mm: cleanup "swapcache" in do_swap_page

I dislike the way in which "swapcache" gets used in do_swap_page():
there is always a page from swapcache there (even if maybe uncached by
the time we lock it), but tests are made according to "swapcache".
Rework that with "page != swapcache", as has been done in unuse_pte().

Signed-off-by: Hugh Dickins <hughd@google.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Petr Holasek <pholasek@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Izik Eidus <izik.eidus@ravellosystems.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 8 insertions, 10 deletions

diff --git a/mm/memory.c b/mm/memory.c
index ec8ba011fa7d..705473afc1f4 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2954,7 +2954,7 @@ static int do_swap_page(struct mm_struct *mm, struct vm_area_struct *vma,
                 unsigned int flags, pte_t orig_pte)
 {
         spinlock_t *ptl;
-        struct page *page, *swapcache = NULL;
+        struct page *page, *swapcache;
         swp_entry_t entry;
         pte_t pte;
         int locked;
@@ -3005,9 +3005,11 @@ static int do_swap_page(struct mm_struct *mm, struct vm_area_struct *vma,
                  */
                 ret = VM_FAULT_HWPOISON;
                 delayacct_clear_flag(DELAYACCT_PF_SWAPIN);
+                swapcache = page;
                 goto out_release;
         }
 
+        swapcache = page;
         locked = lock_page_or_retry(page, mm, flags);
 
         delayacct_clear_flag(DELAYACCT_PF_SWAPIN);
@@ -3025,16 +3027,12 @@ static int do_swap_page(struct mm_struct *mm, struct vm_area_struct *vma,
         if (unlikely(!PageSwapCache(page) || page_private(page) != entry.val))
                 goto out_page;
 
-        swapcache = page;
         page = ksm_might_need_to_copy(page, vma, address);
         if (unlikely(!page)) {
                 ret = VM_FAULT_OOM;
                 page = swapcache;
-                swapcache = NULL;
                 goto out_page;
         }
-        if (page == swapcache)
-                swapcache = NULL;
 
         if (mem_cgroup_try_charge_swapin(mm, page, GFP_KERNEL, &ptr)) {
                 ret = VM_FAULT_OOM;
@@ -3078,10 +3076,10 @@ static int do_swap_page(struct mm_struct *mm, struct vm_area_struct *vma,
         }
         flush_icache_page(vma, page);
         set_pte_at(mm, address, page_table, pte);
-        if (swapcache) /* ksm created a completely new copy */
-                page_add_new_anon_rmap(page, vma, address);
-        else
+        if (page == swapcache)
                 do_page_add_anon_rmap(page, vma, address, exclusive);
+        else /* ksm created a completely new copy */
+                page_add_new_anon_rmap(page, vma, address);
         /* It's better to call commit-charge after rmap is established */
         mem_cgroup_commit_charge_swapin(page, ptr);
 
@@ -3089,7 +3087,7 @@ static int do_swap_page(struct mm_struct *mm, struct vm_area_struct *vma,
         if (vm_swap_full() || (vma->vm_flags & VM_LOCKED) || PageMlocked(page))
                 try_to_free_swap(page);
         unlock_page(page);
-        if (swapcache) {
+        if (page != swapcache) {
                 /*
                  * Hold the lock to avoid the swap entry to be reused
                  * until we take the PT lock for the pte_same() check
@@ -3122,7 +3120,7 @@ out_page:
         unlock_page(page);
 out_release:
         page_cache_release(page);
-        if (swapcache) {
+        if (page != swapcache) {
                 unlock_page(swapcache);
                 page_cache_release(swapcache);
         }