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Although the oom_reaper is delayed and it gives the oom victim chance to clean up its address space this might take a while especially for processes with a large address space footprint. In those cases oom_reaper might start racing with the dying task and compete for shared resources - e.g. page table lock contention has been observed. Reduce those races by reaping the oom victim from the other end of the address space. It is also a significant improvement for process_mrelease(). When a process is killed, process_mrelease is used to reap the killed process and often runs concurrently with the dying task. The test data shows that after applying the patch, lock contention is greatly reduced during the procedure of reaping the killed process. The test is conducted on arm64. The following basic perf numbers show that applying this patch significantly reduces pte spin lock contention. Without the patch: |--99.57%-- oom_reaper | |--73.58%-- unmap_page_range | | |--8.67%-- [hit in function] | | |--41.59%-- __pte_offset_map_lock | | |--29.47%-- folio_remove_rmap_ptes | | |--16.11%-- tlb_flush_mmu | |--19.94%-- tlb_finish_mmu | |--3.21%-- folio_remove_rmap_ptes With the patch: |--99.53%-- oom_reaper | |--55.77%-- unmap_page_range | | |--20.49%-- [hit in function] | | |--58.30%-- folio_remove_rmap_ptes | | |--11.48%-- tlb_flush_mmu | | |--3.33%-- folio_mark_accessed | |--32.21%-- tlb_finish_mmu | |--6.93%-- folio_remove_rmap_ptes | |--0.69%-- __pte_offset_map_lock Detailed breakdowns for both scenarios are provided below. The cumulative time for oom_reaper plus exit_mmap(victim) in both cases is also summarized, making the performance improvements clear. +----------------------------------------------------------------+ | Category | Applying patch | Without patch | +-------------------------------+----------------+---------------+ | Total running time | 132.6 | 167.1 | | (exit_mmap + reaper work) | 72.4 + 60.2 | 90.7 + 76.4 | +-------------------------------+----------------+---------------+ | Time waiting for pte spinlock | 1.0 | 33.1 | | (exit_mmap + reaper work) | 0.4 + 0.6 | 10.0 + 23.1 | +-------------------------------+----------------+---------------+ | folio_remove_rmap_ptes time | 42.0 | 41.3 | | (exit_mmap + reaper work) | 18.4 + 23.6 | 22.4 + 18.9 | +----------------------------------------------------------------+ From this report, we can see that: 1. The reduction in total time comes mainly from the decrease in time spent on pte spinlock and other locks. 2. oom_reaper performs more work in some areas, but at the same time, exit_mmap also handles certain tasks more efficiently, such as folio_remove_rmap_ptes. Here is a more detailed perf report. [1] Link: https://lkml.kernel.org/r/20250915162946.5515-3-zhongjinji@honor.com Link: https://lore.kernel.org/all/20250915162619.5133-1-zhongjinji@honor.com/ [1] Signed-off-by: zhongjinji <zhongjinji@honor.com> Reviewed-by: Liam R. Howlett <Liam.Howlett@oracle.com> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Reviewed-by: Suren Baghdasaryan <surenb@google.com> Acked-by: Shakeel Butt <shakeel.butt@linux.dev> Acked-by: Michal Hocko <mhocko@suse.com> Cc: David Rientjes <rientjes@google.com> Cc: Len Brown <lenb@kernel.org> Cc: Thomas Gleinxer <tglx@linutronix.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
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| certs | ||
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| Documentation | ||
| drivers | ||
| fs | ||
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| init | ||
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| ipc | ||
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| lib | ||
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| .editorconfig | ||
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| .gitignore | ||
| .mailmap | ||
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| 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 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.