Messages in this thread | | | Date | Fri, 23 Jan 2015 17:58:02 +0200 | From | "Kirill A. Shutemov" <> | Subject | Re: [PATCH] mm: incorporate read-only pages into transparent huge pages |
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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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