projects/linux·commit e7a00c45

thp: add pmd_huge_pte to mm_struct

e7a00c45 · Andrea Arcangeli <[email protected]> · 2011-01-13 15:46:45 -08:00

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 <[email protected]>
Acked-by: Rik van Riel <[email protected]>
Acked-by: Mel Gorman <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
Commit
e7a00c45f29c0155007aa150bf231a70fa470365
Parents
4e6af67e

Changes

2 files changed · +10 −0

FileStatusAddDelContent
include/linux/mm_types.hmodified+3−0View file
kernel/fork.cmodified+7−0View file

include/linux/mm_types.h

View file
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index bb7288a..26bc4e2 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -310,6 +310,9 @@ struct mm_struct {
#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

View file
diff --git a/kernel/fork.c b/kernel/fork.c
index 1499607..f78f50b 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;