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 oRN/L0od 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 27/11/2025 11:38, Jon Hunter wrote: > > > On 31/10/2025 21:32, Daniel Gomez wrote: >> >> >> On 10/09/2025 10.01, Vlastimil Babka wrote: >>> Extend the sheaf infrastructure for more efficient kfree_rcu() handling. >>> For caches with sheaves, on each cpu maintain a rcu_free sheaf in >>> addition to main and spare sheaves. >>> >>> kfree_rcu() operations will try to put objects on this sheaf. Once full, >>> the sheaf is detached and submitted to call_rcu() with a handler that >>> will try to put it in the barn, or flush to slab pages using bulk free, >>> when the barn is full. Then a new empty sheaf must be obtained to put >>> more objects there. >>> >>> It's possible that no free sheaves are available to use for a new >>> rcu_free sheaf, and the allocation in kfree_rcu() context can only use >>> GFP_NOWAIT and thus may fail. In that case, fall back to the existing >>> kfree_rcu() implementation. >>> >>> Expected advantages: >>> - batching the kfree_rcu() operations, that could eventually replace the >>>    existing batching >>> - sheaves can be reused for allocations via barn instead of being >>>    flushed to slabs, which is more efficient >>>    - this includes cases where only some cpus are allowed to process rcu >>>      callbacks (Android) >>> >>> Possible disadvantage: >>> - objects might be waiting for more than their grace period (it is >>>    determined by the last object freed into the sheaf), increasing >>> memory >>>    usage - but the existing batching does that too. >>> >>> Only implement this for CONFIG_KVFREE_RCU_BATCHED as the tiny >>> implementation favors smaller memory footprint over performance. >>> >>> Also for now skip the usage of rcu sheaf for CONFIG_PREEMPT_RT as the >>> contexts where kfree_rcu() is called might not be compatible with taking >>> a barn spinlock or a GFP_NOWAIT allocation of a new sheaf taking a >>> spinlock - the current kfree_rcu() implementation avoids doing that. >>> >>> Teach kvfree_rcu_barrier() to flush all rcu_free sheaves from all caches >>> that have them. This is not a cheap operation, but the barrier usage is >>> rare - currently kmem_cache_destroy() or on module unload. >>> >>> Add CONFIG_SLUB_STATS counters free_rcu_sheaf and free_rcu_sheaf_fail to >>> count how many kfree_rcu() used the rcu_free sheaf successfully and how >>> many had to fall back to the existing implementation. >>> >>> Signed-off-by: Vlastimil Babka >> >> Hi Vlastimil, >> >> This patch increases kmod selftest (stress module loader) runtime by >> about >> ~50-60%, from ~200s to ~300s total execution time. My tested kernel has >> CONFIG_KVFREE_RCU_BATCHED enabled. Any idea or suggestions on what >> might be >> causing this, or how to address it? >> > > I have been looking into a regression for Linux v6.18-rc where time > taken to run some internal graphics tests on our Tegra234 device has > increased from around 35% causing the tests to timeout. Bisect is I meant 'increased by around 35%'. > pointing to this commit and I also see we have CONFIG_KVFREE_RCU_BATCHED=y. > > I have not tried disabling CONFIG_KVFREE_RCU_BATCHED=y but I can. I am > not sure if there are any downsides to disabling this? > > Thanks > Jon > -- nvpublic