On Fri, Jan 23, 2015 at 09:57:03AM -0500, Rik van Riel wrote:
> On 01/23/2015 06:37 AM, Kirill A. Shutemov wrote:
> > On Fri, Jan 23, 2015 at 09:47:36AM +0200, Ebru Akagunduz wrote:
> >> This patch aims to improve THP collapse rates, by allowing
> >> THP collapse in the presence of read-only ptes, like those
> >> left in place by do_swap_page after a read fault.
> >>
> >> Currently THP can collapse 4kB pages into a THP when
> >> there are up to khugepaged_max_ptes_none pte_none ptes
> >> in a 2MB range. This patch applies the same limit for
> >> read-only ptes.
>
> >> @@ -2179,6 +2179,17 @@ static int __collapse_huge_page_isolate(struct
> >> vm_area_struct *vma,
> >> */
> >> if (!trylock_page(page))
> >> goto out;
> >> + if (!pte_write(pteval)) {
> >> + if (PageSwapCache(page) && !reuse_swap_page(page)) {
> >> + unlock_page(page);
> >> + goto out;
> >> + }
> >> + /*
> >> + * Page is not in the swap cache, and page count is
> >> + * one (see above). It can be collapsed into a THP.
> >> + */
> >> + }
> >
> > Hm. As a side effect it will effectevely allow collapse in PROT_READ vmas,
> > right? I'm not convinced it's a good idea.
>
> It will only allow a THP collapse if there is at least one
> read-write pte.
>
> I suspect that excludes read-only VMAs automatically.
Ah. Okay. I missed that condition.
Looks good to me.
--
Kirill A. Shutemov
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