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34c8817455
The kfree_rcu() logic can be improved further by using kfree_bulk() interface along with "basic batching support" introduced earlier. The are at least two advantages of using "bulk" interface: - in case of large number of kfree_rcu() requests kfree_bulk() reduces the per-object overhead caused by calling kfree() per-object. - reduces the number of cache-misses due to "pointer chasing" between objects which can be far spread between each other. This approach defines a new kfree_rcu_bulk_data structure that stores pointers in an array with a specific size. Number of entries in that array depends on PAGE_SIZE making kfree_rcu_bulk_data structure to be exactly one page. Since it deals with "block-chain" technique there is an extra need in dynamic allocation when a new block is required. Memory is allocated with GFP_NOWAIT | __GFP_NOWARN flags, i.e. that allows to skip direct reclaim under low memory condition to prevent stalling and fails silently under high memory pressure. The "emergency path" gets maintained when a system is run out of memory. In that case objects are linked into regular list. The "rcuperf" was run to analyze this change in terms of memory consumption and kfree_bulk() throughput. 1) Testing on the Intel(R) Xeon(R) W-2135 CPU @ 3.70GHz, 12xCPUs with following parameters: kfree_loops=200000 kfree_alloc_num=1000 kfree_rcu_test=1 kfree_vary_obj_size=1 dev.2020.01.10a branch Default / CONFIG_SLAB 53607352517 ns, loops: 200000, batches: 1885, memory footprint: 1248MB 53529637912 ns, loops: 200000, batches: 1921, memory footprint: 1193MB 53570175705 ns, loops: 200000, batches: 1929, memory footprint: 1250MB Patch / CONFIG_SLAB 23981587315 ns, loops: 200000, batches: 810, memory footprint: 1219MB 23879375281 ns, loops: 200000, batches: 822, memory footprint: 1190MB 24086841707 ns, loops: 200000, batches: 794, memory footprint: 1380MB Default / CONFIG_SLUB 51291025022 ns, loops: 200000, batches: 1713, memory footprint: 741MB 51278911477 ns, loops: 200000, batches: 1671, memory footprint: 719MB 51256183045 ns, loops: 200000, batches: 1719, memory footprint: 647MB Patch / CONFIG_SLUB 50709919132 ns, loops: 200000, batches: 1618, memory footprint: 456MB 50736297452 ns, loops: 200000, batches: 1633, memory footprint: 507MB 50660403893 ns, loops: 200000, batches: 1628, memory footprint: 429MB in case of CONFIG_SLAB there is double increase in performance and slightly higher memory usage. As for CONFIG_SLUB, the performance figures are better together with lower memory usage. 2) Testing on the HiKey-960, arm64, 8xCPUs with below parameters: CONFIG_SLAB=y kfree_loops=200000 kfree_alloc_num=1000 kfree_rcu_test=1 102898760401 ns, loops: 200000, batches: 5822, memory footprint: 158MB 89947009882 ns, loops: 200000, batches: 6715, memory footprint: 115MB rcuperf shows approximately ~12% better throughput in case of using "bulk" interface. The "drain logic" or its RCU callback does the work faster that leads to better throughput. Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com> Tested-by: Joel Fernandes (Google) <joel@joelfernandes.org> Signed-off-by: Paul E. McKenney <paulmck@kernel.org> |
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