Re: [PATCH v4 0/3] Reclaim lazyfree THP without splitting

[Lance Yang]

On Thu, May 2, 2024 at 12:08 AM SeongJae Park <sj@xxxxxxxxxx> wrote:
>
> Hi Lance,
>
> On Wed,  1 May 2024 12:26:57 +0800 Lance Yang <ioworker0@xxxxxxxxx> wrote:
>
> > Hi all,
> >
> > This series adds support for reclaiming PMD-mapped THP marked as lazyfree
> > without needing to first split the large folio via split_huge_pmd_address().
> >
> > When the user no longer requires the pages, they would use madvise(MADV_FREE)
> > to mark the pages as lazy free. Subsequently, they typically would not re-write
> > to that memory again.
> >
> > During memory reclaim, if we detect that the large folio and its PMD are both
> > still marked as clean and there are no unexpected references(such as GUP), so we
> > can just discard the memory lazily, improving the efficiency of memory
> > reclamation in this case.
> >
> > Performance Testing
> > ===================
> >
> > On an Intel i5 CPU, reclaiming 1GiB of lazyfree THPs using
> > mem_cgroup_force_empty() results in the following runtimes in seconds
> > (shorter is better):
> >
> > --------------------------------------------
> > |     Old       |      New       |  Change  |
> > --------------------------------------------
> > |   0.683426    |    0.049197    |  -92.80% |
> > --------------------------------------------
> >
> > ---
> >
> > Changes since v3 [3]
> > ====================
> >  - mm/rmap: integrate PMD-mapped folio splitting into pagewalk loop
> >     - Resolve compilation errors by handling the case where
> >       CONFIG_PGTABLE_HAS_HUGE_LEAVES is undefined (thanks to SeongJae Park)
>
> I confirmed that the issue I reported before is disappeared with this version
> of the patchset.  For the fix,
>
> Tested-by: SeongJae Park <sj@xxxxxxxxxx>

Hey SJ,

Thanks for taking time to confirm! I appreciate your feedback!

Thanks,
Lance

>
>
> Thanks,
> SJ
>
> [...]