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>

diff --git a/mm/memory.c b/mm/memory.c
index ec8ba011fa7dd3397a3ba629b40082eabf6c45d3..705473afc1f4f6c32eeaa1726e04068993dd946e 100644 (file)
--- 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);
        }