mm, THP, swap: make reuse_swap_page() works for THP swapped out

After supporting to delay THP (Transparent Huge Page) splitting after
swapped out, it is possible that some page table mappings of the THP are
turned into swap entries.  So reuse_swap_page() need to check the swap
count in addition to the map count as before.  This patch done that.

In the huge PMD write protect fault handler, in addition to the page map
count, the swap count need to be checked too, so the page lock need to
be acquired too when calling reuse_swap_page() in addition to the page
table lock.

[ying.huang@intel.com: silence a compiler warning]
Link: http://lkml.kernel.org/r/87bmnzizjy.fsf@yhuang-dev.intel.com
Link: http://lkml.kernel.org/r/20170724051840.2309-4-ying.huang@intel.com
Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Shaohua Li <shli@kernel.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Ross Zwisler <ross.zwisler@intel.com> [for brd.c, zram_drv.c, pmem.c]
Cc: Vishal L Verma <vishal.l.verma@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 964b4f1fba4a9cac38f556769549dade39fad4cf..7176ba780e83f3901e19a1578f604baf29b855be 100644 (file)
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -510,8 +510,8 @@ static inline int swp_swapcount(swp_entry_t entry)
        return 0;
 }
 
-#define reuse_swap_page(page, total_mapcount) \
-       (page_trans_huge_mapcount(page, total_mapcount) == 1)
+#define reuse_swap_page(page, total_map_swapcount) \
+       (page_trans_huge_mapcount(page, total_map_swapcount) == 1)
 
 static inline int try_to_free_swap(struct page *page)
 {

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 7f0b3f6db9238adf2efbf35db1e05f0bd087af12..02dfe635c9fe0285f10e285936bf0b7a515f72fd 100644 (file)
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1240,15 +1240,29 @@ int do_huge_pmd_wp_page(struct vm_fault *vmf, pmd_t orig_pmd)
         * We can only reuse the page if nobody else maps the huge page or it's
         * part.
         */
-       if (page_trans_huge_mapcount(page, NULL) == 1) {
+       if (!trylock_page(page)) {
+               get_page(page);
+               spin_unlock(vmf->ptl);
+               lock_page(page);
+               spin_lock(vmf->ptl);
+               if (unlikely(!pmd_same(*vmf->pmd, orig_pmd))) {
+                       unlock_page(page);
+                       put_page(page);
+                       goto out_unlock;
+               }
+               put_page(page);
+       }
+       if (reuse_swap_page(page, NULL)) {
                pmd_t entry;
                entry = pmd_mkyoung(orig_pmd);
                entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
                if (pmdp_set_access_flags(vma, haddr, vmf->pmd, entry,  1))
                        update_mmu_cache_pmd(vma, vmf->address, vmf->pmd);
                ret |= VM_FAULT_WRITE;
+               unlock_page(page);
                goto out_unlock;
        }
+       unlock_page(page);
        get_page(page);
        spin_unlock(vmf->ptl);
 alloc:

diff --git a/mm/memory.c b/mm/memory.c
index 1416485e278ceff9fc4817caa5fd36c3b5c8f037..3dd8bb46391bc014bd54417296c4c308962c131a 100644 (file)
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2619,7 +2619,7 @@ static int do_wp_page(struct vm_fault *vmf)
         * not dirty accountable.
         */
        if (PageAnon(vmf->page) && !PageKsm(vmf->page)) {
-               int total_mapcount;
+               int total_map_swapcount;
                if (!trylock_page(vmf->page)) {
                        get_page(vmf->page);
                        pte_unmap_unlock(vmf->pte, vmf->ptl);
@@ -2634,8 +2634,8 @@ static int do_wp_page(struct vm_fault *vmf)
                        }
                        put_page(vmf->page);
                }
-               if (reuse_swap_page(vmf->page, &total_mapcount)) {
-                       if (total_mapcount == 1) {
+               if (reuse_swap_page(vmf->page, &total_map_swapcount)) {
+                       if (total_map_swapcount == 1) {
                                /*
                                 * The page is all ours. Move it to
                                 * our anon_vma so the rmap code will

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 164d9624d7d20e8453d953ede6f9828e2d8203d2..2bfbfb87123a1f57fcd8448156389c19bdb59c36 100644 (file)
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1405,9 +1405,89 @@ static bool page_swapped(struct page *page)
                return swap_page_trans_huge_swapped(si, entry);
        return false;
 }
+
+static int page_trans_huge_map_swapcount(struct page *page, int *total_mapcount,
+                                        int *total_swapcount)
+{
+       int i, map_swapcount, _total_mapcount, _total_swapcount;
+       unsigned long offset = 0;
+       struct swap_info_struct *si;
+       struct swap_cluster_info *ci = NULL;
+       unsigned char *map = NULL;
+       int mapcount, swapcount = 0;
+
+       /* hugetlbfs shouldn't call it */
+       VM_BUG_ON_PAGE(PageHuge(page), page);
+
+       if (likely(!PageTransCompound(page))) {
+               mapcount = atomic_read(&page->_mapcount) + 1;
+               if (total_mapcount)
+                       *total_mapcount = mapcount;
+               if (PageSwapCache(page))
+                       swapcount = page_swapcount(page);
+               if (total_swapcount)
+                       *total_swapcount = swapcount;
+               return mapcount + swapcount;
+       }
+
+       page = compound_head(page);
+
+       _total_mapcount = _total_swapcount = map_swapcount = 0;
+       if (PageSwapCache(page)) {
+               swp_entry_t entry;
+
+               entry.val = page_private(page);
+               si = _swap_info_get(entry);
+               if (si) {
+                       map = si->swap_map;
+                       offset = swp_offset(entry);
+               }
+       }
+       if (map)
+               ci = lock_cluster(si, offset);
+       for (i = 0; i < HPAGE_PMD_NR; i++) {
+               mapcount = atomic_read(&page[i]._mapcount) + 1;
+               _total_mapcount += mapcount;
+               if (map) {
+                       swapcount = swap_count(map[offset + i]);
+                       _total_swapcount += swapcount;
+               }
+               map_swapcount = max(map_swapcount, mapcount + swapcount);
+       }
+       unlock_cluster(ci);
+       if (PageDoubleMap(page)) {
+               map_swapcount -= 1;
+               _total_mapcount -= HPAGE_PMD_NR;
+       }
+       mapcount = compound_mapcount(page);
+       map_swapcount += mapcount;
+       _total_mapcount += mapcount;
+       if (total_mapcount)
+               *total_mapcount = _total_mapcount;
+       if (total_swapcount)
+               *total_swapcount = _total_swapcount;
+
+       return map_swapcount;
+}
 #else
 #define swap_page_trans_huge_swapped(si, entry)        swap_swapcount(si, entry)
 #define page_swapped(page)                     (page_swapcount(page) != 0)
+
+static int page_trans_huge_map_swapcount(struct page *page, int *total_mapcount,
+                                        int *total_swapcount)
+{
+       int mapcount, swapcount = 0;
+
+       /* hugetlbfs shouldn't call it */
+       VM_BUG_ON_PAGE(PageHuge(page), page);
+
+       mapcount = page_trans_huge_mapcount(page, total_mapcount);
+       if (PageSwapCache(page))
+               swapcount = page_swapcount(page);
+       if (total_swapcount)
+               *total_swapcount = swapcount;
+       return mapcount + swapcount;
+}
 #endif
 
 /*
@@ -1416,23 +1496,27 @@ static bool page_swapped(struct page *page)
  * on disk will never be read, and seeking back there to write new content
  * later would only waste time away from clustering.
  *
- * NOTE: total_mapcount should not be relied upon by the caller if
+ * NOTE: total_map_swapcount should not be relied upon by the caller if
  * reuse_swap_page() returns false, but it may be always overwritten
  * (see the other implementation for CONFIG_SWAP=n).
  */
-bool reuse_swap_page(struct page *page, int *total_mapcount)
+bool reuse_swap_page(struct page *page, int *total_map_swapcount)
 {
-       int count;
+       int count, total_mapcount, total_swapcount;
 
        VM_BUG_ON_PAGE(!PageLocked(page), page);
        if (unlikely(PageKsm(page)))
                return false;
-       count = page_trans_huge_mapcount(page, total_mapcount);
-       if (count <= 1 && PageSwapCache(page)) {
-               count += page_swapcount(page);
-               if (count != 1)
-                       goto out;
+       count = page_trans_huge_map_swapcount(page, &total_mapcount,
+                                             &total_swapcount);
+       if (total_map_swapcount)
+               *total_map_swapcount = total_mapcount + total_swapcount;
+       if (count == 1 && PageSwapCache(page) &&
+           (likely(!PageTransCompound(page)) ||
+            /* The remaining swap count will be freed soon */
+            total_swapcount == page_swapcount(page))) {
                if (!PageWriteback(page)) {
+                       page = compound_head(page);
                        delete_from_swap_cache(page);
                        SetPageDirty(page);
                } else {
@@ -1448,7 +1532,7 @@ bool reuse_swap_page(struct page *page, int *total_mapcount)
                        spin_unlock(&p->lock);
                }
        }
-out:
+
        return count <= 1;
 }