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Date: Thu, 26 Nov 2020 13:31:17 +0100
From: SeongJae Park <sjpark@...zon.com>
To: Shakeel Butt <shakeelb@...gle.com>
CC: SeongJae Park <sjpark@...zon.com>,
SeongJae Park <sjpark@...zon.de>,
<Jonathan.Cameron@...wei.com>,
Andrea Arcangeli <aarcange@...hat.com>, <acme@...nel.org>,
<alexander.shishkin@...ux.intel.com>, <amit@...nel.org>,
<benh@...nel.crashing.org>, <brendan.d.gregg@...il.com>,
Brendan Higgins <brendanhiggins@...gle.com>,
Qian Cai <cai@....pw>,
Colin Ian King <colin.king@...onical.com>,
Jonathan Corbet <corbet@....net>,
"David Hildenbrand" <david@...hat.com>, <dwmw@...zon.com>,
Marco Elver <elver@...gle.com>, "Du, Fan" <fan.du@...el.com>,
<foersleo@...zon.de>, "Greg Thelen" <gthelen@...gle.com>,
Ian Rogers <irogers@...gle.com>, <jolsa@...hat.com>,
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Mel Gorman <mgorman@...e.de>, Minchan Kim <minchan@...nel.org>,
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Subject: Re: [PATCH v22 05/18] mm/idle_page_tracking: Make PG_(idle|young) reusable
On Wed, 25 Nov 2020 07:30:06 -0800 Shakeel Butt <shakeelb@...gle.com> wrote:
> On Tue, Oct 20, 2020 at 2:04 AM SeongJae Park <sjpark@...zon.com> wrote:
> >
> > From: SeongJae Park <sjpark@...zon.de>
> >
> > PG_idle and PG_young allows the two PTE Accessed bit users,
> > IDLE_PAGE_TRACKING and the reclaim logic concurrently work while don't
> > interfere each other. That is, when they need to clear the Accessed
> > bit, they set PG_young
>
> Only PG_young bit
Oops, right. Maybe I was out of my mind while writing this. Thank you for
correcting this.
>
> > and PG_idle to represent the previous state of
> > the bit, respectively. And when they need to read the bit, if the bit
> > is cleared, they further read the PG_young
>
> Again only PG_young bit.
Sure.
>
> PG_idle bit is only read (and set) by the page idle tracking code and
> it can be cleared by others (reclaim or file access).
>
> > and PG_idle, respectively, to
> > know whether the other has cleared the bit meanwhile or not.
> >
> > We could add another page flag and extend the mechanism to use the flag
> > if we need to add another concurrent PTE Accessed bit user subsystem.
> > However, it would be only waste the space. Instead, if the new
> > subsystem is mutually exclusive with IDLE_PAGE_TRACKING, it could simply
> > reuse the PG_idle flag. However, it's impossible because the flags are
> > dependent on IDLE_PAGE_TRACKING.
> >
> > To allow such reuse of the flags, this commit separates the PG_young and
> > PG_idle flag logic from IDLE_PAGE_TRACKING and introduces new kernel
> > config, 'PAGE_IDLE_FLAG'. Hence, if !IDLE_PAGE_TRACKING and
> > IDLE_PAGE_FLAG, a new subsystem would be able to reuse PG_idle.
> >
> > In the next commit, DAMON's reference implementation of the virtual
> > memory address space monitoring primitives will use it.
> >
> > Signed-off-by: SeongJae Park <sjpark@...zon.de>
> > ---
> > include/linux/page-flags.h | 4 ++--
> > include/linux/page_ext.h | 2 +-
> > include/linux/page_idle.h | 6 +++---
> > include/trace/events/mmflags.h | 2 +-
> > mm/Kconfig | 8 ++++++++
> > mm/page_ext.c | 12 +++++++++++-
> > mm/page_idle.c | 10 ----------
> > 7 files changed, 26 insertions(+), 18 deletions(-)
> >
> > diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> > index 6be1aa559b1e..7736d290bb61 100644
> > --- a/include/linux/page-flags.h
> > +++ b/include/linux/page-flags.h
> > @@ -132,7 +132,7 @@ enum pageflags {
> > #ifdef CONFIG_MEMORY_FAILURE
> > PG_hwpoison, /* hardware poisoned page. Don't touch */
> > #endif
> > -#if defined(CONFIG_IDLE_PAGE_TRACKING) && defined(CONFIG_64BIT)
> > +#if defined(CONFIG_PAGE_IDLE_FLAG) && defined(CONFIG_64BIT)
> > PG_young,
> > PG_idle,
> > #endif
> > @@ -432,7 +432,7 @@ static inline bool set_hwpoison_free_buddy_page(struct page *page)
> > #define __PG_HWPOISON 0
> > #endif
> >
> > -#if defined(CONFIG_IDLE_PAGE_TRACKING) && defined(CONFIG_64BIT)
> > +#if defined(CONFIG_PAGE_IDLE_FLAG) && defined(CONFIG_64BIT)
> > TESTPAGEFLAG(Young, young, PF_ANY)
> > SETPAGEFLAG(Young, young, PF_ANY)
> > TESTCLEARFLAG(Young, young, PF_ANY)
> > diff --git a/include/linux/page_ext.h b/include/linux/page_ext.h
> > index cfce186f0c4e..c9cbc9756011 100644
> > --- a/include/linux/page_ext.h
> > +++ b/include/linux/page_ext.h
> > @@ -19,7 +19,7 @@ struct page_ext_operations {
> > enum page_ext_flags {
> > PAGE_EXT_OWNER,
> > PAGE_EXT_OWNER_ALLOCATED,
> > -#if defined(CONFIG_IDLE_PAGE_TRACKING) && !defined(CONFIG_64BIT)
> > +#if defined(CONFIG_PAGE_IDLE_FLAG) && !defined(CONFIG_64BIT)
> > PAGE_EXT_YOUNG,
> > PAGE_EXT_IDLE,
> > #endif
> > diff --git a/include/linux/page_idle.h b/include/linux/page_idle.h
> > index 1e894d34bdce..d8a6aecf99cb 100644
> > --- a/include/linux/page_idle.h
> > +++ b/include/linux/page_idle.h
> > @@ -6,7 +6,7 @@
> > #include <linux/page-flags.h>
> > #include <linux/page_ext.h>
> >
> > -#ifdef CONFIG_IDLE_PAGE_TRACKING
> > +#ifdef CONFIG_PAGE_IDLE_FLAG
> >
> > #ifdef CONFIG_64BIT
> > static inline bool page_is_young(struct page *page)
> > @@ -106,7 +106,7 @@ static inline void clear_page_idle(struct page *page)
> > }
> > #endif /* CONFIG_64BIT */
> >
> > -#else /* !CONFIG_IDLE_PAGE_TRACKING */
> > +#else /* !CONFIG_PAGE_IDLE_FLAG */
> >
> > static inline bool page_is_young(struct page *page)
> > {
> > @@ -135,6 +135,6 @@ static inline void clear_page_idle(struct page *page)
> > {
> > }
> >
> > -#endif /* CONFIG_IDLE_PAGE_TRACKING */
> > +#endif /* CONFIG_PAGE_IDLE_FLAG */
> >
> > #endif /* _LINUX_MM_PAGE_IDLE_H */
> > diff --git a/include/trace/events/mmflags.h b/include/trace/events/mmflags.h
> > index 5fb752034386..4d182c32071b 100644
> > --- a/include/trace/events/mmflags.h
> > +++ b/include/trace/events/mmflags.h
> > @@ -73,7 +73,7 @@
> > #define IF_HAVE_PG_HWPOISON(flag,string)
> > #endif
> >
> > -#if defined(CONFIG_IDLE_PAGE_TRACKING) && defined(CONFIG_64BIT)
> > +#if defined(CONFIG_PAGE_IDLE_FLAG) && defined(CONFIG_64BIT)
> > #define IF_HAVE_PG_IDLE(flag,string) ,{1UL << flag, string}
> > #else
> > #define IF_HAVE_PG_IDLE(flag,string)
> > diff --git a/mm/Kconfig b/mm/Kconfig
> > index 19fe2251c87a..044317ef9143 100644
> > --- a/mm/Kconfig
> > +++ b/mm/Kconfig
> > @@ -761,10 +761,18 @@ config DEFERRED_STRUCT_PAGE_INIT
> > lifetime of the system until these kthreads finish the
> > initialisation.
> >
> > +config PAGE_IDLE_FLAG
> > + bool "Add PG_idle and PG_young flags"
> > + help
> > + This feature adds PG_idle and PG_young flags in 'struct page'. PTE
> > + Accessed bit writers can set the state of the bit in the flags to let
> > + other PTE Accessed bit readers don't disturbed.
> > +
> > config IDLE_PAGE_TRACKING
> > bool "Enable idle page tracking"
> > depends on SYSFS && MMU
> > select PAGE_EXTENSION if !64BIT
> > + select PAGE_IDLE_FLAG
> > help
> > This feature allows to estimate the amount of user pages that have
> > not been touched during a given period of time. This information can
> > diff --git a/mm/page_ext.c b/mm/page_ext.c
> > index a3616f7a0e9e..f9a6ff65ac0a 100644
> > --- a/mm/page_ext.c
> > +++ b/mm/page_ext.c
> > @@ -58,11 +58,21 @@
> > * can utilize this callback to initialize the state of it correctly.
> > */
> >
>
> Is there a need to move the following code in this patch?
After this patchset, someone would turn CONFIG_PAGE_IDLE_FLAG on but
CONFIG_IDLE_PAGE_TRACKING. In that case, the build will fail because
page_idle.c will not be compiled. Because below code is used by page_ext.c
only, I think moving into here is ok.
>
>
> > +#if defined(CONFIG_PAGE_IDLE_FLAG) && !defined(CONFIG_64BIT)
> > +static bool need_page_idle(void)
> > +{
> > + return true;
> > +}
> > +struct page_ext_operations page_idle_ops = {
> > + .need = need_page_idle,
> > +};
> > +#endif
> > +
> > static struct page_ext_operations *page_ext_ops[] = {
> > #ifdef CONFIG_PAGE_OWNER
> > &page_owner_ops,
> > #endif
> > -#if defined(CONFIG_IDLE_PAGE_TRACKING) && !defined(CONFIG_64BIT)
> > +#if defined(CONFIG_PAGE_IDLE_FLAG) && !defined(CONFIG_64BIT)
> > &page_idle_ops,
> > #endif
> > };
> > diff --git a/mm/page_idle.c b/mm/page_idle.c
> > index 057c61df12db..144fb4ed961d 100644
> > --- a/mm/page_idle.c
> > +++ b/mm/page_idle.c
> > @@ -211,16 +211,6 @@ static const struct attribute_group page_idle_attr_group = {
> > .name = "page_idle",
> > };
> >
> > -#ifndef CONFIG_64BIT
> > -static bool need_page_idle(void)
> > -{
> > - return true;
> > -}
> > -struct page_ext_operations page_idle_ops = {
> > - .need = need_page_idle,
> > -};
> > -#endif
> > -
> > static int __init page_idle_init(void)
> > {
> > int err;
> > --
> > 2.17.1
> >
>
> Overall this patch looks good to me.
Appreciate!
Thanks,
SeongJae Park
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