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2fba5961c6
Patch series "memcg: decouple memcg and objcg stocks", v3. The per-cpu memcg charge cache and objcg charge cache are coupled in a single struct memcg_stock_pcp and a single local lock is used to protect both of the caches. This makes memcg charging and objcg charging nmi safe challenging. Decoupling memcg and objcg stocks would allow us to make them nmi safe and even work without disabling irqs independently. This series completely decouples memcg and objcg stocks. To evaluate the impact of this series with and without PREEMPT_RT config, we ran varying number of netperf clients in different cgroups on a 72 CPU machine. $ netserver -6 $ netperf -6 -H ::1 -l 60 -t TCP_SENDFILE -- -m 10K PREEMPT_RT config: ------------------ number of clients | Without series | With series 6 | 38559.1 Mbps | 38652.6 Mbps 12 | 37388.8 Mbps | 37560.1 Mbps 18 | 30707.5 Mbps | 31378.3 Mbps 24 | 25908.4 Mbps | 26423.9 Mbps 30 | 22347.7 Mbps | 22326.5 Mbps 36 | 20235.1 Mbps | 20165.0 Mbps !PREEMPT_RT config: ------------------- number of clients | Without series | With series 6 | 50235.7 Mbps | 51415.4 Mbps 12 | 49336.5 Mbps | 49901.4 Mbps 18 | 46306.8 Mbps | 46482.7 Mbps 24 | 38145.7 Mbps | 38729.4 Mbps 30 | 30347.6 Mbps | 31698.2 Mbps 36 | 26976.6 Mbps | 27364.4 Mbps No performance regression was observed. This patch (of 4): consume_stock() does not need to check gfp_mask for spinning and can simply trylock the local lock to decide to proceed or fail. No need to spin at all for local lock. One of the concern raised was that on PREEMPT_RT kernels, this trylock can fail more often due to tasks having lock_lock can be preempted. This can potentially cause the task which have preempted the task having the local_lock to take the slow path of memcg charging. However this behavior will only impact the performance if memcg charging slowpath is worse than two context switches and possibly scheduling delay behavior of current code. From the network intensive workload experiment it does not seem like the case. We ran varying number of netperf clients in different cgroups on a 72 CPU machine for PREEMPT_RT config. $ netserver -6 $ netperf -6 -H ::1 -l 60 -t TCP_SENDFILE -- -m 10K number of clients | Without series | With series 6 | 38559.1 Mbps | 38652.6 Mbps 12 | 37388.8 Mbps | 37560.1 Mbps 18 | 30707.5 Mbps | 31378.3 Mbps 24 | 25908.4 Mbps | 26423.9 Mbps 30 | 22347.7 Mbps | 22326.5 Mbps 36 | 20235.1 Mbps | 20165.0 Mbps We don't see any significant performance difference for the network intensive workload with this series. Link: https://lkml.kernel.org/r/20250506225533.2580386-1-shakeel.butt@linux.dev Link: https://lkml.kernel.org/r/20250506225533.2580386-2-shakeel.butt@linux.dev Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev> Reviewed-by: Vlastimil Babka <vbabka@suse.cz> Cc: Alexei Starovoitov <ast@kernel.org> Cc: Eric Dumaze <edumazet@google.com> Cc: Jakub Kacinski <kuba@kernel.org> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Muchun Song <muchun.song@linux.dev> Cc: Roman Gushchin <roman.gushchin@linux.dev> Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.