Date:   Tue, 17 Oct 2017 12:20:52 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     changbin.du@...el.com
Cc:     akpm@...ux-foundation.org, corbet@....net, hughd@...gle.com,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH 1/2] mm, thp: introduce dedicated transparent huge page
 allocation interfaces

[CC Kirill]

On Mon 16-10-17 17:19:16, changbin.du@...el.com wrote:
> From: Changbin Du <changbin.du@...el.com>
> 
> This patch introduced 4 new interfaces to allocate a prepared
> transparent huge page.
>   - alloc_transhuge_page_vma
>   - alloc_transhuge_page_nodemask
>   - alloc_transhuge_page_node
>   - alloc_transhuge_page
> 
> The aim is to remove duplicated code and simplify transparent
> huge page allocation. These are similar to alloc_hugepage_xxx
> which are for hugetlbfs pages. This patch does below changes:
>   - define alloc_transhuge_page_xxx interfaces
>   - apply them to all existing code
>   - declare prep_transhuge_page as static since no others use it
>   - remove alloc_hugepage_vma definition since it no longer has users

So what exactly is the advantage of the new API? The diffstat doesn't
sound very convincing to me.

> Signed-off-by: Changbin Du <changbin.du@...el.com>
> ---
>  include/linux/gfp.h     |  4 ----
>  include/linux/huge_mm.h | 13 ++++++++++++-
>  include/linux/migrate.h | 14 +++++---------
>  mm/huge_memory.c        | 50 ++++++++++++++++++++++++++++++++++++++++++-------
>  mm/khugepaged.c         | 11 ++---------
>  mm/mempolicy.c          | 10 +++-------
>  mm/migrate.c            | 12 ++++--------
>  mm/shmem.c              |  6 ++----
>  8 files changed, 71 insertions(+), 49 deletions(-)
> 
> diff --git a/include/linux/gfp.h b/include/linux/gfp.h
> index f780718..855c72e 100644
> --- a/include/linux/gfp.h
> +++ b/include/linux/gfp.h
> @@ -507,15 +507,11 @@ alloc_pages(gfp_t gfp_mask, unsigned int order)
>  extern struct page *alloc_pages_vma(gfp_t gfp_mask, int order,
>  			struct vm_area_struct *vma, unsigned long addr,
>  			int node, bool hugepage);
> -#define alloc_hugepage_vma(gfp_mask, vma, addr, order)	\
> -	alloc_pages_vma(gfp_mask, order, vma, addr, numa_node_id(), true)
>  #else
>  #define alloc_pages(gfp_mask, order) \
>  		alloc_pages_node(numa_node_id(), gfp_mask, order)
>  #define alloc_pages_vma(gfp_mask, order, vma, addr, node, false)\
>  	alloc_pages(gfp_mask, order)
> -#define alloc_hugepage_vma(gfp_mask, vma, addr, order)	\
> -	alloc_pages(gfp_mask, order)
>  #endif
>  #define alloc_page(gfp_mask) alloc_pages(gfp_mask, 0)
>  #define alloc_page_vma(gfp_mask, vma, addr)			\
> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> index 14bc21c..1dd2c33 100644
> --- a/include/linux/huge_mm.h
> +++ b/include/linux/huge_mm.h
> @@ -130,9 +130,20 @@ extern unsigned long thp_get_unmapped_area(struct file *filp,
>  		unsigned long addr, unsigned long len, unsigned long pgoff,
>  		unsigned long flags);
>  
> -extern void prep_transhuge_page(struct page *page);
>  extern void free_transhuge_page(struct page *page);
>  
> +struct page *alloc_transhuge_page_vma(gfp_t gfp_mask,
> +		struct vm_area_struct *vma, unsigned long addr);
> +struct page *alloc_transhuge_page_nodemask(gfp_t gfp_mask,
> +		int preferred_nid, nodemask_t *nmask);
> +
> +static inline struct page *alloc_transhuge_page_node(int nid, gfp_t gfp_mask)
> +{
> +	return alloc_transhuge_page_nodemask(gfp_mask, nid, NULL);
> +}
> +
> +struct page *alloc_transhuge_page(gfp_t gfp_mask);
> +
>  bool can_split_huge_page(struct page *page, int *pextra_pins);
>  int split_huge_page_to_list(struct page *page, struct list_head *list);
>  static inline int split_huge_page(struct page *page)
> diff --git a/include/linux/migrate.h b/include/linux/migrate.h
> index 643c7ae..70a00f3 100644
> --- a/include/linux/migrate.h
> +++ b/include/linux/migrate.h
> @@ -42,19 +42,15 @@ static inline struct page *new_page_nodemask(struct page *page,
>  		return alloc_huge_page_nodemask(page_hstate(compound_head(page)),
>  				preferred_nid, nodemask);
>  
> -	if (thp_migration_supported() && PageTransHuge(page)) {
> -		order = HPAGE_PMD_ORDER;
> -		gfp_mask |= GFP_TRANSHUGE;
> -	}
> -
>  	if (PageHighMem(page) || (zone_idx(page_zone(page)) == ZONE_MOVABLE))
>  		gfp_mask |= __GFP_HIGHMEM;
>  
> -	new_page = __alloc_pages_nodemask(gfp_mask, order,
> +	if (thp_migration_supported() && PageTransHuge(page))
> +		return alloc_transhuge_page_nodemask(gfp_mask | GFP_TRANSHUGE,
> +				preferred_nid, nodemask);
> +	else
> +		return __alloc_pages_nodemask(gfp_mask, order,
>  				preferred_nid, nodemask);
> -
> -	if (new_page && PageTransHuge(page))
> -		prep_transhuge_page(new_page);
>  
>  	return new_page;
>  }
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 269b5df..e267488 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -490,7 +490,7 @@ static inline struct list_head *page_deferred_list(struct page *page)
>  	return (struct list_head *)&page[2].mapping;
>  }
>  
> -void prep_transhuge_page(struct page *page)
> +static void prep_transhuge_page(struct page *page)
>  {
>  	/*
>  	 * we use page->mapping and page->indexlru in second tail page
> @@ -501,6 +501,45 @@ void prep_transhuge_page(struct page *page)
>  	set_compound_page_dtor(page, TRANSHUGE_PAGE_DTOR);
>  }
>  
> +struct page *alloc_transhuge_page_vma(gfp_t gfp_mask,
> +		struct vm_area_struct *vma, unsigned long addr)
> +{
> +	struct page *page;
> +
> +	page = alloc_pages_vma(gfp_mask | __GFP_COMP, HPAGE_PMD_ORDER,
> +			       vma, addr, numa_node_id(), true);
> +	if (unlikely(!page))
> +		return NULL;
> +	prep_transhuge_page(page);
> +	return page;
> +}
> +
> +struct page *alloc_transhuge_page_nodemask(gfp_t gfp_mask,
> +		int preferred_nid, nodemask_t *nmask)
> +{
> +	struct page *page;
> +
> +	page = __alloc_pages_nodemask(gfp_mask | __GFP_COMP, HPAGE_PMD_ORDER,
> +				      preferred_nid, nmask);
> +	if (unlikely(!page))
> +		return NULL;
> +	prep_transhuge_page(page);
> +	return page;
> +}
> +
> +struct page *alloc_transhuge_page(gfp_t gfp_mask)
> +{
> +	struct page *page;
> +
> +	VM_BUG_ON(!(gfp_mask & __GFP_COMP));
> +
> +	page = alloc_pages(gfp_mask | __GFP_COMP, HPAGE_PMD_ORDER);
> +	if (unlikely(!page))
> +		return NULL;
> +	prep_transhuge_page(page);
> +	return page;
> +}
> +
>  unsigned long __thp_get_unmapped_area(struct file *filp, unsigned long len,
>  		loff_t off, unsigned long flags, unsigned long size)
>  {
> @@ -719,12 +758,11 @@ int do_huge_pmd_anonymous_page(struct vm_fault *vmf)
>  		return ret;
>  	}
>  	gfp = alloc_hugepage_direct_gfpmask(vma);
> -	page = alloc_hugepage_vma(gfp, vma, haddr, HPAGE_PMD_ORDER);
> +	page = alloc_transhuge_page_vma(gfp, vma, haddr);
>  	if (unlikely(!page)) {
>  		count_vm_event(THP_FAULT_FALLBACK);
>  		return VM_FAULT_FALLBACK;
>  	}
> -	prep_transhuge_page(page);
>  	return __do_huge_pmd_anonymous_page(vmf, page, gfp);
>  }
>  
> @@ -1288,13 +1326,11 @@ int do_huge_pmd_wp_page(struct vm_fault *vmf, pmd_t orig_pmd)
>  	if (transparent_hugepage_enabled(vma) &&
>  	    !transparent_hugepage_debug_cow()) {
>  		huge_gfp = alloc_hugepage_direct_gfpmask(vma);
> -		new_page = alloc_hugepage_vma(huge_gfp, vma, haddr, HPAGE_PMD_ORDER);
> +		new_page = alloc_transhuge_page_vma(huge_gfp, vma, haddr);
>  	} else
>  		new_page = NULL;
>  
> -	if (likely(new_page)) {
> -		prep_transhuge_page(new_page);
> -	} else {
> +	if (unlikely(!new_page)) {
>  		if (!page) {
>  			split_huge_pmd(vma, vmf->pmd, vmf->address);
>  			ret |= VM_FAULT_FALLBACK;
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index c01f177..d17a694 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -745,14 +745,13 @@ khugepaged_alloc_page(struct page **hpage, gfp_t gfp, int node)
>  {
>  	VM_BUG_ON_PAGE(*hpage, *hpage);
>  
> -	*hpage = __alloc_pages_node(node, gfp, HPAGE_PMD_ORDER);
> +	*hpage = alloc_transhuge_page_node(node, gfp);
>  	if (unlikely(!*hpage)) {
>  		count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
>  		*hpage = ERR_PTR(-ENOMEM);
>  		return NULL;
>  	}
>  
> -	prep_transhuge_page(*hpage);
>  	count_vm_event(THP_COLLAPSE_ALLOC);
>  	return *hpage;
>  }
> @@ -764,13 +763,7 @@ static int khugepaged_find_target_node(void)
>  
>  static inline struct page *alloc_khugepaged_hugepage(void)
>  {
> -	struct page *page;
> -
> -	page = alloc_pages(alloc_hugepage_khugepaged_gfpmask(),
> -			   HPAGE_PMD_ORDER);
> -	if (page)
> -		prep_transhuge_page(page);
> -	return page;
> +	return alloc_transhuge_page(alloc_hugepage_khugepaged_gfpmask());
>  }
>  
>  static struct page *khugepaged_alloc_hugepage(bool *wait)
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index a2af6d5..aa24285 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -949,12 +949,10 @@ static struct page *new_node_page(struct page *page, unsigned long node, int **x
>  	else if (thp_migration_supported() && PageTransHuge(page)) {
>  		struct page *thp;
>  
> -		thp = alloc_pages_node(node,
> -			(GFP_TRANSHUGE | __GFP_THISNODE),
> -			HPAGE_PMD_ORDER);
> +		thp = alloc_transhuge_page_node(node,
> +			(GFP_TRANSHUGE | __GFP_THISNODE));
>  		if (!thp)
>  			return NULL;
> -		prep_transhuge_page(thp);
>  		return thp;
>  	} else
>  		return __alloc_pages_node(node, GFP_HIGHUSER_MOVABLE |
> @@ -1125,11 +1123,9 @@ static struct page *new_page(struct page *page, unsigned long start, int **x)
>  	} else if (thp_migration_supported() && PageTransHuge(page)) {
>  		struct page *thp;
>  
> -		thp = alloc_hugepage_vma(GFP_TRANSHUGE, vma, address,
> -					 HPAGE_PMD_ORDER);
> +		thp = alloc_transhuge_page_vma(GFP_TRANSHUGE, vma, address);
>  		if (!thp)
>  			return NULL;
> -		prep_transhuge_page(thp);
>  		return thp;
>  	}
>  	/*
> diff --git a/mm/migrate.c b/mm/migrate.c
> index e00814c..7f0486f 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1472,12 +1472,10 @@ static struct page *new_page_node(struct page *p, unsigned long private,
>  	else if (thp_migration_supported() && PageTransHuge(p)) {
>  		struct page *thp;
>  
> -		thp = alloc_pages_node(pm->node,
> -			(GFP_TRANSHUGE | __GFP_THISNODE) & ~__GFP_RECLAIM,
> -			HPAGE_PMD_ORDER);
> +		thp = alloc_transhuge_page_node(pm->node,
> +			(GFP_TRANSHUGE | __GFP_THISNODE) & ~__GFP_RECLAIM);
>  		if (!thp)
>  			return NULL;
> -		prep_transhuge_page(thp);
>  		return thp;
>  	} else
>  		return __alloc_pages_node(pm->node,
> @@ -2017,12 +2015,10 @@ int migrate_misplaced_transhuge_page(struct mm_struct *mm,
>  	if (numamigrate_update_ratelimit(pgdat, HPAGE_PMD_NR))
>  		goto out_dropref;
>  
> -	new_page = alloc_pages_node(node,
> -		(GFP_TRANSHUGE_LIGHT | __GFP_THISNODE),
> -		HPAGE_PMD_ORDER);
> +	new_page = alloc_transhuge_page_node(node,
> +			(GFP_TRANSHUGE_LIGHT | __GFP_THISNODE));
>  	if (!new_page)
>  		goto out_fail;
> -	prep_transhuge_page(new_page);
>  
>  	isolated = numamigrate_isolate_page(pgdat, page);
>  	if (!isolated) {
> diff --git a/mm/shmem.c b/mm/shmem.c
> index 07a1d22..52468f7 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -1444,11 +1444,9 @@ static struct page *shmem_alloc_hugepage(gfp_t gfp,
>  	rcu_read_unlock();
>  
>  	shmem_pseudo_vma_init(&pvma, info, hindex);
> -	page = alloc_pages_vma(gfp | __GFP_COMP | __GFP_NORETRY | __GFP_NOWARN,
> -			HPAGE_PMD_ORDER, &pvma, 0, numa_node_id(), true);
> +	gfp |= __GFP_COMP | __GFP_NORETRY | __GFP_NOWARN;
> +	page = alloc_transhuge_page_vma(gfp, &pvma, 0);
>  	shmem_pseudo_vma_destroy(&pvma);
> -	if (page)
> -		prep_transhuge_page(page);
>  	return page;
>  }
>  
> -- 
> 2.7.4
> 
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-- 
Michal Hocko
SUSE Labs

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