Re: [PATCH v2] mm: shmem: Rename mTHP shmem counters

[Zi Yan <ziy@nvidia.com>]

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On 10 Jul 2024, at 5:55, Ryan Roberts wrote:

> The legacy PMD-sized THP counters at /proc/vmstat include
> thp_file_alloc, thp_file_fallback and thp_file_fallback_charge, which
> rather confusingly refer to shmem THP and do not include any other types
> of file pages. This is inconsistent since in most other places in the
> kernel, THP counters are explicitly separated for anon, shmem and file
> flavours. However, we are stuck with it since it constitutes a user ABI.
>
> Recently, commit 66f44583f9b6 ("mm: shmem: add mTHP counters for
> anonymous shmem") added equivalent mTHP stats for shmem, keeping the
> same "file_" prefix in the names. But in future, we may want to add
> extra stats to cover actual file pages, at which point, it would all
> become very confusing.
>
> So let's take the opportunity to rename these new counters "shmem_"
> before the change makes it upstream and the ABI becomes immutable. While
> we are at it, let's improve the documentation for the legacy counters to
> make it clear that they count shmem pages only.
>
> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
> Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
> Reviewed-by: Lance Yang <ioworker0@gmail.com>
> ---
>
> Hi All,
>
> Applies on top of yesterday's mm-unstable (2073cda629a4) and tested with mm
> selftests; no regressions observed.
>
> The backstory here is that I'd like to introduce some counters for regular file
> folio allocations to observe how often large folio allocation succeeds, but
> these shmem counters are named "file" which is going to make things confusing.
> So hoping to solve that before commit 66f44583f9b6 ("mm: shmem: add mTHP
> counters for anonymous shmem") goes upstream (it is currently in mm-stable).
>
> Changes since v1 [1]
> ====================
>   - Updated documentation for existing legacy "file_" counters to make it clear
>     they only count shmem pages.
>
> [1] https://lore.kernel.org/linux-mm/20240708112445.2690631-1-ryan.roberts@arm.com/
>
> Thanks,
> Ryan
>
>  Documentation/admin-guide/mm/transhuge.rst | 29 ++++++++++++----------
>  include/linux/huge_mm.h                    |  6 ++---
>  mm/huge_memory.c                           | 12 ++++-----
>  mm/shmem.c                                 |  8 +++---
>  4 files changed, 29 insertions(+), 26 deletions(-)
>
LGTM. Reviewed-by: Zi Yan <ziy@nvidia.com>

--
Best Regards,
Yan, Zi

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