mm: add three more cond_resched() in swapoff

Add a cond_resched() in the unuse_pmd_range() loop (so as to call it
even when pmd none or trans_huge, like zap_pmd_range() does); and in the
unuse_mm() loop (since that might skip over many vmas).  shmem_unuse()
and radix_tree_locate_item() look good enough already.

Those were the obvious places, but in fact the stalls came from
find_next_to_unuse(), which sometimes scans through many unused entries.
Apply scan_swap_map()'s LATENCY_LIMIT of 256 there too; and only go off
to test frontswap_map when a used entry is found.

Link: http://lkml.kernel.org/r/alpine.LSU.2.11.1612052155140.13021@eggly.anvils
Signed-off-by: Hugh Dickins <hughd@google.com>
Reported-by: Eric Dumazet <edumazet@google.com>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 6 insertions, 7 deletions

diff --git a/mm/swapfile.c b/mm/swapfile.c
index f30438970cd1..1c6e0321205d 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1234,6 +1234,7 @@ static inline int unuse_pmd_range(struct vm_area_struct *vma, pud_t *pud,
 
         pmd = pmd_offset(pud, addr);
         do {
+                cond_resched();
                 next = pmd_addr_end(addr, end);
                 if (pmd_none_or_trans_huge_or_clear_bad(pmd))
                         continue;
@@ -1313,6 +1314,7 @@ static int unuse_mm(struct mm_struct *mm,
         for (vma = mm->mmap; vma; vma = vma->vm_next) {
                 if (vma->anon_vma && (ret = unuse_vma(vma, entry, page)))
                         break;
+                cond_resched();
         }
         up_read(&mm->mmap_sem);
         return (ret < 0)? ret: 0;
@@ -1350,15 +1352,12 @@ static unsigned int find_next_to_unuse(struct swap_info_struct *si,
                         prev = 0;
                         i = 1;
                 }
-                if (frontswap) {
-                        if (frontswap_test(si, i))
-                                break;
-                        else
-                                continue;
-                }
                 count = READ_ONCE(si->swap_map[i]);
                 if (count && swap_count(count) != SWAP_MAP_BAD)
-                        break;
+                        if (!frontswap || frontswap_test(si, i))
+                                break;
+                if ((i % LATENCY_LIMIT) == 0)
+                        cond_resched();
         }
         return i;
 }