Messages in this thread | | | Subject | Re: [PATCH 14/16] mm/thp: add THP allocation helper | From | Ralph Campbell <> | Date | Mon, 22 Jun 2020 14:33:06 -0700 |
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On 6/21/20 5:15 PM, Zi Yan wrote: > 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 >
Oops, I'm not sure why I thought that was needed. The whole file is only compiled if CONFIG_TRANSPARENT_HUGEPAGE is defined and the calls to alloc_hugepage_vma() and alloc_hugepage_direct_gfpmask() are unprotected just above this in do_huge_pmd_anonymous_page(). I'll fix that in v2.
The helper is intended to be called by a device driver to allocate a THP when migrating device private memory back to system memory. The THP should never be migrated to device private memory in the first place if transparent_hugepage_enabled(vma) is false. I suppose I could add a if (WARN_ON_ONCE()) return NULL as a sanity check. The real checks are in migrate_vma_setup() and migrate_vma_pages().
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