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  1. Lustre
  2. LU-13312

Optimized RA for stride read under memory pressure

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Details

    • Improvement
    • Resolution: Fixed
    • Minor
    • Lustre 2.14.0
    • None
    • master
    • 9223372036854775807

    Description

      LU-12518 introduced new RA and it supports for page unaligned stride IO and significant improved performance (e.g. IO500 IOR_hard_read). However, it still can be optimized. The current patch sometimes doesn't work well under memory pressure?, but performance is back after dropping page caches before read. Here is a reproducer and results.

      4 x client(1 x Gold 5218, 96GB RAM)
      segment=400000 (~300GB per node)

      # mpirun -np 64 ior -w -s 400000 -a POSIX -i 1 -C -Q 1 -g -G 27 -k -e -t 47008 -b 47008 -o /fast/dir/file -O stoneWallingStatusFile=/fast/dir/stonewall -O stoneWallingWearOut=1 -D 300
      
      # mpirun -np 64 ior -r -s 400000 -a POSIX -i 1 -C -Q 1 -g -G 27 -k -e -t 47008 -b 47008 -o /fast/dir/file -O stoneWallingStatusFile=/fast/dir/stonewall -O stoneWallingWearOut=1 -D 300
       
      Max Read:  5087.32 MiB/sec (5334.44 MB/sec)
      
      One of client's RA stat
      # lctl get_param llite.*.read_ahead_stats
      llite.fast-ffff99878133d000.read_ahead_stats=
      snapshot_time             1582946538.113259755 secs.nsecs
      hits                      72125088 samples [pages]
      misses                    1686810 samples [pages]
      readpage not consecutive  6400000 samples [pages]
      miss inside window        3011 samples [pages]
      failed grab_cache_page    2945424 samples [pages]
      read but discarded        35565 samples [pages]
      zero size window          100245 samples [pages]
      failed to reach end       73663094 samples [pages]
      failed to fast read       6396933 samples [pages]
      

      After dropping pagecache on clients before read.

      # clush -a "echo 3 > /proc/sys/vm/drop_caches "
      # mpirun -np 64 ior -r -s 400000 -a POSIX -i 1 -C -Q 1 -g -G 27 -k -e -t 47008 -b 47008 -o /fast/dir/file -O stoneWallingStatusFile=/fast/dir/stonewall -O stoneWallingWearOut=1 -D 300
      
      Max Read:  16244.62 MiB/sec (17033.72 MB/sec)
      
      Client's RA stat
      # lctl get_param llite.*.read_ahead_stats
      llite.fast-ffff99878133d000.read_ahead_stats=
      snapshot_time             1582947544.040550353 secs.nsecs
      hits                      73799940 samples [pages]
      misses                    63 samples [pages]
      readpage not consecutive  6400000 samples [pages]
      failed grab_cache_page    2654231 samples [pages]
      read but discarded        1 samples [pages]
      zero size window          500 samples [pages]
      failed to reach end       402367 samples [pages]
      failed to fast read       35075 samples [pages]
      

       

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            wshilong Wang Shilong (Inactive)
            sihara Shuichi Ihara
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              Created:
              Updated:
              Resolved: