Prefix caching for PagedAttention

[EricLBuehler]

• [x] Prefix cacher handles pagedattention seqs
• [x] Updated sequence logic
• [ ] Updated inputs processing

Currently not working yet.

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📥 Commits

Reviewing files that changed from the base of the PR and between 01cedfa0921b39f574b8a98c0a554b86676563dd and 378487667c297db3e050abbc3a464a1777b3ee8e.

📒 Files selected for processing (1)

• docs/PAGED_ATTENTION.md (1 hunks)

Walkthrough

This update refactors the PagedAttention and block engine infrastructure to remove explicit lifetime annotations, replacing mutable references with thread-safe, shared ownership via Arc<Mutex<_>>. It introduces new block-based caching mechanisms, updates method signatures for concurrency, and enhances block management. The changes propagate through input processors, sequence management, schedulers, and cache handling, unifying interfaces and improving modularity.

Changes

File(s)	Change Summary
src/pipeline/inputs_processor.rs, src/pipeline/mod.rs, src/pipeline/speculative.rs, src/pipeline/speech.rs, src/vision_models/*/inputs_processor.rs	Removed lifetime parameters from PagedAttentionMeta and related method signatures; updated handling to use owned/shared types.
src/paged_attention/block_engine.rs, src/dummy_paged_attention/block_engine.rs	Added Debug, Clone, and Hash to LogicalTokenBlock; added accessors; enhanced allocation logic to support prefilled blocks; fixed CPU allocator flag.
src/paged_attention/block_engine_sequence.rs, src/dummy_paged_attention/block_engine_sequence.rs	Changed trait method to return slice of logical blocks; added method for taking prefilled physical blocks.
src/paged_attention/mod.rs, src/dummy_paged_attention/mod.rs	Publicly re-exported PhysicalTokenBlock; implemented cache configuration logic.
src/paged_attention/scheduler.rs, src/dummy_paged_attention/scheduler.rs	Wrapped BlockEngine in Arc<Mutex<_>>; updated all usages to lock for thread safety; updated method signatures for concurrency.
src/scheduler/mod.rs, src/scheduler/default_scheduler.rs	Changed scheduler trait methods to return owned or shared types instead of references; updated for thread safety.
src/engine/add_request.rs, src/engine/mod.rs	Updated prefix cache handling to support both normal and paged (block-based) cache variants; improved scheduler/block engine initialization.
src/sequence.rs	Added support for physical token blocks in paged attention metadata; added prefill methods; refactored token-to-block logic; updated block engine sequence trait implementation.
src/prefix_cacher.rs	Introduced block-based prefix caching; added new cache structures and lookup logic; updated cache manager to support both token and block-based caches.
src/diffusion_models/processor.rs	Updated method signatures to remove lifetimes from paged attention metadata.
src/vision_models/*/inputs_processor.rs	Updated input processor method signatures to accept owned paged attention metadata.
mistralrs-quant/src/metal_kernels/mod.rs, mistralrs-quant/src/utils/ops.rs	Replaced manual ceiling division with div_ceil; minor optimizations and signature simplification.

Sequence Diagram(s)

sequenceDiagram
    participant Client
    participant Scheduler
    participant BlockEngine
    participant PrefixCacheManager
    participant Sequence

    Client->>Scheduler: Add request (with tokens)
    Scheduler->>PrefixCacheManager: search_for_matching_cache(tokens)
    alt Block-based cache enabled
        PrefixCacheManager->>BlockEngine: Get logical/physical blocks
        PrefixCacheManager-->>Scheduler: Return MatchingCache::Paged
    else
        PrefixCacheManager-->>Scheduler: Return MatchingCache::Normal
    end
    Scheduler->>BlockEngine: allocate(mut Sequence)
    BlockEngine->>Sequence: assign blocks (may use prefilled)
    Scheduler->>Sequence: prefill_v2_normal or prefill_v2_paged
    Sequence-->>Scheduler: Sequence ready

Poem

In fields of memory, blocks align,
With mutex guards, their fates entwine.
No lifetimes chase the rabbits here—
Just shared Arc paths, all crystal clear!
Caches leap, and tokens bound,
Prefilled blocks are hopping 'round.
🐇✨ Rusty dreams, concurrency found!

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[github-actions[bot]]

Code Metrics Report

===============================================================================
 Language            Files        Lines         Code     Comments       Blanks
===============================================================================
 C Header                3           62           53            0            9
 CSS                     1          428          366           12           50
 Dockerfile              1           41           22           10            9
 HTML                    1           58           46            4            8
 JavaScript              7         1221          915          169          137
 JSON                   12          107          106            0            1
 Makefile                1            6            5            0            1
 Python                 86         4046         3414          158          474
 Shell                   1           63           26           18           19
 Plain Text              3         3723            0         2413         1310
 TOML                   20          607          549           10           48
 YAML                    2           21           19            2            0
-------------------------------------------------------------------------------
 Jupyter Notebooks       3            0            0            0            0
 |- Markdown             2           77           32           31           14
 |- Python               2          205          178            1           26
 (Total)                            282          210           32           40
-------------------------------------------------------------------------------
 Markdown               56         4932            0         3761         1171
 |- BASH                 9           99           96            0            3
 |- JSON                 1           12           12            0            0
 |- Python               7          121          109            0           12
 |- Rust                22          757          634            1          122
 |- TOML                 2           75           63            0           12
 (Total)                           5996          914         3762         1320
-------------------------------------------------------------------------------
 Rust                  386       130170       116052         2765        11353
 |- Markdown           178         2235           29         1996          210
 (Total)                         132405       116081         4761        11563
===============================================================================
 Total                 583       145485       121573         9322        14590
===============================================================================