linux-kernel - Re: [RFC PATCH 1/3] mm/thp: Use pmdp_splitting_flush

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Message-ID: <87fv7h36nr.fsf@linux.vnet.ibm.com>
Date:	Thu, 30 Apr 2015 22:17:04 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	"Kirill A. Shutemov" <kirill@...temov.name>
Cc:	akpm@...ux-foundation.org, paulus@...ba.org,
	benh@...nel.crashing.org, kirill.shutemov@...ux.intel.com,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 1/3] mm/thp: Use pmdp_splitting_flush_notify to clear pmd on splitting

"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com> writes:

> "Kirill A. Shutemov" <kirill@...temov.name> writes:
>
>>> @@ -184,3 +185,13 @@ void pmdp_invalidate(struct vm_area_struct *vma, unsigned long address,
>>>  }
>>>  #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
>>>  #endif
>>> +
>>> +#ifndef __HAVE_ARCH_PMDP_SPLITTING_FLUSH_NOTIFY
>>> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
>>> +void pmdp_splitting_flush_notify(struct vm_area_struct *vma,
>>> +				 unsigned long address, pmd_t *pmdp)
>>> +{
>>> +	pmdp_clear_flush_notify(vma, address, pmdp);
>>> +}
>>> +#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
>>> +#endif
>>
>> I think it worth inlining. Let's put it to <asm-generic/pgtable.h>
>>
>> It probably worth combining with collapse counterpart in the same patch.
>>
>
> I tried that first, But that pulls in mmu_notifier.h and huge_mm.h
> headers and other build failures
>

Putting them in TRANSPATENT_HUGEPAGE helped.

commit 9c60ab5d1d684db2ba454ee1c7f3e9a6bf57f026
Author: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
Date:   Wed Apr 29 14:57:30 2015 +0530

    mm/thp: Use pmdp_splitting_flush_notify to clear pmd on splitting
    
    Some arch may require an explicit IPI before a THP PMD split. This
    ensures that a local_irq_disable can prevent a parallel THP PMD split.
    So use new function which arch can override
    
    Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>

diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
index fe617b7e4be6..6a0b2ab899d1 100644
--- a/include/asm-generic/pgtable.h
+++ b/include/asm-generic/pgtable.h
@@ -184,6 +184,24 @@ static inline void pmdp_set_wrprotect(struct mm_struct *mm,
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */
 #endif
 
+#ifndef __HAVE_ARCH_PMDP_SPLITTING_FLUSH_NOTIFY
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+static inline void pmdp_splitting_flush_notify(struct vm_area_struct *vma,
+					       unsigned long address,
+					       pmd_t *pmdp)
+{
+	pmdp_clear_flush_notify(vma, address, pmdp);
+}
+#else
+static inline void pmdp_splitting_flush_notify(struct vm_area_struct *vma,
+					       unsigned long address,
+					       pmd_t *pmdp)
+{
+	BUG();
+}
+#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
+#endif
+
 #ifndef __HAVE_ARCH_PGTABLE_DEPOSIT
 extern void pgtable_trans_huge_deposit(struct mm_struct *mm, pmd_t *pmdp,
 				       pgtable_t pgtable);
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index cce4604c192f..81e9578bf43a 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2606,9 +2606,10 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
 
 	write = pmd_write(*pmd);
 	young = pmd_young(*pmd);
-
-	/* leave pmd empty until pte is filled */
-	pmdp_clear_flush_notify(vma, haddr, pmd);
+	/*
+	 * leave pmd empty until pte is filled.
+	 */
+	pmdp_splitting_flush_notify(vma, haddr, pmd);
 
 	pgtable = pgtable_trans_huge_withdraw(mm, pmd);
 	pmd_populate(mm, &_pmd, pgtable);

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