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125d10a782
Fixes the paged-pool burst-degradation bug (OTHER_PATHS_INVESTIGATION.md section C Part 2): on a long-lived llama-server with LLAMA_KV_PAGED=1, a high-fan-out prefill burst strands KV blocks in the host-side paged pool, so a later lower-npl prefill draws from a depleted/fragmented pool and its throughput collapses (the benchmark's "restart per npl" crutch). Decode is unaffected. The fix changes only host-side block accounting and placement, never KV values or compute, and is gated behind LLAMA_KV_PAGED (LLAMA_PAGED_NO_RECLAIM=1 restores the pre-fix behavior). Fix-1 reclaim trailing blocks: PagedKVManager::truncate(seq, n_keep) frees every block beyond ceil(n_keep/bs) (ref-counted); called from llama_kv_cache::seq_rm for the p1==MAX && p0>0 partial-tail case so the manager tracks the kv-cache exactly. Fix-2 defrag on empty: when the pool is fully idle, defrag_free_pool() relinks the free queue into ascending block-id order (FreeBlockQueue::rebuild), preserving content-cache hashes. Fix-3 release on slot completion: server_slot::release() issues prompt_clear() under the paged engine so a finished-idle slot returns its blocks promptly. Validation (DGX GB10, q36-27b-nvfp4 = qwen35 hybrid; HEAD f7409c2 = patch 0023): - Bit-exact: greedy md5 identical across paged off / paged on / paged on+NO_RECLAIM (5951a5b4d624ce891e22ab5fca9bc439), == the 0023 baseline. test-backend-ops unaffected (no ggml op touched). - Host unit test: truncate reclaims exactly 16 trailing blocks; defrag restores ascending popleft order. UNIT PASS. - Model A/B (one binary, NO_RECLAIM): fragmentation prefill ratio 0.944 -> 0.998; 64 idle slots strand 2048 blocks, reclaim returns the pool to fresh (2527). - Server A/B (FRESH-npl8 -> BURST-npl64 -> POST-npl8): POST-npl8 prefill collapses 488 -> 44 t/s with NO_RECLAIM (the bug; investigation saw 507 -> 65), restored to 532 t/s (fresh 525, within 1%) with the fix. Paged release-log count 17 -> 96 (Fix-3 fires per slot completion). Canary tokens identical fresh-vs-post in both arms (bit-exact serving). Assisted-by: Claude:opus-4.8 [Claude Code] Signed-off-by: Ettore Di Giacinto <mudler@localai.io>
