Re: [PATCH -v3 01/10] mm, swap: Make swap cluster size same of THP size on x86_64

From: Huang\, Ying
Date: Thu Sep 08 2016 - 13:23:16 EST


"Kirill A. Shutemov" <kirill@xxxxxxxxxxxxx> writes:

> On Wed, Sep 07, 2016 at 09:46:00AM -0700, Huang, Ying wrote:
>> From: Huang Ying <ying.huang@xxxxxxxxx>
>>
>> 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, 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@xxxxxxxxxx>
>> Cc: Shaohua Li <shli@xxxxxxxxxx>
>> Cc: Minchan Kim <minchan@xxxxxxxxxx>
>> Cc: Rik van Riel <riel@xxxxxxxxxx>
>> Suggested-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
>> Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
>> ---
>> 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 4c39728..421d862 100644
>> --- a/arch/x86/Kconfig
>> +++ b/arch/x86/Kconfig
>> @@ -164,6 +164,7 @@ config X86
>> select HAVE_STACK_VALIDATION if X86_64
>> select ARCH_USES_HIGH_VMA_FLAGS if X86_INTEL_MEMORY_PROTECTION_KEYS
>> select ARCH_HAS_PKEYS if X86_INTEL_MEMORY_PROTECTION_KEYS
>> + select ARCH_USES_THP_SWAP_CLUSTER if X86_64
>>
>> config INSTRUCTION_DECODER
>> def_bool y
>> diff --git a/mm/Kconfig b/mm/Kconfig
>> index be0ee11..2da8128 100644
>> --- a/mm/Kconfig
>> +++ b/mm/Kconfig
>> @@ -503,6 +503,19 @@ 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 8f1b97d..4b78402 100644
>> --- a/mm/swapfile.c
>> +++ b/mm/swapfile.c
>> @@ -196,7 +196,11 @@ static void discard_swap_cluster(struct swap_info_struct *si,
>> }
>> }
>>
>> +#ifdef CONFIG_THP_SWAP_CLUSTER
>> +#define SWAPFILE_CLUSTER (HPAGE_SIZE / PAGE_SIZE)
>
> #define SWAPFILE_CLUSTER HPAGE_PMD_NR

Yes. Will change it.

> Note, HPAGE_SIZE is not nessesary HPAGE_PMD_SIZE. I can imagine an arch
> with multiple huge page sizes where HPAGE_SIZE differs from what is used
> for THP.

Thanks for pointing out that!

Best Regards,
Huang, Ying