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Message-ID: <SJ0PR11MB5678048AA2B4C654E41082D8C9872@SJ0PR11MB5678.namprd11.prod.outlook.com>
Date: Wed, 14 Aug 2024 17:40:50 +0000
From: "Sridhar, Kanchana P" <kanchana.p.sridhar@...el.com>
To: Barry Song <21cnbao@...il.com>
CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-mm@...ck.org" <linux-mm@...ck.org>, "hannes@...xchg.org"
<hannes@...xchg.org>, "yosryahmed@...gle.com" <yosryahmed@...gle.com>,
"nphamcs@...il.com" <nphamcs@...il.com>, "ryan.roberts@....com"
<ryan.roberts@....com>, "Huang, Ying" <ying.huang@...el.com>,
"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>, "Zou, Nanhai"
<nanhai.zou@...el.com>, "Feghali, Wajdi K" <wajdi.k.feghali@...el.com>,
"Gopal, Vinodh" <vinodh.gopal@...el.com>, "Sridhar, Kanchana P"
<kanchana.p.sridhar@...el.com>
Subject: RE: [RFC PATCH v1 2/4] mm: vmstat: Per mTHP-size zswap_store vmstat
event counters.
Hi Barry,
> -----Original Message-----
> From: Barry Song <21cnbao@...il.com>
> Sent: Wednesday, August 14, 2024 12:49 AM
> To: Sridhar, Kanchana P <kanchana.p.sridhar@...el.com>
> Cc: linux-kernel@...r.kernel.org; linux-mm@...ck.org;
> hannes@...xchg.org; yosryahmed@...gle.com; nphamcs@...il.com;
> ryan.roberts@....com; Huang, Ying <ying.huang@...el.com>; akpm@...ux-
> foundation.org; Zou, Nanhai <nanhai.zou@...el.com>; Feghali, Wajdi K
> <wajdi.k.feghali@...el.com>; Gopal, Vinodh <vinodh.gopal@...el.com>
> Subject: Re: [RFC PATCH v1 2/4] mm: vmstat: Per mTHP-size zswap_store
> vmstat event counters.
>
> On Wed, Aug 14, 2024 at 6:28 PM Kanchana P Sridhar
> <kanchana.p.sridhar@...el.com> wrote:
> >
> > Added vmstat event counters per mTHP-size that can be used to account
> > for folios of different sizes being successfully stored in ZSWAP.
> >
> > For this RFC, it is not clear if these zswpout counters should instead
> > be added as part of the existing mTHP stats in
> > /sys/kernel/mm/transparent_hugepage/hugepages-*kB/stats.
> >
> > The following is also a viable option, should it make better sense,
> > for instance, as:
> >
> > /sys/kernel/mm/transparent_hugepage/hugepages-*kB/stats/zswpout.
> >
> > If so, we would be able to distinguish between mTHP zswap and
> > non-zswap swapouts through:
> >
> > /sys/kernel/mm/transparent_hugepage/hugepages-*kB/stats/zswpout
> >
> > and
> >
> > /sys/kernel/mm/transparent_hugepage/hugepages-*kB/stats/swpout
> >
> > respectively.
> >
> > Comments would be appreciated as to which approach is preferable.
>
> Even though swapout might go through zswap, from the perspective of
> the mm core, it shouldn't be aware of that. Shouldn't zswpout be part
> of swpout? Why are they separate? no matter if a mTHP has been
> put in zswap, it has been swapped-out to mm-core? No?
Thanks for the code review comments. This is a good point. I was keeping in
mind the convention used by existing vmstat event counters that distinguish
zswpout/zswpin from pswpout/pswpin events.
If we want to keep the distinction in mTHP swapouts, would adding a
separate MTHP_STAT_ZSWPOUT to "enum mthp_stat_item" be Ok?
In any case, it looks like all that would be needed is a call to
count_mthp_stat(folio_order(folio), MTHP_STAT_[Z]SWPOUT) in the
general case.
I will make this change in v2, depending on whether or not the
separation of zswpout vs. non-zswap swpout is recommended for
mTHP.
>
>
> >
> > Signed-off-by: Kanchana P Sridhar <kanchana.p.sridhar@...el.com>
> > ---
> > include/linux/vm_event_item.h | 15 +++++++++++++++
> > mm/vmstat.c | 15 +++++++++++++++
> > 2 files changed, 30 insertions(+)
> >
> > diff --git a/include/linux/vm_event_item.h
> b/include/linux/vm_event_item.h
> > index 747943bc8cc2..2451bcfcf05c 100644
> > --- a/include/linux/vm_event_item.h
> > +++ b/include/linux/vm_event_item.h
> > @@ -114,6 +114,9 @@ enum vm_event_item { PGPGIN, PGPGOUT,
> PSWPIN, PSWPOUT,
> > THP_ZERO_PAGE_ALLOC,
> > THP_ZERO_PAGE_ALLOC_FAILED,
> > THP_SWPOUT,
> > +#ifdef CONFIG_ZSWAP
> > + ZSWPOUT_PMD_THP_FOLIO,
> > +#endif
> > THP_SWPOUT_FALLBACK,
> > #endif
> > #ifdef CONFIG_MEMORY_BALLOON
> > @@ -143,6 +146,18 @@ enum vm_event_item { PGPGIN, PGPGOUT,
> PSWPIN, PSWPOUT,
> > ZSWPIN,
> > ZSWPOUT,
> > ZSWPWB,
> > + ZSWPOUT_4KB_FOLIO,
> > +#ifdef CONFIG_THP_SWAP
> > + mTHP_ZSWPOUT_8kB,
> > + mTHP_ZSWPOUT_16kB,
> > + mTHP_ZSWPOUT_32kB,
> > + mTHP_ZSWPOUT_64kB,
> > + mTHP_ZSWPOUT_128kB,
> > + mTHP_ZSWPOUT_256kB,
> > + mTHP_ZSWPOUT_512kB,
> > + mTHP_ZSWPOUT_1024kB,
> > + mTHP_ZSWPOUT_2048kB,
> > +#endif
>
> This implementation hardcodes assumptions about the page size being 4KB,
> but page sizes can vary, and so can the THP orders?
Agreed, will address in v2.
>
> > #endif
> > #ifdef CONFIG_X86
> > DIRECT_MAP_LEVEL2_SPLIT,
> > diff --git a/mm/vmstat.c b/mm/vmstat.c
> > index 8507c497218b..0e66c8b0c486 100644
> > --- a/mm/vmstat.c
> > +++ b/mm/vmstat.c
> > @@ -1375,6 +1375,9 @@ const char * const vmstat_text[] = {
> > "thp_zero_page_alloc",
> > "thp_zero_page_alloc_failed",
> > "thp_swpout",
> > +#ifdef CONFIG_ZSWAP
> > + "zswpout_pmd_thp_folio",
> > +#endif
> > "thp_swpout_fallback",
> > #endif
> > #ifdef CONFIG_MEMORY_BALLOON
> > @@ -1405,6 +1408,18 @@ const char * const vmstat_text[] = {
> > "zswpin",
> > "zswpout",
> > "zswpwb",
> > + "zswpout_4kb_folio",
> > +#ifdef CONFIG_THP_SWAP
> > + "mthp_zswpout_8kb",
> > + "mthp_zswpout_16kb",
> > + "mthp_zswpout_32kb",
> > + "mthp_zswpout_64kb",
> > + "mthp_zswpout_128kb",
> > + "mthp_zswpout_256kb",
> > + "mthp_zswpout_512kb",
> > + "mthp_zswpout_1024kb",
> > + "mthp_zswpout_2048kb",
> > +#endif
>
> The issue here is that the number of THP orders
> can vary across different platforms.
Agreed, will address in v2.
Thanks,
Kanchana
>
> > #endif
> > #ifdef CONFIG_X86
> > "direct_map_level2_splits",
> > --
> > 2.27.0
> >
>
> Thanks
> Barry
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