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Message-ID: <CAK1f24nGQMKYus9pqywUr6FKh+KyRd-RXsArBgdL1ecOEBsT6w@mail.gmail.com>
Date: Sun, 1 Dec 2024 00:22:32 +0800
From: Lance Yang <ioworker0@...il.com>
To: Wenchao Hao <haowenchao22@...il.com>
Cc: Barry Song <21cnbao@...il.com>, 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 Fri, Nov 29, 2024 at 7:49 PM Wenchao Hao <haowenchao22@...il.com> wrote:
>
> 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.
Thanks for following up.
>
> Should I include a "Reviewed-by" or any other tags?
Seems like there is no RB yet. I think we just tweak the doc as Barry
suggested, resend out the new version, and then wait for the folks to
review it ;)
Thanks,
Lance
>
> 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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