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

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Date: Wed,  1 May 2024 09:08:03 -0700
From: SeongJae Park <sj@...nel.org>
To: Lance Yang <ioworker0@...il.com>
Cc: SeongJae Park <sj@...nel.org>,
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Subject: Re: [PATCH v4 0/3] Reclaim lazyfree THP without splitting

Hi Lance,

On Wed,  1 May 2024 12:26:57 +0800 Lance Yang <ioworker0@...il.com> 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@...nel.org>


Thanks,
SJ

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