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SubjectRe: [PATCH] mm: hugetlb: bail out unmapping after serving reference page
From
On Thu, Feb 23, 2012 at 5:06 AM, Andrew Morton
<akpm@linux-foundation.org> wrote:
>
> Perhaps add a little comment to this explaining what's going on?
>
>
> It would be sufficient to do
>
>        if (ref_page)
>                break;
>
> This is more efficient, and doesn't make people worry about whether
> this value of `page' is the same as the one which
> pte_page(huge_ptep_get()) earlier returned.
>
Hi Andrew

It is re-prepared,

===cut here===
From: Hillf Danton <dhillf@gmail.com>
Subject: [PATCH] mm: hugetlb: bail out unmapping after serving reference page

When unmapping given VM range, we could bail out if a reference page is
supplied and is unmapped, which is a minor optimization.

Signed-off-by: Hillf Danton <dhillf@gmail.com>
---

--- a/mm/hugetlb.c Wed Feb 22 19:34:12 2012
+++ b/mm/hugetlb.c Thu Feb 23 20:13:06 2012
@@ -2280,6 +2280,10 @@ void __unmap_hugepage_range(struct vm_ar
if (pte_dirty(pte))
set_page_dirty(page);
list_add(&page->lru, &page_list);
+
+ /* Bail out after unmapping reference page if supplied */
+ if (ref_page)
+ break;
}
spin_unlock(&mm->page_table_lock);
flush_tlb_range(vma, start, end);
--

> Why do we evaluate `page' twice inside that loop anyway?  And why do we
> check for huge_pte_none() twice?  It looks all messed up.
>

and a follow-up cleanup also attached.

Thanks
Hillf

===cut here===
From: Hillf Danton <dhillf@gmail.com>
Subject: [PATCH] mm: hugetlb: cleanup duplicated code in unmapping vm range

When unmapping given VM range, a couple of code duplicate, such as pte_page()
and huge_pte_none(), so a cleanup needed to compact them together.

Signed-off-by: Hillf Danton <dhillf@gmail.com>
---
--- a/mm/hugetlb.c Thu Feb 23 20:13:06 2012
+++ b/mm/hugetlb.c Thu Feb 23 20:30:16 2012
@@ -2245,16 +2245,23 @@ void __unmap_hugepage_range(struct vm_ar
if (huge_pmd_unshare(mm, &address, ptep))
continue;

+ pte = huge_ptep_get(ptep);
+ if (huge_pte_none(pte))
+ continue;
+
+ /*
+ * HWPoisoned hugepage is already unmapped and dropped reference
+ */
+ if (unlikely(is_hugetlb_entry_hwpoisoned(pte)))
+ continue;
+
+ page = pte_page(pte);
/*
* If a reference page is supplied, it is because a specific
* page is being unmapped, not a range. Ensure the page we
* are about to unmap is the actual page of interest.
*/
if (ref_page) {
- pte = huge_ptep_get(ptep);
- if (huge_pte_none(pte))
- continue;
- page = pte_page(pte);
if (page != ref_page)
continue;

@@ -2267,16 +2274,6 @@ void __unmap_hugepage_range(struct vm_ar
}

pte = huge_ptep_get_and_clear(mm, address, ptep);
- if (huge_pte_none(pte))
- continue;
-
- /*
- * HWPoisoned hugepage is already unmapped and dropped reference
- */
- if (unlikely(is_hugetlb_entry_hwpoisoned(pte)))
- continue;
-
- page = pte_page(pte);
if (pte_dirty(pte))
set_page_dirty(page);
list_add(&page->lru, &page_list);
--
--
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