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A mirror of the official Linux kernel repository just in case
274052a2b0
Alexei Starovoitov says: ==================== Introduce any context BPF specific memory allocator. Tracing BPF programs can attach to kprobe and fentry. Hence they run in unknown context where calling plain kmalloc() might not be safe. Front-end kmalloc() with per-cpu cache of free elements. Refill this cache asynchronously from irq_work. Major achievements enabled by bpf_mem_alloc: - Dynamically allocated hash maps used to be 10 times slower than fully preallocated. With bpf_mem_alloc and subsequent optimizations the speed of dynamic maps is equal to full prealloc. - Tracing bpf programs can use dynamically allocated hash maps. Potentially saving lots of memory. Typical hash map is sparsely populated. - Sleepable bpf programs can used dynamically allocated hash maps. Future work: - Expose bpf_mem_alloc as uapi FD to be used in dynptr_alloc, kptr_alloc - Convert lru map to bpf_mem_alloc - Further cleanup htab code. Example: htab_use_raw_lock can be removed. Changelog: v5->v6: - Debugged the reason for selftests/bpf/test_maps ooming in a small VM that BPF CI is using. Added patch 16 that optimizes the usage of rcu_barrier-s between bpf_mem_alloc and hash map. It drastically improved the speed of htab destruction. v4->v5: - Fixed missing migrate_disable in hash tab free path (Daniel) - Replaced impossible "memory leak" with WARN_ON_ONCE (Martin) - Dropped sysctl kernel.bpf_force_dyn_alloc patch (Daniel) - Added Andrii's ack - Added new patch 15 that removes kmem_cache usage from bpf_mem_alloc. It saves memory, speeds up map create/destroy operations while maintains hash map update/delete performance. v3->v4: - fix build issue due to missing local.h on 32-bit arch - add Kumar's ack - proposal for next steps from Delyan: https://lore.kernel.org/bpf/d3f76b27f4e55ec9e400ae8dcaecbb702a4932e8.camel@fb.com/ v2->v3: - Rewrote the free_list algorithm based on discussions with Kumar. Patch 1. - Allowed sleepable bpf progs use dynamically allocated maps. Patches 13 and 14. - Added sysctl to force bpf_mem_alloc in hash map even if pre-alloc is requested to reduce memory consumption. Patch 15. - Fix: zero-fill percpu allocation - Single rcu_barrier at the end instead of each cpu during bpf_mem_alloc destruction v2 thread: https://lore.kernel.org/bpf/20220817210419.95560-1-alexei.starovoitov@gmail.com/ v1->v2: - Moved unsafe direct call_rcu() from hash map into safe place inside bpf_mem_alloc. Patches 7 and 9. - Optimized atomic_inc/dec in hash map with percpu_counter. Patch 6. - Tuned watermarks per allocation size. Patch 8 - Adopted this approach to per-cpu allocation. Patch 10. - Fully converted hash map to bpf_mem_alloc. Patch 11. - Removed tracing prog restriction on map types. Combination of all patches and final patch 12. v1 thread: https://lore.kernel.org/bpf/20220623003230.37497-1-alexei.starovoitov@gmail.com/ LWN article: https://lwn.net/Articles/899274/ ==================== Link: https://lore.kernel.org/r/ Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> |
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| README | ||
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.