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Message-ID: <20250904122438.22957-1-zhongjinji@honor.com>
Date: Thu, 4 Sep 2025 20:24:38 +0800
From: zhongjinji <zhongjinji@...or.com>
To: <mhocko@...e.com>
CC: <akpm@...ux-foundation.org>, <feng.han@...or.com>,
<liam.howlett@...cle.com>, <linux-kernel@...r.kernel.org>,
<linux-mm@...ck.org>, <liulu.liu@...or.com>, <lorenzo.stoakes@...cle.com>,
<rientjes@...gle.com>, <shakeel.butt@...ux.dev>, <surenb@...gle.com>,
<tglx@...utronix.de>, <zhongjinji@...or.com>
Subject: Re: [PATCH v7 2/2] mm/oom_kill: The OOM reaper traverses the VMA maple tree in reverse order
> On Wed 03-09-25 17:27:29, zhongjinji wrote:
> > 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.
>
> Thank you this is much better!
>
> > Without the patch:
> > |--99.74%-- oom_reaper
> > | |--76.67%-- unmap_page_range
> > | | |--33.70%-- __pte_offset_map_lock
> > | | | |--98.46%-- _raw_spin_lock
> > | | |--27.61%-- free_swap_and_cache_nr
> > | | |--16.40%-- folio_remove_rmap_ptes
> > | | |--12.25%-- tlb_flush_mmu
> > | |--12.61%-- tlb_finish_mmu
> >
> > With the patch:
> > |--98.84%-- oom_reaper
> > | |--53.45%-- unmap_page_range
> > | | |--24.29%-- [hit in function]
> > | | |--48.06%-- folio_remove_rmap_ptes
> > | | |--17.99%-- tlb_flush_mmu
> > | | |--1.72%-- __pte_offset_map_lock
> > | |--30.43%-- tlb_finish_mmu
>
> Just curious. Do I read this correctly that the overall speedup is
> mostly eaten by contention over tlb_finish_mmu?
Here is a more detailed perf report, which includes the execution times
of some important functions. I believe it will address your concerns.
tlb_flush_mmu and tlb_finish_mmu perform similar tasks; they both mainly
call free_pages_and_swap_cache, and its execution time is related to the
number of anonymous pages being reclaimed.
In previous tests, the pte spinlock contention was so obvious that I
overlooked other issues.
Without the patch
|--99.50%-- oom_reaper
| |--0.50%-- [hit in function]
| |--71.06%-- unmap_page_range
| | |--41.75%-- __pte_offset_map_lock
| | |--23.23%-- folio_remove_rmap_ptes
| | |--20.34%-- tlb_flush_mmu
| | | free_pages_and_swap_cache
| | |--2.23%-- folio_mark_accessed
| | |--1.19%-- free_swap_and_cache_nr
| | |--1.13%-- __tlb_remove_folio_pages
| | |--0.76%-- _raw_spin_lock
| |--16.02%-- tlb_finish_mmu
| | |--26.08%-- [hit in function]
| | |--72.97%-- free_pages_and_swap_cache
| | |--0.67%-- free_pages
| |--2.27%-- folio_remove_rmap_ptes
| |--1.54%-- __tlb_remove_folio_pages
| | |--83.47%-- [hit in function]
| |--0.51%-- __pte_offset_map_lock
Period (ms) Symbol
79.180156 oom_reaper
56.321241 unmap_page_range
23.891714 __pte_offset_map_lock
20.711614 free_pages_and_swap_cache
12.831778 tlb_finish_mmu
11.443282 tlb_flush_mmu
With the patch
|--99.54%-- oom_reaper
| |--0.29%-- [hit in function]
| |--57.91%-- unmap_page_range
| | |--20.42%-- [hit in function]
| | |--53.35%-- folio_remove_rmap_ptes
| | | |--5.85%-- [hit in function]
| | |--10.49%-- __pte_offset_map_lock
| | | |--5.17%-- [hit in function]
| | |--8.40%-- tlb_flush_mmu
| | |--2.35%-- _raw_spin_lock
| | |--1.89%-- folio_mark_accessed
| | |--1.64%-- __tlb_remove_folio_pages
| | | |--57.95%-- [hit in function]
| |--36.34%-- tlb_finish_mmu
| | |--14.70%-- [hit in function]
| | |--84.85%-- free_pages_and_swap_cache
| | | |--2.32%-- [hit in function]
| | |--0.37%-- free_pages
| | --0.08%-- free_unref_page
| |--1.94%-- folio_remove_rmap_ptes
| |--1.68%-- __tlb_remove_folio_pages
| |--0.93%-- __pte_offset_map_lock
| |--0.43%-- folio_mark_accessed
Period (ms) Symbol
49.580521 oom_reaper
28.781660 unmap_page_range
18.105898 tlb_finish_mmu
17.688397 free_pages_and_swap_cache
3.471721 __pte_offset_map_lock
2.412970 tlb_flush_mmu
> > Signed-off-by: zhongjinji <zhongjinji@...or.com>
>
> Anyway, the change on its own makes sense to me
> Acked-by: Michal Hocko <mhocko@...e.com>
>
> Thanks for working on the changelog improvements.
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