ceph/doc/dev/mempool_accounting.rst

   1 What is a mempool?
   2 ------------------
   3 A memory pool (mempool) is a method for tracking memory consumption. Memory pools represent the memory consumption
   4 of C++ classes and containers, and they are used to assess memory leaks and other insights around memory usage with
   5 low overhead. Each memory pool tracks the number of bytes and items it contains. Mempools are statically declared,
   6 and they serve the purpose of identifying memory-related checks in BlueStore.
   7
   8 Some common mempools that we can track
   9 --------------------------------------
  10
  11 - ``bloom_filter``: tracks objects already in the cache pool in order to determine which objects in the pool are
  12   being accessed
  13 - ``bluestore_alloc``: accounts for actual allocations done by an allocator
  14 - ``bluestore_inline_bl``: measures encoded length of an inline buffer
  15 - ``bluestore_fsck``: file system consistency check for BlueStore metadata; helps in tracking and debugging during OSD repairs
  16 - ``bluestore_txc``: accounts for committed transactions counter
  17 - ``bluestore_writing_deferred``: measures small writes which are deferred, i.e. first written into RocksDB WAL and later
  18   flushed to the disk
  19 - ``bluestore_writing``: accounts for in-flight write buffers
  20 - ``bluefs``:  file-system-like interface; provides just enough functionality to allow RocksDB to store its “files” and share
  21   the same raw device(s) with BlueStore
  22 - ``buffer_anon``: stores arbitrary buffer data
  23 - ``buffer_meta``: all the metadata associated with buffer anon buffers
  24 - ``bluestore_cache_data``: mempool for writing and writing deferred
  25 - ``bluestore_cache_onode``: object node (onode) metadata in the BlueStore cache
  26 - ``bluestore_cache_meta``: key under PREFIX_OBJ where we are stored
  27 - ``bluestore_cache_other``: right now accounts for:
  28
  29   - ``map_t``: used to track raw extents on disk for SharedBlob and for the in-memory Blob with the blob namespace
  30   - ``coll_map``: collections_map
  31   - ``csum_data``: checksum data
  32 - ``bluestore_cache_buffer``: accounts for buffer cache shards
  33 - ``bluestore_extent``: a logical (as well as physical) extent, pointing to some portion of a blob
  34 - ``bluestore_blob``: in-memory blob metadata associated cached buffers
  35 - ``bluestore_shared_blob``: in-memory shared blob state; stores a reference to the set of collections it belongs to
  36   (includes cached buffers)
  37 - ``bluefs_file_reader``: accounts for bluefs file reader buffer
  38 - ``bluefs_file_writer``: accounts for bluefs file writer buffer
  39
  40 Check mempools usage
  41 ~~~~~~~~~~~~~~~~~~~~
  42
  43 Command to see BlueStore memory allocation in these mempools::
  44
  45      $ ceph daemon osd.NNN dump_mempools
  46
  47
  48 .. note:: see more:
  49     https://github.com/ceph/ceph/blob/main/src/include/mempool.h