linux-kernel - Re: [PATCH] mm: khugepaged: decouple SHMEM and file folios' collapse

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Message-ID: <6629D237-A86B-4447-ADB1-FCAC352D4D40@nvidia.com>
Date: Tue, 13 May 2025 11:04:01 -0400
From: Zi Yan <ziy@...dia.com>
To: Baolin Wang <baolin.wang@...ux.alibaba.com>,
 Song Liu <songliubraving@...com>
Cc: akpm@...ux-foundation.org, david@...hat.com, lorenzo.stoakes@...cle.com,
 Liam.Howlett@...cle.com, npache@...hat.com, ryan.roberts@....com,
 dev.jain@....com, vbabka@...e.cz, rppt@...nel.org, surenb@...gle.com,
 mhocko@...e.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: khugepaged: decouple SHMEM and file folios' collapse

On 13 May 2025, at 2:56, Baolin Wang wrote:

> Originally, the file pages collapse was intended for tmpfs/shmem to merge
> into THP in the background. However, now not only tmpfs/shmem can support
> large folios, but some other file systems (such as XFS, erofs ...) also
> support large folios. Therefore, it is time to decouple the support of
> file folios collapse from SHMEM.
>
> Signed-off-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
> Acked-by: David Hildenbrand <david@...hat.com>
> ---
> Changes from RFC:
>  - Add acked tag from David. Thanks.
>  - Remove CONFIG_SHMEM in khugepaged.h file.
> ---
>  include/linux/khugepaged.h |  8 --------
>  mm/Kconfig                 |  2 +-
>  mm/khugepaged.c            | 13 ++-----------
>  3 files changed, 3 insertions(+), 20 deletions(-)

+Song, the author of READ_ONLY_THP_FOR_FS.

The changes look good to me. Acked-by: Zi Yan <ziy@...dia.com>

>
> diff --git a/include/linux/khugepaged.h b/include/linux/khugepaged.h
> index 1f46046080f5..b8d69cfbb58b 100644
> --- a/include/linux/khugepaged.h
> +++ b/include/linux/khugepaged.h
> @@ -15,16 +15,8 @@ extern void khugepaged_enter_vma(struct vm_area_struct *vma,
>  				 unsigned long vm_flags);
>  extern void khugepaged_min_free_kbytes_update(void);
>  extern bool current_is_khugepaged(void);
> -#ifdef CONFIG_SHMEM
>  extern int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr,
>  				   bool install_pmd);
> -#else
> -static inline int collapse_pte_mapped_thp(struct mm_struct *mm,
> -					  unsigned long addr, bool install_pmd)
> -{
> -	return 0;
> -}
> -#endif
>
>  static inline void khugepaged_fork(struct mm_struct *mm, struct mm_struct *oldmm)
>  {
> diff --git a/mm/Kconfig b/mm/Kconfig
> index d4fd40f56178..79237842f7e2 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -898,7 +898,7 @@ config THP_SWAP
>
>  config READ_ONLY_THP_FOR_FS
>  	bool "Read-only THP for filesystems (EXPERIMENTAL)"
> -	depends on TRANSPARENT_HUGEPAGE && SHMEM
> +	depends on TRANSPARENT_HUGEPAGE
>
>  	help
>  	  Allow khugepaged to put read-only file-backed pages in THP.
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index ebcd7c8a4b44..cdf5a581368b 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -1464,7 +1464,6 @@ static void collect_mm_slot(struct khugepaged_mm_slot *mm_slot)
>  	}
>  }
>
> -#ifdef CONFIG_SHMEM
>  /* folio must be locked, and mmap_lock must be held */
>  static int set_huge_pmd(struct vm_area_struct *vma, unsigned long addr,
>  			pmd_t *pmdp, struct folio *folio, struct page *page)
> @@ -2353,14 +2352,6 @@ static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr,
>  	trace_mm_khugepaged_scan_file(mm, folio, file, present, swap, result);
>  	return result;
>  }
> -#else
> -static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr,
> -				    struct file *file, pgoff_t start,
> -				    struct collapse_control *cc)
> -{
> -	BUILD_BUG();
> -}
> -#endif
>
>  static unsigned int khugepaged_scan_mm_slot(unsigned int pages, int *result,
>  					    struct collapse_control *cc)
> @@ -2436,7 +2427,7 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages, int *result,
>  			VM_BUG_ON(khugepaged_scan.address < hstart ||
>  				  khugepaged_scan.address + HPAGE_PMD_SIZE >
>  				  hend);
> -			if (IS_ENABLED(CONFIG_SHMEM) && !vma_is_anonymous(vma)) {
> +			if (!vma_is_anonymous(vma)) {
>  				struct file *file = get_file(vma->vm_file);
>  				pgoff_t pgoff = linear_page_index(vma,
>  						khugepaged_scan.address);
> @@ -2782,7 +2773,7 @@ int madvise_collapse(struct vm_area_struct *vma, struct vm_area_struct **prev,
>  		mmap_assert_locked(mm);
>  		memset(cc->node_load, 0, sizeof(cc->node_load));
>  		nodes_clear(cc->alloc_nmask);
> -		if (IS_ENABLED(CONFIG_SHMEM) && !vma_is_anonymous(vma)) {
> +		if (!vma_is_anonymous(vma)) {
>  			struct file *file = get_file(vma->vm_file);
>  			pgoff_t pgoff = linear_page_index(vma, addr);
>
> -- 
> 2.43.5


Best Regards,
Yan, Zi