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patch(paged) 0002: LLAMA_KV_PAGED block placement, Gate 0 token-identical

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find_slot places a sequence's tokens at permuted non-contiguous blocks; greedy
generation is token-identical to stock (verified on Qwen3-0.6B at the pin),
branch confirmed firing. Default off. The placement substrate for the gather-read.

Assisted-by: Claude:opus-4.8 [Claude Code]
Signed-off-by: Ettore Di Giacinto <mudler@localai.io>
This commit is contained in:
Ettore Di Giacinto
2026-06-19 23:04:28 +00:00
parent ce48cc0751
commit 61ff738177
1 changed files with 75 additions and 0 deletions
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75
backend/cpp/llama-cpp/patches/0002-paged-kv-block-placement-env-LLAMA_KV_PAGED.patch Normal file
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@@ -0,0 +1,75 @@
From 5c9c709e6c6b07e0399b75fd4e46e752d418a9a8 Mon Sep 17 00:00:00 2001
From: Ettore Di Giacinto <mudler@localai.io>
Date: Fri, 19 Jun 2026 23:04:17 +0000
Subject: [PATCH] paged kv block placement (env LLAMA_KV_PAGED)
Place each sequence's tokens at permuted, non-contiguous fixed-size block
positions in find_slot, proving attention is invariant to physical KV placement
(token-identical greedy generation). Default off; single-sequence scope; falls
back to the normal allocator. The paged-placement substrate for the gather-read.
---
src/llama-kv-cache.cpp | 41 +++++++++++++++++++++++++++++++++++++++++
1 file changed, 41 insertions(+)
diff --git a/src/llama-kv-cache.cpp b/src/llama-kv-cache.cpp
index 2802103bd..999e2ae61 100644
--- a/src/llama-kv-cache.cpp
+++ b/src/llama-kv-cache.cpp
@@ -11,6 +11,8 @@
#include <cstring>
#include <limits>
#include <map>
+#include <numeric>
+#include <cstdlib>
#include <stdexcept>
static bool ggml_is_power_of_2(int n) {
@@ -1020,6 +1022,45 @@ llama_kv_cache::slot_info llama_kv_cache::find_slot(const llama_ubatch & ubatch,
return { };
}
+ // [paged, experimental] Place this sequence's tokens at permuted,
+ // non-contiguous fixed-size BLOCK positions instead of a contiguous run.
+ // This validates that attention is invariant to physical KV placement -
+ // the correctness premise of paged attention. Enabled via LLAMA_KV_PAGED.
+ // Single-sequence scope (uses get_used() as the logical base); falls back
+ // to the normal allocator if the permuted cells aren't available.
+ static const bool paged_mode = (std::getenv("LLAMA_KV_PAGED") != nullptr);
+ if (paged_mode) {
+ const uint32_t bs = 16; // block size (tokens/block)
+ const uint32_t nblk = cells.size() / bs; // blocks in this stream's pool
+ if (nblk >= 2) {
+ // stride coprime to nblk => block-index permutation is a bijection
+ uint32_t k = 1;
+ for (uint32_t cand = (nblk / 2) | 1u; cand < nblk; cand += 2) {
+ if (std::gcd(cand, nblk) == 1u) { k = cand; break; }
+ }
+ const uint32_t base = cells.get_used();
+ bool ok = true;
+ for (uint32_t i = 0; i < n_tokens; ++i) {
+ const uint32_t L = base + i;
+ const uint32_t b = L / bs;
+ const uint32_t off = L % bs;
+ if (b >= nblk) { ok = false; break; }
+ const uint32_t phys = ((b * k) % nblk) * bs + off; // permuted block
+ if (phys >= cells.size() || !cells.is_empty(phys)) { ok = false; break; }
+ res.idxs[s].push_back(phys);
+ }
+ if (ok && res.idxs[s].size() == n_tokens) {
+ if (std::getenv("LLAMA_KV_PAGED_DEBUG")) {
+ fprintf(stderr, "[paged] seq placed %u tok at cells:", n_tokens);
+ for (uint32_t z = 0; z < res.idxs[s].size() && z < 24; ++z) fprintf(stderr, " %u", res.idxs[s][z]);
+ fprintf(stderr, " (k=%u nblk=%u base=%u)\n", k, nblk, base);
+ }
+ continue; // paged placement succeeded for this sequence
+ }
+ res.idxs[s].clear(); // fall back to the normal allocator
+ }
+ }
+
uint32_t n_tested = 0;
// for continuous slots, we test that all tokens in the ubatch fit, starting from the current head
--
2.43.0