0b9b241406
On a few of our systems, I found frequent 'unshare(CLONE_NEWNET)' calls make the number of active slab objects including 'sock_inode_cache' type rapidly and continuously increase. As a result, memory pressure occurs. In more detail, I made an artificial reproducer that resembles the workload that we found the problem and reproduce the problem faster. It merely repeats 'unshare(CLONE_NEWNET)' 50,000 times in a loop. It takes about 2 minutes. On 40 CPU cores / 70GB DRAM machine, the available memory continuously reduced in a fast speed (about 120MB per second, 15GB in total within the 2 minutes). Note that the issue don't reproduce on every machine. On my 6 CPU cores machine, the problem didn't reproduce. 'cleanup_net()' and 'fqdir_work_fn()' are functions that deallocate the relevant memory objects. They are asynchronously invoked by the work queues and internally use 'rcu_barrier()' to ensure safe destructions. 'cleanup_net()' works in a batched maneer in a single thread worker, while 'fqdir_work_fn()' works for each 'fqdir_exit()' call in the 'system_wq'. Therefore, 'fqdir_work_fn()' called frequently under the workload and made the contention for 'rcu_barrier()' high. In more detail, the global mutex, 'rcu_state.barrier_mutex' became the bottleneck. This commit avoids such contention by doing the 'rcu_barrier()' and subsequent lightweight works in a batched manner, as similar to that of 'cleanup_net()'. The fqdir hashtable destruction, which is done before the 'rcu_barrier()', is still allowed to run in parallel for fast processing, but this commit makes it to use a dedicated work queue instead of the 'system_wq', to make sure that the number of threads is bounded. Signed-off-by: SeongJae Park <sjpark@amazon.de> Reviewed-by: Eric Dumazet <edumazet@google.com> Link: https://lore.kernel.org/r/20201211112405.31158-1-sjpark@amazon.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> |
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| arch | ||
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| drivers | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
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| samples | ||
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| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
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| README | ||
README
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 Restructured Text 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.