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authorAndrea Arcangeli <aarcange@redhat.com>2011-01-13 15:46:45 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2011-01-13 17:32:41 -0800
commite7a00c45f29c0155007aa150bf231a70fa470365 (patch)
tree3225a79905dede614ed44e98776cdc6285bbd28a /kernel
parent4e6af67e970a2ac287739a4c526c857b5bda27ec (diff)
downloadlinux-linaro-precise-e7a00c45f29c0155007aa150bf231a70fa470365.tar.gz
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>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/fork.c7
1 files changed, 7 insertions, 0 deletions
diff --git a/kernel/fork.c b/kernel/fork.c
index 1499607e4da..f78f50ba6cb 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -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;