Re: [PATCH 03/23] thp: compile-time and sysfs knob for thp pagecache

[Ning Qu <quning@google.com>]

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One minor question inline.

Best wishes,
-- 
Ning Qu (曲宁) | Software Engineer | quning@google.com | +1-408-418-6066


On Sat, Aug 3, 2013 at 7:17 PM, Kirill A. Shutemov <
kirill.shutemov@linux.intel.com> wrote:

> From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
>
> For now, TRANSPARENT_HUGEPAGE_PAGECACHE is only implemented for x86_64.
>
> Radix tree perload overhead can be significant on BASE_SMALL systems, so
> let's add dependency on !BASE_SMALL.
>
> /sys/kernel/mm/transparent_hugepage/page_cache is runtime knob for the
> feature. It's enabled by default if TRANSPARENT_HUGEPAGE_PAGECACHE is
> enabled.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> ---
>  Documentation/vm/transhuge.txt |  9 +++++++++
>  include/linux/huge_mm.h        |  9 +++++++++
>  mm/Kconfig                     | 12 ++++++++++++
>  mm/huge_memory.c               | 23 +++++++++++++++++++++++
>  4 files changed, 53 insertions(+)
>
> diff --git a/Documentation/vm/transhuge.txt
> b/Documentation/vm/transhuge.txt
> index 4a63953..4cc15c4 100644
> --- a/Documentation/vm/transhuge.txt
> +++ b/Documentation/vm/transhuge.txt
> @@ -103,6 +103,15 @@ echo always
> >/sys/kernel/mm/transparent_hugepage/enabled
>  echo madvise >/sys/kernel/mm/transparent_hugepage/enabled
>  echo never >/sys/kernel/mm/transparent_hugepage/enabled
>
> +If TRANSPARENT_HUGEPAGE_PAGECACHE is enabled kernel will use huge pages in
> +page cache if possible. It can be disable and re-enabled via sysfs:
> +
> +echo 0 >/sys/kernel/mm/transparent_hugepage/page_cache
> +echo 1 >/sys/kernel/mm/transparent_hugepage/page_cache
> +
> +If it's disabled kernel will not add new huge pages to page cache and
> +split them on mapping, but already mapped pages will stay intakt.
> +
>  It's also possible to limit defrag efforts in the VM to generate
>  hugepages in case they're not immediately free to madvise regions or
>  to never try to defrag memory and simply fallback to regular pages
> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> index 3935428..1534e1e 100644
> --- a/include/linux/huge_mm.h
> +++ b/include/linux/huge_mm.h
> @@ -40,6 +40,7 @@ enum transparent_hugepage_flag {
>         TRANSPARENT_HUGEPAGE_DEFRAG_FLAG,
>         TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG,
>         TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG,
> +       TRANSPARENT_HUGEPAGE_PAGECACHE,
>         TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG,
>  #ifdef CONFIG_DEBUG_VM
>         TRANSPARENT_HUGEPAGE_DEBUG_COW_FLAG,
> @@ -229,4 +230,12 @@ static inline int do_huge_pmd_numa_page(struct
> mm_struct *mm, struct vm_area_str
>
>  #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
>
> +static inline bool transparent_hugepage_pagecache(void)
> +{
> +       if (!IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE_PAGECACHE))
> +               return false;
> +       if (!(transparent_hugepage_flags & (1<<TRANSPARENT_HUGEPAGE_FLAG)))
>

Here, I suppose we should test the  TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG as
well? E.g.
        if (!(transparent_hugepage_flags &
              ((1<<TRANSPARENT_HUGEPAGE_FLAG) |
               (1<<TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG))))

+               return false;
> +       return transparent_hugepage_flags &
> (1<<TRANSPARENT_HUGEPAGE_PAGECACHE);
> +}
>  #endif /* _LINUX_HUGE_MM_H */
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 256bfd0..1e30ee8 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -420,6 +420,18 @@ choice
>           benefit.
>  endchoice
>
> +config TRANSPARENT_HUGEPAGE_PAGECACHE
> +       bool "Transparent Hugepage Support for page cache"
> +       depends on X86_64 && TRANSPARENT_HUGEPAGE
> +       # avoid radix tree preload overhead
> +       depends on !BASE_SMALL
> +       default y
> +       help
> +         Enabling the option adds support hugepages for file-backed
> +         mappings. It requires transparent hugepage support from
> +         filesystem side. For now, the only filesystem which supports
> +         hugepages is ramfs.
> +
>  config CROSS_MEMORY_ATTACH
>         bool "Cross Memory Support"
>         depends on MMU
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index d96d921..523946c 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -42,6 +42,9 @@ unsigned long transparent_hugepage_flags __read_mostly =
>  #endif
>         (1<<TRANSPARENT_HUGEPAGE_DEFRAG_FLAG)|
>         (1<<TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG)|
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE_PAGECACHE
> +       (1<<TRANSPARENT_HUGEPAGE_PAGECACHE)|
> +#endif
>         (1<<TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
>
>  /* default scan 8*512 pte (or vmas) every 30 second */
> @@ -362,6 +365,23 @@ static ssize_t defrag_store(struct kobject *kobj,
>  static struct kobj_attribute defrag_attr =
>         __ATTR(defrag, 0644, defrag_show, defrag_store);
>
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE_PAGECACHE
> +static ssize_t page_cache_show(struct kobject *kobj,
> +               struct kobj_attribute *attr, char *buf)
> +{
> +       return single_flag_show(kobj, attr, buf,
> +                               TRANSPARENT_HUGEPAGE_PAGECACHE);
> +}
> +static ssize_t page_cache_store(struct kobject *kobj,
> +               struct kobj_attribute *attr, const char *buf, size_t count)
> +{
> +       return single_flag_store(kobj, attr, buf, count,
> +                                TRANSPARENT_HUGEPAGE_PAGECACHE);
> +}
> +static struct kobj_attribute page_cache_attr =
> +       __ATTR(page_cache, 0644, page_cache_show, page_cache_store);
> +#endif
> +
>  static ssize_t use_zero_page_show(struct kobject *kobj,
>                 struct kobj_attribute *attr, char *buf)
>  {
> @@ -397,6 +417,9 @@ static struct kobj_attribute debug_cow_attr =
>  static struct attribute *hugepage_attr[] = {
>         &enabled_attr.attr,
>         &defrag_attr.attr,
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE_PAGECACHE
> +       &page_cache_attr.attr,
> +#endif
>         &use_zero_page_attr.attr,
>  #ifdef CONFIG_DEBUG_VM
>         &debug_cow_attr.attr,
> --
> 1.8.3.2
>
>

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