linux-kernel - Re: [v3 PATCH 6/8] mm: khugepaged: move some khugepaged

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Message-ID: <f304299d-e533-ed18-e247-6dec928ce3b0@suse.cz>
Date:   Mon, 9 May 2022 17:31:08 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Yang Shi <shy828301@...il.com>, kirill.shutemov@...ux.intel.com,
        linmiaohe@...wei.com, songliubraving@...com, riel@...riel.com,
        willy@...radead.org, ziy@...dia.com, tytso@....edu,
        akpm@...ux-foundation.org
Cc:     linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [v3 PATCH 6/8] mm: khugepaged: move some khugepaged_* functions
 to khugepaged.c

On 4/4/22 22:02, Yang Shi wrote:
> To reuse hugepage_vma_check() for khugepaged_enter() so that we could
> remove some duplicate code.  But moving hugepage_vma_check() to
> khugepaged.h needs to include huge_mm.h in it, it seems not optimal to
> bloat khugepaged.h.
> 
> And the khugepaged_* functions actually are wrappers for some non-inline
> functions, so it seems the benefits are not too much to keep them inline.
> 
> So move the khugepaged_* functions to khugepaged.c, any callers just
> need to include khugepaged.h which is quite small.  For example, the
> following patches will call khugepaged_enter() in filemap page fault path
> for regular filesystems to make readonly FS THP collapse more consistent.
> The  filemap.c just needs to include khugepaged.h.

This last part is inaccurate in v3?

> Acked-by: Song Liu <song@...nel.org>
> Signed-off-by: Yang Shi <shy828301@...il.com>

I think moving the tiny wrappers is unnecessary.

How about just making hugepage_vma_check() not static and declare it in
khugepaged.h, then it can be used from khugepaged_enter() in the same file
and AFAICS no need to include huge_mm.h there?

> ---
>  include/linux/khugepaged.h | 37 ++++++-------------------------------
>  mm/khugepaged.c            | 20 ++++++++++++++++++++
>  2 files changed, 26 insertions(+), 31 deletions(-)
> 
> diff --git a/include/linux/khugepaged.h b/include/linux/khugepaged.h
> index 0423d3619f26..6acf9701151e 100644
> --- a/include/linux/khugepaged.h
> +++ b/include/linux/khugepaged.h
> @@ -2,10 +2,6 @@
>  #ifndef _LINUX_KHUGEPAGED_H
>  #define _LINUX_KHUGEPAGED_H
>  
> -#include <linux/sched/coredump.h> /* MMF_VM_HUGEPAGE */
> -#include <linux/shmem_fs.h>
> -
> -
>  #ifdef CONFIG_TRANSPARENT_HUGEPAGE
>  extern struct attribute_group khugepaged_attr_group;
>  
> @@ -16,6 +12,12 @@ extern void __khugepaged_enter(struct mm_struct *mm);
>  extern void __khugepaged_exit(struct mm_struct *mm);
>  extern void khugepaged_enter_vma_merge(struct vm_area_struct *vma,
>  				       unsigned long vm_flags);
> +extern void khugepaged_fork(struct mm_struct *mm,
> +			    struct mm_struct *oldmm);
> +extern void khugepaged_exit(struct mm_struct *mm);
> +extern void khugepaged_enter(struct vm_area_struct *vma,
> +			     unsigned long vm_flags);
> +
>  extern void khugepaged_min_free_kbytes_update(void);
>  #ifdef CONFIG_SHMEM
>  extern void collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr);
> @@ -33,36 +35,9 @@ static inline void collapse_pte_mapped_thp(struct mm_struct *mm,
>  #define khugepaged_always()				\
>  	(transparent_hugepage_flags &			\
>  	 (1<<TRANSPARENT_HUGEPAGE_FLAG))
> -#define khugepaged_req_madv()					\
> -	(transparent_hugepage_flags &				\
> -	 (1<<TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG))
>  #define khugepaged_defrag()					\
>  	(transparent_hugepage_flags &				\
>  	 (1<<TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG))
> -
> -static inline void khugepaged_fork(struct mm_struct *mm, struct mm_struct *oldmm)
> -{
> -	if (test_bit(MMF_VM_HUGEPAGE, &oldmm->flags))
> -		__khugepaged_enter(mm);
> -}
> -
> -static inline void khugepaged_exit(struct mm_struct *mm)
> -{
> -	if (test_bit(MMF_VM_HUGEPAGE, &mm->flags))
> -		__khugepaged_exit(mm);
> -}
> -
> -static inline void khugepaged_enter(struct vm_area_struct *vma,
> -				   unsigned long vm_flags)
> -{
> -	if (!test_bit(MMF_VM_HUGEPAGE, &vma->vm_mm->flags))
> -		if ((khugepaged_always() ||
> -		     (shmem_file(vma->vm_file) && shmem_huge_enabled(vma)) ||
> -		     (khugepaged_req_madv() && (vm_flags & VM_HUGEPAGE))) &&
> -		    !(vm_flags & VM_NOHUGEPAGE) &&
> -		    !test_bit(MMF_DISABLE_THP, &vma->vm_mm->flags))
> -			__khugepaged_enter(vma->vm_mm);
> -}
>  #else /* CONFIG_TRANSPARENT_HUGEPAGE */
>  static inline void khugepaged_fork(struct mm_struct *mm, struct mm_struct *oldmm)
>  {
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index b69eda934d70..ec5b0a691d87 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -556,6 +556,26 @@ void __khugepaged_exit(struct mm_struct *mm)
>  	}
>  }
>  
> +void khugepaged_fork(struct mm_struct *mm, struct mm_struct *oldmm)
> +{
> +	if (test_bit(MMF_VM_HUGEPAGE, &oldmm->flags))
> +		__khugepaged_enter(mm);
> +}
> +
> +void khugepaged_exit(struct mm_struct *mm)
> +{
> +	if (test_bit(MMF_VM_HUGEPAGE, &mm->flags))
> +		__khugepaged_exit(mm);
> +}
> +
> +void khugepaged_enter(struct vm_area_struct *vma, unsigned long vm_flags)
> +{
> +	if (!test_bit(MMF_VM_HUGEPAGE, &vma->vm_mm->flags) &&
> +	    khugepaged_enabled())
> +		if (hugepage_vma_check(vma, vm_flags))
> +			__khugepaged_enter(vma->vm_mm);
> +}
> +
>  static void release_pte_page(struct page *page)
>  {
>  	mod_node_page_state(page_pgdat(page),