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diff --git a/doc/dev/mempool_accounting.rst b/doc/dev/mempool_accounting.rst new file mode 100644 index 000000000..d86220ae8 --- /dev/null +++ b/doc/dev/mempool_accounting.rst @@ -0,0 +1,49 @@ +What is a mempool? +------------------ +A memory pool (mempool) is a method for tracking memory consumption. Memory pools represent the memory consumption +of C++ classes and containers, and they are used to assess memory leaks and other insights around memory usage with +low overhead. Each memory pool tracks the number of bytes and items it contains. Mempools are statically declared, +and they serve the purpose of identifying memory-related checks in BlueStore. + +Some common mempools that we can track +-------------------------------------- + +- ``bloom_filter``: tracks objects already in the cache pool in order to determine which objects in the pool are + being accessed +- ``bluestore_alloc``: accounts for actual allocations done by an allocator +- ``bluestore_inline_bl``: measures encoded length of an inline buffer +- ``bluestore_fsck``: file system consistency check for BlueStore metadata; helps in tracking and debugging during OSD repairs +- ``bluestore_txc``: accounts for committed transactions counter +- ``bluestore_writing_deferred``: measures small writes which are deferred, i.e. first written into RocksDB WAL and later + flushed to the disk +- ``bluestore_writing``: accounts for in-flight write buffers +- ``bluefs``: file-system-like interface; provides just enough functionality to allow RocksDB to store its “files” and share + the same raw device(s) with BlueStore +- ``buffer_anon``: stores arbitrary buffer data +- ``buffer_meta``: all the metadata associated with buffer anon buffers +- ``bluestore_cache_data``: mempool for writing and writing deferred +- ``bluestore_cache_onode``: object node (onode) metadata in the BlueStore cache +- ``bluestore_cache_meta``: key under PREFIX_OBJ where we are stored +- ``bluestore_cache_other``: right now accounts for: + + - ``map_t``: used to track raw extents on disk for SharedBlob and for the in-memory Blob with the blob namespace + - ``coll_map``: collections_map + - ``csum_data``: checksum data +- ``bluestore_cache_buffer``: accounts for buffer cache shards +- ``bluestore_extent``: a logical (as well as physical) extent, pointing to some portion of a blob +- ``bluestore_blob``: in-memory blob metadata associated cached buffers +- ``bluestore_shared_blob``: in-memory shared blob state; stores a reference to the set of collections it belongs to + (includes cached buffers) +- ``bluefs_file_reader``: accounts for bluefs file reader buffer +- ``bluefs_file_writer``: accounts for bluefs file writer buffer + +Check mempools usage +~~~~~~~~~~~~~~~~~~~~ + +Command to see BlueStore memory allocation in these mempools:: + + $ ceph daemon osd.NNN dump_mempools + + +.. note:: see more: + https://github.com/ceph/ceph/blob/main/src/include/mempool.h |