Re: [PATCHv9 30/36] thp: add option to setup migration entiries during PMD split

["Kirill A. Shutemov" <kirill@shutemov.name>]

On Fri, Jul 31, 2015 at 05:09:38PM +0200, Jerome Marchand wrote:
> On 07/20/2015 04:21 PM, Kirill A. Shutemov wrote:
> > We are going to use migration PTE entires to stabilize page counts.
> > If the page is mapped with PMDs we need to split the PMD and setup
> > migration enties. It's reasonable to combine these operations to avoid
> > double-scanning over the page table.
> 
> Entries? Three different typos for three occurrences of the same word.
> You don't like it, do you?

Urgh..

>From 6c5b35ffcc425bcfc91b56d1ee404ab83cc667cf Mon Sep 17 00:00:00 2001
From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Date: Fri, 10 Apr 2015 12:39:14 +0300
Subject: [PATCH] thp: add option to setup migration entries during PMD split

We are going to use migration PTE entries to stabilize page counts.
If the page is mapped with PMDs we need to split the PMD and setup
migration entries. It's reasonable to combine these operations to avoid
double-scanning over the page table.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Tested-by: Sasha Levin <sasha.levin@oracle.com>
Tested-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Jerome Marchand <jmarchan@redhat.com>
---
 mm/huge_memory.c | 23 +++++++++++++++--------
 1 file changed, 15 insertions(+), 8 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 1e0e02786241..0d817863a739 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -25,6 +25,7 @@
 #include <linux/migrate.h>
 #include <linux/hashtable.h>
 #include <linux/userfaultfd_k.h>
+#include <linux/swapops.h>
 
 #include <asm/tlb.h>
 #include <asm/pgalloc.h>
@@ -2627,7 +2628,7 @@ static void __split_huge_zero_page_pmd(struct vm_area_struct *vma,
 }
 
 static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
-               unsigned long haddr)
+               unsigned long haddr, bool freeze)
 {
        struct mm_struct *mm = vma->vm_mm;
        struct page *page;
@@ -2669,12 +2670,18 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
                 * transferred to avoid any possibility of altering
                 * permissions across VMAs.
                 */
-               entry = mk_pte(page + i, vma->vm_page_prot);
-               entry = maybe_mkwrite(pte_mkdirty(entry), vma);
-               if (!write)
-                       entry = pte_wrprotect(entry);
-               if (!young)
-                       entry = pte_mkold(entry);
+               if (freeze) {
+                       swp_entry_t swp_entry;
+                       swp_entry = make_migration_entry(page + i, write);
+                       entry = swp_entry_to_pte(swp_entry);
+               } else {
+                       entry = mk_pte(page + i, vma->vm_page_prot);
+                       entry = maybe_mkwrite(pte_mkdirty(entry), vma);
+                       if (!write)
+                               entry = pte_wrprotect(entry);
+                       if (!young)
+                               entry = pte_mkold(entry);
+               }
                pte = pte_offset_map(&_pmd, haddr);
                BUG_ON(!pte_none(*pte));
                set_pte_at(mm, haddr, pte, entry);
@@ -2715,7 +2722,7 @@ void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd,
        mmu_notifier_invalidate_range_start(mm, haddr, haddr + HPAGE_PMD_SIZE);
        ptl = pmd_lock(mm, pmd);
        if (likely(pmd_trans_huge(*pmd)))
-               __split_huge_pmd_locked(vma, pmd, haddr);
+               __split_huge_pmd_locked(vma, pmd, haddr, false);
        spin_unlock(ptl);
        mmu_notifier_invalidate_range_end(mm, haddr, haddr + HPAGE_PMD_SIZE);
 }
-- 
 Kirill A. Shutemov