Re: [PATCH v9 2/2] mm/oom_kill: The OOM reaper traverses the VMA maple tree in reverse order

zhongjinji
2025-09-11T04:06:16Z

> On Wed 10-09-25 22:37:26, 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.
> >
> > The test is based on arm64.
> >
> > Without the patch:
> > |--99.57%-- oom_reaper
> > | |--0.28%-- [hit in function]
> > | |--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
> > | | |--1.66%-- folio_mark_accessed
> > | | |--0.74%-- free_swap_and_cache_nr
> > | | |--0.69%-- __tlb_remove_folio_pages
> > | |--19.94%-- tlb_finish_mmu
> > | |--3.21%-- folio_remove_rmap_ptes
> > | |--1.16%-- __tlb_remove_folio_pages
> > | |--1.16%-- folio_mark_accessed
> > | |--0.36%-- __pte_offset_map_lock
> >
> > 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
> > | | |--2.65%-- __tlb_remove_folio_pages
> > | | |--1.37%-- _raw_spin_lock
> > | | |--0.68%-- __mod_lruvec_page_state
> > | | |--0.51%-- __pte_offset_map_lock
> > | |--32.21%-- tlb_finish_mmu
> > | |--6.93%-- folio_remove_rmap_ptes
> > | |--1.90%-- __tlb_remove_folio_pages
> > | |--1.55%-- folio_mark_accessed
> > | |--0.69%-- __pte_offset_map_lock
>
> I do not object to the patch but this profile is not telling much really
> as already pointed out in prior versions as we do not know the base
> those percentages are from. It would be really much more helpful to
> measure the elapse time for the oom_repaer and exit_mmap to see those
> gains.

I got it. I will reference the perf report like this [1] in the changelog.
link : https://lore.kernel.org/all/20250908121503.20960-1-zhongjinji@honor.com/ [1]