mm: thp: introduce separate TTU flag for thp freezing

TTU_MIGRATION is used to convert pte into migration entry until thp
split completes.  This behavior conflicts with thp migration added later
patches, so let's introduce a new TTU flag specifically for freezing.

try_to_unmap() is used both for thp split (via freeze_page()) and page
migration (via __unmap_and_move()).  In freeze_page(), ttu_flag given
for head page is like below (assuming anonymous thp):

    (TTU_IGNORE_MLOCK | TTU_IGNORE_ACCESS | TTU_RMAP_LOCKED | \
     TTU_MIGRATION | TTU_SPLIT_HUGE_PMD)

and ttu_flag given for tail pages is:

    (TTU_IGNORE_MLOCK | TTU_IGNORE_ACCESS | TTU_RMAP_LOCKED | \
     TTU_MIGRATION)

__unmap_and_move() calls try_to_unmap() with ttu_flag:

    (TTU_MIGRATION | TTU_IGNORE_MLOCK | TTU_IGNORE_ACCESS)

Now I'm trying to insert a branch for thp migration at the top of
try_to_unmap_one() like below

static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
                       unsigned long address, void *arg)
  {
          ...
          /* PMD-mapped THP migration entry */
          if (!pvmw.pte && (flags & TTU_MIGRATION)) {
              if (!PageAnon(page))
                  continue;

              set_pmd_migration_entry(&pvmw, page);
              continue;
          }
	  ...
  }

so try_to_unmap() for tail pages called by thp split can go into thp
migration code path (which converts *pmd* into migration entry), while
the expectation is to freeze thp (which converts *pte* into migration
entry.)

I detected this failure as a "bad page state" error in a testcase where
split_huge_page() is called from queue_pages_pte_range().

Link: http://lkml.kernel.org/r/20170717193955.20207-4-zi.yan@sent.com
Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Signed-off-by: Zi Yan <zi.yan@cs.rutgers.edu>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Anshuman Khandual <khandual@linux.vnet.ibm.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: David Nellans <dnellans@nvidia.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 43ef2c30cb0f59f83c05d23eea4a8aad87edefd1..f8ca2e74b81961f8cf38e48791c0733a64cee202 100644 (file)
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -93,8 +93,9 @@ enum ttu_flags {
        TTU_BATCH_FLUSH         = 0x40, /* Batch TLB flushes where possible
                                         * and caller guarantees they will
                                         * do a final flush if necessary */
-       TTU_RMAP_LOCKED         = 0x80  /* do not grab rmap lock:
+       TTU_RMAP_LOCKED         = 0x80, /* do not grab rmap lock:
                                         * caller holds it */
+       TTU_SPLIT_FREEZE        = 0x100,                /* freeze pte under splitting thp */
 };
 
 #ifdef CONFIG_MMU

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 0b51e70e0a8b5918e4de281a7d379eb4ce8c4323..8a97833ef0f1db8ec23c3b832f054ba622d4cc1d 100644 (file)
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2210,7 +2210,7 @@ static void freeze_page(struct page *page)
        VM_BUG_ON_PAGE(!PageHead(page), page);
 
        if (PageAnon(page))
-               ttu_flags |= TTU_MIGRATION;
+               ttu_flags |= TTU_SPLIT_FREEZE;
 
        unmap_success = try_to_unmap(page, ttu_flags);
        VM_BUG_ON_PAGE(!unmap_success, page);

diff --git a/mm/rmap.c b/mm/rmap.c
index c570f82e6827153316465b9e18f0fca376a1c1a1..5b26af8a7a29ad225993ee7803b2e2a6b8fd8420 100644 (file)
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1348,7 +1348,7 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
 
        if (flags & TTU_SPLIT_HUGE_PMD) {
                split_huge_pmd_address(vma, address,
-                               flags & TTU_MIGRATION, page);
+                               flags & TTU_SPLIT_FREEZE, page);
        }
 
        /*
@@ -1445,7 +1445,7 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
                         */
                        dec_mm_counter(mm, mm_counter(page));
                } else if (IS_ENABLED(CONFIG_MIGRATION) &&
-                               (flags & TTU_MIGRATION)) {
+                               (flags & (TTU_MIGRATION|TTU_SPLIT_FREEZE))) {
                        swp_entry_t entry;
                        pte_t swp_pte;
                        /*
@@ -1575,7 +1575,8 @@ bool try_to_unmap(struct page *page, enum ttu_flags flags)
         * locking requirements of exec(), migration skips
         * temporary VMAs until after exec() completes.
         */
-       if ((flags & TTU_MIGRATION) && !PageKsm(page) && PageAnon(page))
+       if ((flags & (TTU_MIGRATION|TTU_SPLIT_FREEZE))
+           && !PageKsm(page) && PageAnon(page))
                rwc.invalid_vma = invalid_migration_vma;
 
        if (flags & TTU_RMAP_LOCKED)