e7b9cea718
On our HDFS servers with 12 HDDs per server, a HDFS datanode[0] startup involves scanning all files and caching their metadata (including dentries and inodes) in memory. Each HDD contains approximately 2 million files, resulting in a total of ~20 million cached dentries after initialization. To minimize dentry reclamation, we set vfs_cache_pressure to 1. Despite this configuration, memory pressure conditions can still trigger reclamation of up to 50% of cached dentries, reducing the cache from 20 million to approximately 10 million entries. During the subsequent cache rebuild period, any HDFS datanode restart operation incurs substantial latency penalties until full cache recovery completes. To maintain service stability, we need to preserve more dentries during memory reclamation. The current minimum reclaim ratio (1/100 of total dentries) remains too aggressive for our workload. This patch introduces vfs_cache_pressure_denom for more granular cache pressure control. The configuration [vfs_cache_pressure=1, vfs_cache_pressure_denom=10000] effectively maintains the full 20 million dentry cache under memory pressure, preventing datanode restart performance degradation. Link: https://hadoop.apache.org/docs/r1.2.1/hdfs_design.html#NameNode+and+DataNodes [0] Signed-off-by: Yafang Shao <laoar.shao@gmail.com> Link: https://lore.kernel.org/20250511083624.9305-1-laoar.shao@gmail.com Reviewed-by: Jan Kara <jack@suse.cz> Signed-off-by: Christian Brauner <brauner@kernel.org> |
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| .. | ||
| abi.rst | ||
| fs.rst | ||
| index.rst | ||
| kernel.rst | ||
| net.rst | ||
| sunrpc.rst | ||
| user.rst | ||
| vm.rst | ||