RE: [PATCH] Make transparent hugepages cpuset aware

[Kirill A. Shutemov]

Alex Thorlton wrote:
> This patch adds the ability to control THPs on a per cpuset basis.  Please see
> the additions to Documentation/cgroups/cpusets.txt for more information.
> 
> Signed-off-by: Alex Thorlton <athorlton@xxxxxxx>
> Reviewed-by: Robin Holt <holt@xxxxxxx>
> Cc: Li Zefan <lizefan@xxxxxxxxxx>
> Cc: Rob Landley <rob@xxxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Mel Gorman <mgorman@xxxxxxx>
> Cc: Rik van Riel <riel@xxxxxxxxxx>
> Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> Cc: Xiao Guangrong <xiaoguangrong@xxxxxxxxxxxxxxxxxx>
> Cc: David Rientjes <rientjes@xxxxxxxxxx>
> Cc: linux-doc@xxxxxxxxxxxxxxx
> Cc: linux-mm@xxxxxxxxx
> ---
>  Documentation/cgroups/cpusets.txt |  50 ++++++++++-
>  include/linux/cpuset.h            |   5 ++
>  include/linux/huge_mm.h           |  25 +++++-
>  kernel/cpuset.c                   | 181 ++++++++++++++++++++++++++++++++++++++
>  mm/huge_memory.c                  |   3 +
>  5 files changed, 261 insertions(+), 3 deletions(-)
> 
> diff --git a/Documentation/cgroups/cpusets.txt b/Documentation/cgroups/cpusets.txt
> index 12e01d4..b7b2c83 100644
> --- a/Documentation/cgroups/cpusets.txt
> +++ b/Documentation/cgroups/cpusets.txt
> @@ -22,12 +22,14 @@ CONTENTS:
>    1.6 What is memory spread ?
>    1.7 What is sched_load_balance ?
>    1.8 What is sched_relax_domain_level ?
> -  1.9 How do I use cpusets ?
> +  1.9 What is thp_enabled ?
> +  1.10 How do I use cpusets ?
>  2. Usage Examples and Syntax
>    2.1 Basic Usage
>    2.2 Adding/removing cpus
>    2.3 Setting flags
>    2.4 Attaching processes
> +  2.5 Setting thp_enabled flags
>  3. Questions
>  4. Contact
>  
> @@ -581,7 +583,34 @@ If your situation is:
>  then increasing 'sched_relax_domain_level' would benefit you.
>  
>  
> -1.9 How do I use cpusets ?
> +1.9 What is thp_enabled ?
> +-----------------------
> +
> +The thp_enabled file contained within each cpuset controls how transparent
> +hugepages are handled within that cpuset.
> +
> +The root cpuset's thp_enabled flags mirror the flags set in
> +/sys/kernel/mm/transparent_hugepage/enabled.  The flags in the root cpuset can
> +only be modified by changing /sys/kernel/mm/transparent_hugepage/enabled. The
> +thp_enabled file for the root cpuset is read only.  These flags cause the
> +root cpuset to behave as one might expect:
> +
> +- When set to always, THPs are used whenever practical
> +- When set to madvise, THPs are used only on chunks of memory that have the
> +  MADV_HUGEPAGE flag set
> +- When set to never, THPs are never allowed for tasks in this cpuset
> +
> +The behavior of thp_enabled for children of the root cpuset is where things
> +become a bit more interesting.  The child cpusets accept the same flags as the
> +root, but also have a default flag, which, when set, causes a cpuset to use the
> +behavior of its parent.  When a child cpuset is created, its default flag is
> +always initially set.
> +
> +Since the flags on child cpusets are allowed to differ from the flags on their
> +parents, we are able to enable THPs for tasks in specific cpusets, and disable
> +them in others.

Should we have a way for parent cgroup can enforce child behaviour?
Like a mask of allowed thp_enabled values children can choose.

> @@ -177,6 +177,29 @@ static inline struct page *compound_trans_head(struct page *page)
>  	return page;
>  }
>  
> +#ifdef CONFIG_CPUSETS
> +extern int cpuset_thp_always(struct task_struct *p);
> +extern int cpuset_thp_madvise(struct task_struct *p);
> +
> +static inline int transparent_hugepage_enabled(struct vm_area_struct *vma)
> +{
> +	if (cpuset_thp_always(current))
> +		return 1;

Why do you ignore VM_NOHUGEPAGE?
And !is_vma_temporary_stack(__vma) is still relevant.

> +	else if (cpuset_thp_madvise(current) &&
> +		 ((vma)->vm_flags & VM_HUGEPAGE) &&
> +		 !((vma)->vm_flags & VM_NOHUGEPAGE) &&
> +		 !is_vma_temporary_stack(vma))
> +		return 1;
> +	else
> +		return 0;
> +}
> +#else
> +static inline int transparent_hugepage_enabled(struct vm_area_struct *vma)
> +{
> +	return _transparent_hugepage_enabled(vma);
> +}
> +#endif
> +
>  extern int do_huge_pmd_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,
>  				unsigned long addr, pmd_t pmd, pmd_t *pmdp);
>  

-- 
 Kirill A. Shutemov
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