Re: [PATCHv4 37/39] thp: handle write-protect exception tofile-backed huge pages

[Hillf Danton]

On Thu, May 23, 2013 at 8:08 PM, Kirill A. Shutemov
<kirill.shutemov@xxxxxxxxxxxxxxx> wrote:
> Hillf Danton wrote:
>> On Sun, May 12, 2013 at 9:23 AM, Kirill A. Shutemov
>> <kirill.shutemov@xxxxxxxxxxxxxxx> wrote:
>> > @@ -1120,7 +1119,7 @@ int do_huge_pmd_wp_page(struct mm_struct *mm, struct vm_area_struct *vma,
>> >
>> >         page = pmd_page(orig_pmd);
>> >         VM_BUG_ON(!PageCompound(page) || !PageHead(page));
>> > -       if (page_mapcount(page) == 1) {
>> > +       if (PageAnon(page) && page_mapcount(page) == 1) {
>>
>> Could we avoid copying huge page if
>> no-one else is using it, no matter anon?
>
> No. The page is still in page cache and can be later accessed later.
> We could isolate the page from page cache, but I'm not sure whether it's
> good idea.
>
Hugetlb tries to avoid copying pahe.

	/* If no-one else is actually using this page, avoid the copy
	 * and just make the page writable */
	avoidcopy = (page_mapcount(old_page) == 1);
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