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Commit e7a00c45 authored by Andrea Arcangeli's avatar Andrea Arcangeli Committed by Linus Torvalds
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thp: add pmd_huge_pte to mm_struct 



This increase the size of the mm struct a bit but it is needed to
preallocate one pte for each hugepage so that split_huge_page will not
require a fail path.  Guarantee of success is a fundamental property of
split_huge_page to avoid decrasing swapping reliability and to avoid
adding -ENOMEM fail paths that would otherwise force the hugepage-unaware
VM code to learn rolling back in the middle of its pte mangling operations
(if something we need it to learn handling pmd_trans_huge natively rather
being capable of rollback).  When split_huge_page runs a pte is needed to
succeed the split, to map the newly splitted regular pages with a regular
pte.  This way all existing VM code remains backwards compatible by just
adding a split_huge_page* one liner.  The memory waste of those
preallocated ptes is negligible and so it is worth it.

Signed-off-by: default avatarAndrea Arcangeli <aarcange@redhat.com>
Acked-by: default avatarRik van Riel <riel@redhat.com>
Acked-by: default avatarMel Gorman <mel@csn.ul.ie>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 4e6af67e

include/linux/mm_types.h

+3 −0
Original line number Original line Diff line number Diff line
@@ -309,6 +309,9 @@ struct mm_struct { 
#endif

#endif

#ifdef CONFIG_MMU_NOTIFIER

#ifdef CONFIG_MMU_NOTIFIER

	struct mmu_notifier_mm *mmu_notifier_mm;

	struct mmu_notifier_mm *mmu_notifier_mm;

#endif

#ifdef CONFIG_TRANSPARENT_HUGEPAGE

	pgtable_t pmd_huge_pte; /* protected by page_table_lock */

#endif

#endif

	/* How many tasks sharing this mm are OOM_DISABLE */

	/* How many tasks sharing this mm are OOM_DISABLE */

	atomic_t oom_disable_count;

	atomic_t oom_disable_count;

kernel/fork.c

+7 −0
Original line number Original line Diff line number Diff line
@@ -529,6 +529,9 @@ void __mmdrop(struct mm_struct *mm) 
	mm_free_pgd(mm);

	mm_free_pgd(mm);

	destroy_context(mm);

	destroy_context(mm);

	mmu_notifier_mm_destroy(mm);

	mmu_notifier_mm_destroy(mm);

#ifdef CONFIG_TRANSPARENT_HUGEPAGE

	VM_BUG_ON(mm->pmd_huge_pte);

#endif

	free_mm(mm);

	free_mm(mm);

}

}

EXPORT_SYMBOL_GPL(__mmdrop);

EXPORT_SYMBOL_GPL(__mmdrop);
@@ -669,6 +672,10 @@ struct mm_struct *dup_mm(struct task_struct *tsk) 
	mm->token_priority = 0;

	mm->token_priority = 0;

	mm->last_interval = 0;

	mm->last_interval = 0;





#ifdef CONFIG_TRANSPARENT_HUGEPAGE

	mm->pmd_huge_pte = NULL;

#endif



	if (!mm_init(mm, tsk))

	if (!mm_init(mm, tsk))

		goto fail_nomem;

		goto fail_nomem;