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Message-ID: <CAGsJ_4zH72FyLq5gJm215oiWrtd6uf40L_F1UO6cFZ4sy7qt0A@mail.gmail.com>
Date: Mon, 8 Jul 2024 23:36:31 +1200
From: Barry Song <baohua@...nel.org>
To: Ryan Roberts <ryan.roberts@....com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, Hugh Dickins <hughd@...gle.com>,
Jonathan Corbet <corbet@....net>, David Hildenbrand <david@...hat.com>,
Baolin Wang <baolin.wang@...ux.alibaba.com>, Lance Yang <ioworker0@...il.com>,
Matthew Wilcox <willy@...radead.org>, Zi Yan <ziy@...dia.com>,
Daniel Gomez <da.gomez@...sung.com>, linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v1] mm: shmem: Rename mTHP shmem counters
On Mon, Jul 8, 2024 at 11:24 PM Ryan Roberts <ryan.roberts@....com> 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.
Personally, I think this approach is much clearer. However, I recall
we discussed this
before [1], and it seems that inconsistency is a concern?
[1] https://lore.kernel.org/linux-mm/05d0096e4ec3e572d1d52d33a31a661321ac1551.1713755580.git.baolin.wang@linux.alibaba.com/
>
> Signed-off-by: Ryan Roberts <ryan.roberts@....com>
> ---
>
> Hi All,
>
> Applies on top of today'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).
>
> Admittedly, this change means the mTHP stat names are not the same as the legacy
> PMD-size THP names, but I think that's a smaller issue than having "file_" mTHP
> stats that only count shmem, then having to introduce "file2_" or "pgcache_"
> stats for the regular file memory, which is even more inconsistent IMHO. I guess
> the alternative is to count both shmem and file in these mTHP stats (that's how
> they were documented anyway) but I think it's better to be able to consider them
> separately like we do for all the other counters.
>
> Thanks,
> Ryan
>
> Documentation/admin-guide/mm/transhuge.rst | 12 ++++++------
> include/linux/huge_mm.h | 6 +++---
> mm/huge_memory.c | 12 ++++++------
> mm/shmem.c | 8 ++++----
> 4 files changed, 19 insertions(+), 19 deletions(-)
>
> diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst
> index 747c811ee8f1..8b891689fc13 100644
> --- a/Documentation/admin-guide/mm/transhuge.rst
> +++ b/Documentation/admin-guide/mm/transhuge.rst
> @@ -496,16 +496,16 @@ swpout_fallback
> Usually because failed to allocate some continuous swap space
> for the huge page.
>
> -file_alloc
> - is incremented every time a file huge page is successfully
> +shmem_alloc
> + is incremented every time a shmem huge page is successfully
> allocated.
>
> -file_fallback
> - is incremented if a file huge page is attempted to be allocated
> +shmem_fallback
> + is incremented if a shmem huge page is attempted to be allocated
> but fails and instead falls back to using small pages.
>
> -file_fallback_charge
> - is incremented if a file huge page cannot be charged and instead
> +shmem_fallback_charge
> + is incremented if a shmem huge page cannot be charged and instead
> falls back to using small pages even though the allocation was
> successful.
>
> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> index acb6ac24a07e..cff002be83eb 100644
> --- a/include/linux/huge_mm.h
> +++ b/include/linux/huge_mm.h
> @@ -269,9 +269,9 @@ enum mthp_stat_item {
> MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE,
> MTHP_STAT_SWPOUT,
> MTHP_STAT_SWPOUT_FALLBACK,
> - MTHP_STAT_FILE_ALLOC,
> - MTHP_STAT_FILE_FALLBACK,
> - MTHP_STAT_FILE_FALLBACK_CHARGE,
> + MTHP_STAT_SHMEM_ALLOC,
> + MTHP_STAT_SHMEM_FALLBACK,
> + MTHP_STAT_SHMEM_FALLBACK_CHARGE,
> MTHP_STAT_SPLIT,
> MTHP_STAT_SPLIT_FAILED,
> MTHP_STAT_SPLIT_DEFERRED,
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 9ec64aa2be94..f9696c94e211 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -568,9 +568,9 @@ DEFINE_MTHP_STAT_ATTR(anon_fault_fallback, MTHP_STAT_ANON_FAULT_FALLBACK);
> DEFINE_MTHP_STAT_ATTR(anon_fault_fallback_charge, MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE);
> DEFINE_MTHP_STAT_ATTR(swpout, MTHP_STAT_SWPOUT);
> DEFINE_MTHP_STAT_ATTR(swpout_fallback, MTHP_STAT_SWPOUT_FALLBACK);
> -DEFINE_MTHP_STAT_ATTR(file_alloc, MTHP_STAT_FILE_ALLOC);
> -DEFINE_MTHP_STAT_ATTR(file_fallback, MTHP_STAT_FILE_FALLBACK);
> -DEFINE_MTHP_STAT_ATTR(file_fallback_charge, MTHP_STAT_FILE_FALLBACK_CHARGE);
> +DEFINE_MTHP_STAT_ATTR(shmem_alloc, MTHP_STAT_SHMEM_ALLOC);
> +DEFINE_MTHP_STAT_ATTR(shmem_fallback, MTHP_STAT_SHMEM_FALLBACK);
> +DEFINE_MTHP_STAT_ATTR(shmem_fallback_charge, MTHP_STAT_SHMEM_FALLBACK_CHARGE);
> DEFINE_MTHP_STAT_ATTR(split, MTHP_STAT_SPLIT);
> DEFINE_MTHP_STAT_ATTR(split_failed, MTHP_STAT_SPLIT_FAILED);
> DEFINE_MTHP_STAT_ATTR(split_deferred, MTHP_STAT_SPLIT_DEFERRED);
> @@ -581,9 +581,9 @@ static struct attribute *stats_attrs[] = {
> &anon_fault_fallback_charge_attr.attr,
> &swpout_attr.attr,
> &swpout_fallback_attr.attr,
> - &file_alloc_attr.attr,
> - &file_fallback_attr.attr,
> - &file_fallback_charge_attr.attr,
> + &shmem_alloc_attr.attr,
> + &shmem_fallback_attr.attr,
> + &shmem_fallback_charge_attr.attr,
> &split_attr.attr,
> &split_failed_attr.attr,
> &split_deferred_attr.attr,
> diff --git a/mm/shmem.c b/mm/shmem.c
> index 921d59c3d669..f24dfbd387ba 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -1777,7 +1777,7 @@ static struct folio *shmem_alloc_and_add_folio(struct vm_fault *vmf,
> if (pages == HPAGE_PMD_NR)
> count_vm_event(THP_FILE_FALLBACK);
> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> - count_mthp_stat(order, MTHP_STAT_FILE_FALLBACK);
> + count_mthp_stat(order, MTHP_STAT_SHMEM_FALLBACK);
> #endif
> order = next_order(&suitable_orders, order);
> }
> @@ -1804,8 +1804,8 @@ static struct folio *shmem_alloc_and_add_folio(struct vm_fault *vmf,
> count_vm_event(THP_FILE_FALLBACK_CHARGE);
> }
> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> - count_mthp_stat(folio_order(folio), MTHP_STAT_FILE_FALLBACK);
> - count_mthp_stat(folio_order(folio), MTHP_STAT_FILE_FALLBACK_CHARGE);
> + count_mthp_stat(folio_order(folio), MTHP_STAT_SHMEM_FALLBACK);
> + count_mthp_stat(folio_order(folio), MTHP_STAT_SHMEM_FALLBACK_CHARGE);
> #endif
> }
> goto unlock;
> @@ -2181,7 +2181,7 @@ static int shmem_get_folio_gfp(struct inode *inode, pgoff_t index,
> if (folio_test_pmd_mappable(folio))
> count_vm_event(THP_FILE_ALLOC);
> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> - count_mthp_stat(folio_order(folio), MTHP_STAT_FILE_ALLOC);
> + count_mthp_stat(folio_order(folio), MTHP_STAT_SHMEM_ALLOC);
> #endif
> goto alloced;
> }
> --
> 2.43.0
>
Thanks
Barry
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