Re: [PATCH 14/16] mm/thp: add THP allocation helper

From: Zi Yan <ziy@nvidia.com>
To: Ralph Campbell <rcampbell@nvidia.com>
Cc: <nouveau@lists.freedesktop.org>, <linux-rdma@vger.kernel.org>,
	<linux-mm@kvack.org>, <linux-kselftest@vger.kernel.org>,
	<linux-kernel@vger.kernel.org>,
	Jerome Glisse <jglisse@redhat.com>,
	"John Hubbard" <jhubbard@nvidia.com>,
	Christoph Hellwig <hch@lst.de>,
	"Jason Gunthorpe" <jgg@mellanox.com>,
	Ben Skeggs <bskeggs@redhat.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Shuah Khan <shuah@kernel.org>
Subject: Re: [PATCH 14/16] mm/thp: add THP allocation helper
Date: Sun, 21 Jun 2020 20:15:45 -0400	[thread overview]
Message-ID: <9948121A-CA52-494F-9B68-6C0089E15057@nvidia.com> (raw)
In-Reply-To: <20200619215649.32297-15-rcampbell@nvidia.com>

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On 19 Jun 2020, at 17:56, Ralph Campbell wrote:

> Transparent huge page allocation policy is controlled by several sysfs
> variables. Rather than expose these to each device driver that needs to
> allocate THPs, provide a helper function.
>
> Signed-off-by: Ralph Campbell <rcampbell@nvidia.com>
> ---
>  include/linux/gfp.h | 10 ++++++++++
>  mm/huge_memory.c    | 16 ++++++++++++++++
>  2 files changed, 26 insertions(+)
>
> diff --git a/include/linux/gfp.h b/include/linux/gfp.h
> index 67a0774e080b..1c7d968a27d3 100644
> --- a/include/linux/gfp.h
> +++ b/include/linux/gfp.h
> @@ -562,6 +562,16 @@ extern struct page *alloc_pages_vma(gfp_t gfp_mask, int order,
>  	alloc_pages_vma(gfp_mask, 0, vma, addr, numa_node_id(), false)
>  #define alloc_page_vma_node(gfp_mask, vma, addr, node)		\
>  	alloc_pages_vma(gfp_mask, 0, vma, addr, node, false)
> +#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
> +extern struct page *alloc_transhugepage(struct vm_area_struct *vma,
> +					unsigned long addr);
> +#else
> +static inline struct page *alloc_transhugepage(struct vm_area_struct *vma,
> +						unsigned long addr)
> +{
> +	return NULL;
> +}
> +#endif
>
>  extern unsigned long __get_free_pages(gfp_t gfp_mask, unsigned int order);
>  extern unsigned long get_zeroed_page(gfp_t gfp_mask);
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 25d95f7b1e98..f749633ed350 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -775,6 +775,22 @@ vm_fault_t do_huge_pmd_anonymous_page(struct vm_fault *vmf)
>  	return __do_huge_pmd_anonymous_page(vmf, page, gfp);
>  }
>
> +#ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
> +struct page *alloc_transhugepage(struct vm_area_struct *vma,
> +				 unsigned long haddr)
> +{
> +	gfp_t gfp;
> +	struct page *page;
> +
> +	gfp = alloc_hugepage_direct_gfpmask(vma);
> +	page = alloc_hugepage_vma(gfp, vma, haddr, HPAGE_PMD_ORDER);
> +	if (page)
> +		prep_transhuge_page(page);
> +	return page;
> +}
> +EXPORT_SYMBOL_GPL(alloc_transhugepage);
> +#endif
> +
>  static void insert_pfn_pmd(struct vm_area_struct *vma, unsigned long addr,
>  		pmd_t *pmd, pfn_t pfn, pgprot_t prot, bool write,
>  		pgtable_t pgtable)
> -- 
> 2.20.1

Why use CONFIG_ARCH_ENABLE_THP_MIGRATION to guard THP allocator helper?
Shouldn’t CONFIG_TRANSPARENT_HUGEPAGE be used? Also the helper still allocates
a THP even if transparent_hugepage_enabled(vma) is false, which is wrong, right?

--
Best Regards,
Yan Zi

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