shmem knows for sure that the page is in swap cache when attempting to
charge a page, because the cache charge entry function has a check for
it. Only anon pages may be removed from swap cache already when
trying to charge their swapin.
Adjust the comment, though: '4969c11 mm: fix swapin race condition'
added a stable PageSwapCache check under the page lock in the
do_swap_page() before calling the memory controller, so it's
unuse_pte()'s pte_same() that may fail.
Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxx>
---
mm/memcontrol.c | 22 ++++++++++++++--------
1 files changed, 14 insertions(+), 8 deletions(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 9433bff..ffd9323 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2819,14 +2819,6 @@ static int __mem_cgroup_try_charge_swapin(struct mm_struct *mm,
return 0;
if (!do_swap_account)
goto charge_cur_mm;
- /*
- * A racing thread's fault, or swapoff, may have already updated
- * the pte, and even removed page from swap cache: in those cases
- * do_swap_page()'s pte_same() test will fail; but there's also a
- * KSM case which does need to charge the page.
- */
- if (!PageSwapCache(page))
- goto charge_cur_mm;
memcg = try_get_mem_cgroup_from_page(page);
if (!memcg)
goto charge_cur_mm;
@@ -2849,6 +2841,20 @@ int mem_cgroup_try_charge_swapin(struct mm_struct *mm, struct page *page,
*memcgp = NULL;
if (mem_cgroup_disabled())
return 0;
+ /*
+ * A racing thread's fault, or swapoff, may have already
+ * updated the pte, and even removed page from swap cache: in
+ * those cases unuse_pte()'s pte_same() test will fail; but
+ * there's also a KSM case which does need to charge the page.
+ */
+ if (!PageSwapCache(page)) {
+ int ret;
+
+ ret = __mem_cgroup_try_charge(mm, gfp_mask, 1, memcgp, true);
+ if (ret == -EINTR)
+ ret = 0;
+ return ret;
+ }
return __mem_cgroup_try_charge_swapin(mm, page, gfp_mask, memcgp);
}
--
1.7.7.6
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