long generation
- 65% acceptance rate with proper rollback

Remaining: 56% of rejections still can't find checkpoints because
the checkpoint was evicted before seq_rm ran. Need to either keep
checkpoints longer or increase rs_size further.
---
 src/llama-memory-recurrent.cpp | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/src/llama-memory-recurrent.cpp b/src/llama-memory-recurrent.cpp
index fdcd54a292..c5e8eb5af7 100644
--- a/src/llama-memory-recurrent.cpp
+++ b/src/llama-memory-recurrent.cpp
@@ -707,9 +707,10 @@ bool llama_memory_recurrent::find_slot(const llama_ubatch & ubatch) {
             fprintf(stderr, "[MTP-FINDSLOT] checkpoint branch: seq_id=%d, cur_tail=%d, next_empty=%d\n",
                     (int)seq_id, cur_tail, (int)next_empty_cell);
             fflush(stderr);
-            if (next_empty_cell < size && cells[next_empty_cell].is_empty()) {
-                bool can_checkpoint = (get_cell_count(seq_id) < 8 && used < size * 0.9);
-                if (!can_checkpoint) {
+            {
+                bool can_checkpoint = (next_empty_cell < size && cells[next_empty_cell].is_empty() &&
+                                       get_cell_count(seq_id) < 8 && used < size * 0.9);
+                if (!can_checkpoint && get_cell_count(seq_id) >= 2) {
                     // Try to evict the oldest checkpoint to make room
                     int32_t oldest = -1;
                     llama_pos min_pos = std::numeric_limits<llama_pos>::max();
@@ -719,13 +720,19 @@ bool llama_memory_recurrent::find_slot(const llama_ubatch & ubatch) {
                             oldest = j;
                         }
                     }
+                    fprintf(stderr, "[MTP-FINDSLOT] eviction: oldest=%d (pos=%d), cur_tail=%d\n",
+                            oldest, (oldest >= 0 ? (int)cells[oldest].pos : -1), cur_tail);
+                    fflush(stderr);
                     if (oldest >= 0) {
                         cells[oldest].seq_id.erase(seq_id);
                         if (cells[oldest].is_empty()) {
                             cells[oldest].pos = -1;
                             cells[oldest].src = -1;
                             used--;
-                            next_empty_cell = oldest; // reuse the freed cell
+                            next_empty_cell = oldest;
+                            fprintf(stderr, "[MTP-FINDSLOT] evicted cell %d, next_empty=%d, used=%d\n",
+                                    oldest, (int)next_empty_cell, (int)used);
+                            fflush(stderr);
                         }
                         can_checkpoint = true;
                     }