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Message-ID: <6dbd2d37-91ca-4566-af4a-7b4153d2001c@gmail.com>
Date: Fri, 29 Nov 2024 19:49:22 +0800
From: Wenchao Hao <haowenchao22@...il.com>
To: Lance Yang <ioworker0@...il.com>, Barry Song <21cnbao@...il.com>
Cc: Jonathan Corbet <corbet@....net>,
Andrew Morton <akpm@...ux-foundation.org>,
David Hildenbrand <david@...hat.com>, Ryan Roberts <ryan.roberts@....com>,
Baolin Wang <baolin.wang@...ux.alibaba.com>,
Usama Arif <usamaarif642@...il.com>, Matthew Wilcox <willy@...radead.org>,
Peter Xu <peterx@...hat.com>, linux-doc@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v2] mm: add per-order mTHP swap-in
fallback/fallback_charge counters
On 2024/11/24 15:28, Lance Yang wrote:
> On Sun, Nov 24, 2024 at 3:11 PM Barry Song <21cnbao@...il.com> wrote:
>>
>> On Sun, Nov 24, 2024 at 2:56 PM Lance Yang <ioworker0@...il.com> wrote:
>>>
>>> On Sat, Nov 23, 2024 at 9:17 PM Wenchao Hao <haowenchao22@...il.com> wrote:
>>>>
>>>> On 2024/11/23 19:52, Lance Yang wrote:
>>>>> On Sat, Nov 23, 2024 at 6:27 PM Barry Song <21cnbao@...il.com> wrote:
>>>>>>
>>>>>> On Sat, Nov 23, 2024 at 10:36 AM Lance Yang <ioworker0@...il.com> wrote:
>>>>>>>
>>>>>>> Hi Wenchao,
>>>>>>>
>>>>>>> On Sat, Nov 23, 2024 at 12:14 AM Wenchao Hao <haowenchao22@...il.com> wrote:
>>>>>>>>
>>>>>>>> Currently, large folio swap-in is supported, but we lack a method to
>>>>>>>> analyze their success ratio. Similar to anon_fault_fallback, we introduce
>>>>>>>> per-order mTHP swpin_fallback and swpin_fallback_charge counters for
>>>>>>>> calculating their success ratio. The new counters are located at:
>>>>>>>>
>>>>>>>> /sys/kernel/mm/transparent_hugepage/hugepages-<size>/stats/
>>>>>>>> swpin_fallback
>>>>>>>> swpin_fallback_charge
>>>>>>>>
>>>>>>>> Signed-off-by: Wenchao Hao <haowenchao22@...il.com>
>>>>>>>> ---
>>>>>>>> V2:
>>>>>>>> Introduce swapin_fallback_charge, which increments if it fails to
>>>>>>>> charge a huge page to memory despite successful allocation.
>>>>>>>>
>>>>>>>> Documentation/admin-guide/mm/transhuge.rst | 10 ++++++++++
>>>>>>>> include/linux/huge_mm.h | 2 ++
>>>>>>>> mm/huge_memory.c | 6 ++++++
>>>>>>>> mm/memory.c | 2 ++
>>>>>>>> 4 files changed, 20 insertions(+)
>>>>>>>>
>>>>>>>> diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst
>>>>>>>> index 5034915f4e8e..9c07612281b5 100644
>>>>>>>> --- a/Documentation/admin-guide/mm/transhuge.rst
>>>>>>>> +++ b/Documentation/admin-guide/mm/transhuge.rst
>>>>>>>> @@ -561,6 +561,16 @@ swpin
>>>>>>>> is incremented every time a huge page is swapped in from a non-zswap
>>>>>>>> swap device in one piece.
>>>>>>>>
>>>>>>>
>>>>>>> Would the following be better?
>>>>>>>
>>>>>>> +swpin_fallback
>>>>>>> + is incremented if a huge page swapin fails to allocate or charge
>>>>>>> + it and instead falls back to using small pages.
>>>>>>>
>>>>>>> +swpin_fallback_charge
>>>>>>> + is incremented if a huge page swapin fails to charge it and instead
>>>>>>> + falls back to using small pages even though the allocation was
>>>>>>> + successful.
>>>>>>
>>>>>> much better, but it is better to align with "huge pages with
>>>>>> lower orders or small pages", not necessarily small pages:
>>>>>>
>>>>>> anon_fault_fallback
>>>>>> is incremented if a page fault fails to allocate or charge
>>>>>> a huge page and instead falls back to using huge pages with
>>>>>> lower orders or small pages.
>>>>>>
>>>>>> anon_fault_fallback_charge
>>>>>> is incremented if a page fault fails to charge a huge page and
>>>>>> instead falls back to using huge pages with lower orders or
>>>>>> small pages even though the allocation was successful.
>>>>>
>>>>> Right, I clearly overlooked that ;)
>>>>>
>>>>
>>>> Hi Lance and Barry,
>>>>
>>>> Do you think the following expression is clear? Compared to my original
>>>> version, I’ve removed the word “huge” from the first line, and it now
>>>> looks almost identical to anon_fault_fallback/anon_fault_fallback_charge.
>>>
>>> Well, that's fine with me. And let's see Barry's opinion as well ;)
>>
>> I still prefer Lance's version. The fallback path in it only needs to
>> be adjusted to
>> include huge pages with lower orders. In contrast, Wenchao's version feels less
>> natural to me because "page swapin" sounds quite odd - we often hear
>> "page fault,"
>> but we have never encountered "page swapin."
>
> Yeah, it makes sense to me ~
>
>>
>> So I mean:
>>
>> swpin_fallback
>> is incremented if swapin fails to allocate or charge a huge
>> page and instead
>> falls back to using huge pages with lower orders or small pages.
>>
>> swpin_fallback_charge
>> is incremented if swapin fails to charge a huge page and instead
>> falls back to using huge pages with lower orders or small
>> pages even though
>> the allocation was successful.
>
> IHMO, much better and clearer than before ;)
>
Hi,
Thank you both very much for your valuable suggestions. I am only
now able to respond to your emails due to a network issue.
I will make the revisions based on your feedback and send the third
version of the patch.
Should I include a "Reviewed-by" or any other tags?
Thanks again,
Wenchao
> Thank,
> Lance
>
>>
>>>
>>> Thanks,
>>> Lance
>>>
>>>>
>>>> swpin_fallback
>>>> is incremented if a page swapin fails to allocate or charge
>>>> a huge page and instead falls back to using huge pages with
>>>> lower orders or small pages.
>>>>
>>>> swpin_fallback_charge
>>>> is incremented if a page swapin fails to charge a huge page and
>>>> instead falls back to using huge pages with lower orders or
>>>> small pages even though the allocation was successful.
>>>>
>>>> Thanks,
>>>> Wencaho
>>>>
>>>>> Thanks,
>>>>> Lance
>>>>>
>>>>>>
>>>>>>>
>>>>>>> Thanks,
>>>>>>> Lance
>>>>>>>
>>>>>>>> +swpin_fallback
>>>>>>>> + is incremented if a huge page swapin fails to allocate or charge
>>>>>>>> + a huge page and instead falls back to using huge pages with
>>>>>>>> + lower orders or small pages.
>>>>>>>> +
>>>>>>>> +swpin_fallback_charge
>>>>>>>> + is incremented if a page swapin fails to charge a huge page and
>>>>>>>> + instead falls back to using huge pages with lower orders or
>>>>>>>> + small pages even though the allocation was successful.
>>>>>>>> +
>>>>>>>> swpout
>>>>>>>> is incremented every time a huge page is swapped out to a non-zswap
>>>>>>>> swap device in one piece without splitting.
>>>>>>>> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
>>>>>>>> index b94c2e8ee918..93e509b6c00e 100644
>>>>>>>> --- a/include/linux/huge_mm.h
>>>>>>>> +++ b/include/linux/huge_mm.h
>>>>>>>> @@ -121,6 +121,8 @@ enum mthp_stat_item {
>>>>>>>> MTHP_STAT_ANON_FAULT_FALLBACK_CHARGE,
>>>>>>>> MTHP_STAT_ZSWPOUT,
>>>>>>>> MTHP_STAT_SWPIN,
>>>>>>>> + MTHP_STAT_SWPIN_FALLBACK,
>>>>>>>> + MTHP_STAT_SWPIN_FALLBACK_CHARGE,
>>>>>>>> MTHP_STAT_SWPOUT,
>>>>>>>> MTHP_STAT_SWPOUT_FALLBACK,
>>>>>>>> MTHP_STAT_SHMEM_ALLOC,
>>>>>>>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>>>>>>>> index ee335d96fc39..46749dded1c9 100644
>>>>>>>> --- a/mm/huge_memory.c
>>>>>>>> +++ b/mm/huge_memory.c
>>>>>>>> @@ -617,6 +617,8 @@ 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(zswpout, MTHP_STAT_ZSWPOUT);
>>>>>>>> DEFINE_MTHP_STAT_ATTR(swpin, MTHP_STAT_SWPIN);
>>>>>>>> +DEFINE_MTHP_STAT_ATTR(swpin_fallback, MTHP_STAT_SWPIN_FALLBACK);
>>>>>>>> +DEFINE_MTHP_STAT_ATTR(swpin_fallback_charge, MTHP_STAT_SWPIN_FALLBACK_CHARGE);
>>>>>>>> DEFINE_MTHP_STAT_ATTR(swpout, MTHP_STAT_SWPOUT);
>>>>>>>> DEFINE_MTHP_STAT_ATTR(swpout_fallback, MTHP_STAT_SWPOUT_FALLBACK);
>>>>>>>> #ifdef CONFIG_SHMEM
>>>>>>>> @@ -637,6 +639,8 @@ static struct attribute *anon_stats_attrs[] = {
>>>>>>>> #ifndef CONFIG_SHMEM
>>>>>>>> &zswpout_attr.attr,
>>>>>>>> &swpin_attr.attr,
>>>>>>>> + &swpin_fallback_attr.attr,
>>>>>>>> + &swpin_fallback_charge_attr.attr,
>>>>>>>> &swpout_attr.attr,
>>>>>>>> &swpout_fallback_attr.attr,
>>>>>>>> #endif
>>>>>>>> @@ -669,6 +673,8 @@ static struct attribute *any_stats_attrs[] = {
>>>>>>>> #ifdef CONFIG_SHMEM
>>>>>>>> &zswpout_attr.attr,
>>>>>>>> &swpin_attr.attr,
>>>>>>>> + &swpin_fallback_attr.attr,
>>>>>>>> + &swpin_fallback_charge_attr.attr,
>>>>>>>> &swpout_attr.attr,
>>>>>>>> &swpout_fallback_attr.attr,
>>>>>>>> #endif
>>>>>>>> diff --git a/mm/memory.c b/mm/memory.c
>>>>>>>> index 209885a4134f..774dfd309cfe 100644
>>>>>>>> --- a/mm/memory.c
>>>>>>>> +++ b/mm/memory.c
>>>>>>>> @@ -4189,8 +4189,10 @@ static struct folio *alloc_swap_folio(struct vm_fault *vmf)
>>>>>>>> if (!mem_cgroup_swapin_charge_folio(folio, vma->vm_mm,
>>>>>>>> gfp, entry))
>>>>>>>> return folio;
>>>>>>>> + count_mthp_stat(order, MTHP_STAT_SWPIN_FALLBACK_CHARGE);
>>>>>>>> folio_put(folio);
>>>>>>>> }
>>>>>>>> + count_mthp_stat(order, MTHP_STAT_SWPIN_FALLBACK);
>>>>>>>> order = next_order(&orders, order);
>>>>>>>> }
>>>>>>>>
>>>>>>>> --
>>>>>>>> 2.45.0
>>>>>>>>
>>>>>>
>>
>> Thanks
>> Barry
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