From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
The page walker functions are only called _via_ the page
walker. I don't see this changing any time soon. The
page walker only calls walk->hugetlb_entry() under an
#ifdef CONFIG_HUGETLB_PAGE.
With this in place, I think putting BUG()s in the
->hugetlb_entry handlers is a bit like wearing a belt and
suspenders.
This axes the BUG() from the mincore ->hugetlb_entry along
with the #ifdef. The compiler is more than smart enough
to do the right thing when it sees:
if (1)
return;
// unreachable
The only downside here is that we now need some header stubs
for huge_pte_none() / huge_pte_get().
Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
---
b/include/linux/hugetlb.h | 10 ++++++++++
b/mm/mincore.c | 9 +++++----
2 files changed, 15 insertions(+), 4 deletions(-)
diff -puN include/linux/hugetlb.h~cleanup-hugetlbfs-mincore-1 include/linux/hugetlb.h
--- a/include/linux/hugetlb.h~cleanup-hugetlbfs-mincore-1 2014-06-02 14:20:20.144845525 -0700
+++ b/include/linux/hugetlb.h 2014-06-02 14:20:20.149845750 -0700
@@ -458,6 +458,16 @@ static inline spinlock_t *huge_pte_lockp
{
return &mm->page_table_lock;
}
+static inline int huge_pte_none(pte_t pte)
+{
+ WARN_ONCE(1, "%s() called when hugetlbfs disabled", __func__);
+ return 1;
+}
+static inline pte_t huge_ptep_get(pte_t *pte)
+{
+ WARN_ONCE(1, "%s() called when hugetlbfs disabled", __func__);
+ return __pte(0);
+}
#endif /* CONFIG_HUGETLB_PAGE */
static inline spinlock_t *huge_pte_lock(struct hstate *h,
diff -puN mm/mincore.c~cleanup-hugetlbfs-mincore-1 mm/mincore.c
--- a/mm/mincore.c~cleanup-hugetlbfs-mincore-1 2014-06-02 14:20:20.146845615 -0700
+++ b/mm/mincore.c 2014-06-02 14:20:20.149845750 -0700
@@ -23,8 +23,12 @@ static int mincore_hugetlb_page_range(pt
unsigned long addr, unsigned long end,
struct mm_walk *walk)
{
-#ifdef CONFIG_HUGETLB_PAGE
unsigned char *vec = walk->private;
+
+ /* This is as good as an explicit ifdef */
+ if (!is_vm_hugetlb_page(walk->vma))
+ return 0;
+
while (1) {
int present = !huge_pte_none(huge_ptep_get(ptep));
while (1) {
@@ -38,9 +42,6 @@ static int mincore_hugetlb_page_range(pt
break;
}
}
-#else
- BUG();
-#endif
return 0;
}
_
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