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[PATCH -mm -v7 1/9] mm, swap: Make swap cluster size same of THP size on x86_64

Started by"Huang, Ying" <ying.huang@intel.com>
First post2017-03-28 07:40 +0200
Last post2017-04-01 05:30 +0200
Articles 7 — 4 participants

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  [PATCH -mm -v7 1/9] mm, swap: Make swap cluster size same of THP size on x86_64 "Huang, Ying" <ying.huang@intel.com> - 2017-03-28 07:40 +0200
    Re: [PATCH -mm -v7 1/9] mm, swap: Make swap cluster size same of THP  size on x86_64 "Kirill A. Shutemov" <kirill@shutemov.name> - 2017-03-29 01:40 +0200
      Re: [PATCH -mm -v7 1/9] mm, swap: Make swap cluster size same of THP size on x86_64 "Huang\, Ying" <ying.huang@intel.com> - 2017-03-29 03:20 +0200
    Re: [PATCH -mm -v7 1/9] mm, swap: Make swap cluster size same of THP  size on x86_64 Johannes Weiner <hannes@cmpxchg.org> - 2017-03-29 19:00 +0200
      Re: [PATCH -mm -v7 1/9] mm, swap: Make swap cluster size same of THP size on x86_64 "Huang\, Ying" <ying.huang@intel.com> - 2017-03-30 02:50 +0200
        Re: [PATCH -mm -v7 1/9] mm, swap: Make swap cluster size same of THP  size on x86_64 Johannes Weiner <hannes@cmpxchg.org> - 2017-03-31 17:00 +0200
          Re: [PATCH -mm -v7 1/9] mm, swap: Make swap cluster size same of THP size on x86_64 "Huang\, Ying" <ying.huang@intel.com> - 2017-04-01 05:30 +0200

#1610307 — [PATCH -mm -v7 1/9] mm, swap: Make swap cluster size same of THP size on x86_64

From"Huang, Ying" <ying.huang@intel.com>
Date2017-03-28 07:40 +0200
Subject[PATCH -mm -v7 1/9] mm, swap: Make swap cluster size same of THP size on x86_64
Message-ID<tpS1j-2ZP-3@gated-at.bofh.it>
From: Huang Ying <ying.huang@intel.com>

In this patch, the size of the swap cluster is changed to that of the
THP (Transparent Huge Page) on x86_64 architecture (512).  This is for
the THP swap support on x86_64.  Where one swap cluster will be used to
hold the contents of each THP swapped out.  And some information of the
swapped out THP (such as compound map count) will be recorded in the
swap_cluster_info data structure.

For other architectures which want THP swap support,
ARCH_USES_THP_SWAP_CLUSTER need to be selected in the Kconfig file for
the architecture.

In effect, this will enlarge swap cluster size by 2 times on x86_64.
Which may make it harder to find a free cluster when the swap space
becomes fragmented.  So that, this may reduce the continuous swap space
allocation and sequential write in theory.  The performance test in 0day
shows no regressions caused by this.

Cc: Hugh Dickins <hughd@google.com>
Cc: Shaohua Li <shli@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Rik van Riel <riel@redhat.com>
Suggested-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
---
 arch/x86/Kconfig |  1 +
 mm/Kconfig       | 13 +++++++++++++
 mm/swapfile.c    |  4 ++++
 3 files changed, 18 insertions(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index abfc31fb0bee..852d13878793 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -178,6 +178,7 @@ config X86
 	select USER_STACKTRACE_SUPPORT
 	select VIRT_TO_BUS
 	select X86_FEATURE_NAMES		if PROC_FS
+	select ARCH_USES_THP_SWAP_CLUSTER	if X86_64
 
 config INSTRUCTION_DECODER
 	def_bool y
diff --git a/mm/Kconfig b/mm/Kconfig
index 9b8fccb969dc..7b708e200c29 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -499,6 +499,19 @@ config FRONTSWAP
 
 	  If unsure, say Y to enable frontswap.
 
+config ARCH_USES_THP_SWAP_CLUSTER
+	bool
+	default n
+
+config THP_SWAP_CLUSTER
+	bool
+	depends on SWAP && TRANSPARENT_HUGEPAGE && ARCH_USES_THP_SWAP_CLUSTER
+	default y
+	help
+	  Use one swap cluster to hold the contents of the THP
+	  (Transparent Huge Page) swapped out.  The size of the swap
+	  cluster will be same as that of THP.
+
 config CMA
 	bool "Contiguous Memory Allocator"
 	depends on HAVE_MEMBLOCK && MMU
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 53b5881ee0d6..abc401f72a0a 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -199,7 +199,11 @@ static void discard_swap_cluster(struct swap_info_struct *si,
 	}
 }
 
+#ifdef CONFIG_THP_SWAP_CLUSTER
+#define SWAPFILE_CLUSTER	HPAGE_PMD_NR
+#else
 #define SWAPFILE_CLUSTER	256
+#endif
 #define LATENCY_LIMIT		256
 
 static inline void cluster_set_flag(struct swap_cluster_info *info,
-- 
2.11.0

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#1611434 — Re: [PATCH -mm -v7 1/9] mm, swap: Make swap cluster size same of THP size on x86_64

From"Kirill A. Shutemov" <kirill@shutemov.name>
Date2017-03-29 01:40 +0200
SubjectRe: [PATCH -mm -v7 1/9] mm, swap: Make swap cluster size same of THP size on x86_64
Message-ID<tq8St-6H1-9@gated-at.bofh.it>
In reply to#1610307
On Tue, Mar 28, 2017 at 01:32:01PM +0800, Huang, Ying wrote:
> From: Huang Ying <ying.huang@intel.com>
> 
> In this patch, the size of the swap cluster is changed to that of the
> THP (Transparent Huge Page) on x86_64 architecture (512).  This is for
> the THP swap support on x86_64.  Where one swap cluster will be used to
> hold the contents of each THP swapped out.  And some information of the
> swapped out THP (such as compound map count) will be recorded in the
> swap_cluster_info data structure.
> 
> For other architectures which want THP swap support,
> ARCH_USES_THP_SWAP_CLUSTER need to be selected in the Kconfig file for
> the architecture.

Intreseting case could be architecture with HPAGE_PMD_NR < 256.
Can current code pack more than one THP per claster.

If not we need to have BUILG_BUG_ON() to catch attempt of such enabling.

-- 
 Kirill A. Shutemov

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#1611469

From"Huang\, Ying" <ying.huang@intel.com>
Date2017-03-29 03:20 +0200
Message-ID<tqarf-7UU-3@gated-at.bofh.it>
In reply to#1611434
"Kirill A. Shutemov" <kirill@shutemov.name> writes:

> On Tue, Mar 28, 2017 at 01:32:01PM +0800, Huang, Ying wrote:
>> From: Huang Ying <ying.huang@intel.com>
>> 
>> In this patch, the size of the swap cluster is changed to that of the
>> THP (Transparent Huge Page) on x86_64 architecture (512).  This is for
>> the THP swap support on x86_64.  Where one swap cluster will be used to
>> hold the contents of each THP swapped out.  And some information of the
>> swapped out THP (such as compound map count) will be recorded in the
>> swap_cluster_info data structure.
>> 
>> For other architectures which want THP swap support,
>> ARCH_USES_THP_SWAP_CLUSTER need to be selected in the Kconfig file for
>> the architecture.
>
> Intreseting case could be architecture with HPAGE_PMD_NR < 256.
> Can current code pack more than one THP per claster.

No.  Only one THP for each swap cluster is supported.  But in current
implementation, if HPAGE_PMD_NR < 256, the swap cluster will be < 256
too.  The size of swap cluster will be exact same as HPAGE_PMD_NR.

Best Regards,
Huang, Ying

> If not we need to have BUILG_BUG_ON() to catch attempt of such enabling.

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#1612153 — Re: [PATCH -mm -v7 1/9] mm, swap: Make swap cluster size same of THP size on x86_64

FromJohannes Weiner <hannes@cmpxchg.org>
Date2017-03-29 19:00 +0200
SubjectRe: [PATCH -mm -v7 1/9] mm, swap: Make swap cluster size same of THP size on x86_64
Message-ID<tqp6W-1bC-25@gated-at.bofh.it>
In reply to#1610307
On Tue, Mar 28, 2017 at 01:32:01PM +0800, Huang, Ying wrote:
> @@ -499,6 +499,19 @@ config FRONTSWAP
>  
>  	  If unsure, say Y to enable frontswap.
>  
> +config ARCH_USES_THP_SWAP_CLUSTER
> +	bool
> +	default n

This is fine.

> +config THP_SWAP_CLUSTER
> +	bool
> +	depends on SWAP && TRANSPARENT_HUGEPAGE && ARCH_USES_THP_SWAP_CLUSTER
> +	default y
> +	help
> +	  Use one swap cluster to hold the contents of the THP
> +	  (Transparent Huge Page) swapped out.  The size of the swap
> +	  cluster will be same as that of THP.

But this is a super weird thing to ask the user. How would they know
what to say, if we don't know? I don't think this should be a config
knob at all. Merge the two config items into a simple

config THP_SWAP_CLUSTER
     bool
     default n

and let the archs with reasonable THP sizes select it.

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#1612475

From"Huang\, Ying" <ying.huang@intel.com>
Date2017-03-30 02:50 +0200
Message-ID<tqwrM-6Aq-25@gated-at.bofh.it>
In reply to#1612153
Johannes Weiner <hannes@cmpxchg.org> writes:

> On Tue, Mar 28, 2017 at 01:32:01PM +0800, Huang, Ying wrote:
>> @@ -499,6 +499,19 @@ config FRONTSWAP
>>  
>>  	  If unsure, say Y to enable frontswap.
>>  
>> +config ARCH_USES_THP_SWAP_CLUSTER
>> +	bool
>> +	default n
>
> This is fine.
>
>> +config THP_SWAP_CLUSTER
>> +	bool
>> +	depends on SWAP && TRANSPARENT_HUGEPAGE && ARCH_USES_THP_SWAP_CLUSTER
>> +	default y
>> +	help
>> +	  Use one swap cluster to hold the contents of the THP
>> +	  (Transparent Huge Page) swapped out.  The size of the swap
>> +	  cluster will be same as that of THP.
>
> But this is a super weird thing to ask the user. How would they know
> what to say, if we don't know? I don't think this should be a config
> knob at all. Merge the two config items into a simple

The user will not see this, because there is no string after "bool" to
let user to select it.  The help here is for document only, so that
architecture developers could know what this is for.

> config THP_SWAP_CLUSTER
>      bool
>      default n
>
> and let the archs with reasonable THP sizes select it.

This will have same effect as the original solution except the document
is removed.

Best Regards,
Huang, Ying

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#1614084 — Re: [PATCH -mm -v7 1/9] mm, swap: Make swap cluster size same of THP size on x86_64

FromJohannes Weiner <hannes@cmpxchg.org>
Date2017-03-31 17:00 +0200
SubjectRe: [PATCH -mm -v7 1/9] mm, swap: Make swap cluster size same of THP size on x86_64
Message-ID<tr6bT-5VY-3@gated-at.bofh.it>
In reply to#1612475
On Thu, Mar 30, 2017 at 08:45:56AM +0800, Huang, Ying wrote:
> Johannes Weiner <hannes@cmpxchg.org> writes:
> 
> > On Tue, Mar 28, 2017 at 01:32:01PM +0800, Huang, Ying wrote:
> >> @@ -499,6 +499,19 @@ config FRONTSWAP
> >>  
> >>  	  If unsure, say Y to enable frontswap.
> >>  
> >> +config ARCH_USES_THP_SWAP_CLUSTER
> >> +	bool
> >> +	default n
> >
> > This is fine.
> >
> >> +config THP_SWAP_CLUSTER
> >> +	bool
> >> +	depends on SWAP && TRANSPARENT_HUGEPAGE && ARCH_USES_THP_SWAP_CLUSTER
> >> +	default y
> >> +	help
> >> +	  Use one swap cluster to hold the contents of the THP
> >> +	  (Transparent Huge Page) swapped out.  The size of the swap
> >> +	  cluster will be same as that of THP.
> >
> > But this is a super weird thing to ask the user. How would they know
> > what to say, if we don't know? I don't think this should be a config
> > knob at all. Merge the two config items into a simple
> 
> The user will not see this, because there is no string after "bool" to
> let user to select it.  The help here is for document only, so that
> architecture developers could know what this is for.

Oh, I missed that. My bad!

> > config THP_SWAP_CLUSTER
> >      bool
> >      default n
> >
> > and let the archs with reasonable THP sizes select it.
> 
> This will have same effect as the original solution except the document
> is removed.

Then I still don't understand why we need two config symbols. Can't
archs select the documented THP_SWAP_CLUSTER directly?

The #ifdef in swapfile.c could check THP && THP_SWAP_CLUSTER.

Am I missing something?

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#1614381

From"Huang\, Ying" <ying.huang@intel.com>
Date2017-04-01 05:30 +0200
Message-ID<trhTH-5sS-1@gated-at.bofh.it>
In reply to#1614084
Johannes Weiner <hannes@cmpxchg.org> writes:

> On Thu, Mar 30, 2017 at 08:45:56AM +0800, Huang, Ying wrote:
>> Johannes Weiner <hannes@cmpxchg.org> writes:
>> 
>> > On Tue, Mar 28, 2017 at 01:32:01PM +0800, Huang, Ying wrote:
>> >> @@ -499,6 +499,19 @@ config FRONTSWAP
>> >>  
>> >>  	  If unsure, say Y to enable frontswap.
>> >>  
>> >> +config ARCH_USES_THP_SWAP_CLUSTER
>> >> +	bool
>> >> +	default n
>> >
>> > This is fine.
>> >
>> >> +config THP_SWAP_CLUSTER
>> >> +	bool
>> >> +	depends on SWAP && TRANSPARENT_HUGEPAGE && ARCH_USES_THP_SWAP_CLUSTER
>> >> +	default y
>> >> +	help
>> >> +	  Use one swap cluster to hold the contents of the THP
>> >> +	  (Transparent Huge Page) swapped out.  The size of the swap
>> >> +	  cluster will be same as that of THP.
>> >
>> > But this is a super weird thing to ask the user. How would they know
>> > what to say, if we don't know? I don't think this should be a config
>> > knob at all. Merge the two config items into a simple
>> 
>> The user will not see this, because there is no string after "bool" to
>> let user to select it.  The help here is for document only, so that
>> architecture developers could know what this is for.
>
> Oh, I missed that. My bad!
>
>> > config THP_SWAP_CLUSTER
>> >      bool
>> >      default n
>> >
>> > and let the archs with reasonable THP sizes select it.
>> 
>> This will have same effect as the original solution except the document
>> is removed.
>
> Then I still don't understand why we need two config symbols. Can't
> archs select the documented THP_SWAP_CLUSTER directly?
>
> The #ifdef in swapfile.c could check THP && THP_SWAP_CLUSTER.
>
> Am I missing something?

I use two config symbols just to save some typing, instead of

#ifdef CONFIG_THP_SWAP_CLUSTER

it will be,

#if defined(CONFIG_TRANSPARENT_HUGEPAGE) && defined(CONFIG_THP_SWAP_CLUSTER)

or

#if defined(CONFIG_SWAP) && defined(CONFIG_TRANSPARENT_HUGEPAGE) && defined(CONFIG_THP_SWAP_CLUSTER)

Best Regards,
Huang, Ying

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