Commit e7a00c45 authored Jan 13, 2011 by Andrea Arcangeli Committed by Linus Torvalds Jan 13, 2011

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: Andrea Arcangeli <aarcange@redhat.com>
Acked-by: Rik van Riel <riel@redhat.com>
Acked-by: Mel Gorman <mel@csn.ul.ie>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 4e6af67e

include/linux/mm_types.h

+3 −0

Original line number	Diff line number	Diff line
		@@ -309,6 +309,9 @@ struct mm_struct {
		#endif
		#ifdef CONFIG_MMU_NOTIFIER
		struct mmu_notifier_mm *mmu_notifier_mm;
		#endif
		#ifdef CONFIG_TRANSPARENT_HUGEPAGE
		pgtable_t pmd_huge_pte; /* protected by page_table_lock */
		#endif
		/* How many tasks sharing this mm are OOM_DISABLE */
		atomic_t oom_disable_count;

kernel/fork.c

+7 −0

Original line number	Diff line number	Diff line
		@@ -529,6 +529,9 @@ void __mmdrop(struct mm_struct *mm)
		mm_free_pgd(mm);
		destroy_context(mm);
		mmu_notifier_mm_destroy(mm);
		#ifdef CONFIG_TRANSPARENT_HUGEPAGE
		VM_BUG_ON(mm->pmd_huge_pte);
		#endif
		free_mm(mm);
		}
		EXPORT_SYMBOL_GPL(__mmdrop);
		@@ -669,6 +672,10 @@ struct mm_struct dup_mm(struct task_struct tsk)
		mm->token_priority = 0;
		mm->last_interval = 0;

		#ifdef CONFIG_TRANSPARENT_HUGEPAGE
		mm->pmd_huge_pte = NULL;
		#endif

		if (!mm_init(mm, tsk))
		goto fail_nomem;

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