path: root/mm
diff options
authorHugh Dickins <hughd@google.com>2016-09-23 20:27:04 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2016-09-24 11:20:01 -0700
commitb385d21f27d86426472f6ae92a231095f7de2a8d (patch)
treea8e2a20246c8beaf70a429a1e66f07ad437320af /mm
parent71664665c3e3ca5ff61ef5fc65480f82cd575eb2 (diff)
mm: delete unnecessary and unsafe init_tlb_ubc()
init_tlb_ubc() looked unnecessary to me: tlb_ubc is statically initialized with zeroes in the init_task, and copied from parent to child while it is quiescent in arch_dup_task_struct(); so I went to delete it. But inserted temporary debug WARN_ONs in place of init_tlb_ubc() to check that it was always empty at that point, and found them firing: because memcg reclaim can recurse into global reclaim (when allocating biosets for swapout in my case), and arrive back at the init_tlb_ubc() in shrink_node_memcg(). Resetting tlb_ubc.flush_required at that point is wrong: if the upper level needs a deferred TLB flush, but the lower level turns out not to, we miss a TLB flush. But fortunately, that's the only part of the protocol that does not nest: with the initialization removed, cpumask collects bits from upper and lower levels, and flushes TLB when needed. Fixes: 72b252aed506 ("mm: send one IPI per CPU to TLB flush all entries after unmapping pages") Signed-off-by: Hugh Dickins <hughd@google.com> Acked-by: Mel Gorman <mgorman@techsingularity.net> Cc: stable@vger.kernel.org # 4.3+ Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
1 files changed, 0 insertions, 19 deletions
diff --git a/mm/vmscan.c b/mm/vmscan.c
index b1e12a1ea9cf..0fe8b7113868 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2303,23 +2303,6 @@ out:
-static void init_tlb_ubc(void)
- /*
- * This deliberately does not clear the cpumask as it's expensive
- * and unnecessary. If there happens to be data in there then the
- * first SWAP_CLUSTER_MAX pages will send an unnecessary IPI and
- * then will be cleared.
- */
- current->tlb_ubc.flush_required = false;
-static inline void init_tlb_ubc(void)
* This is a basic per-node page freer. Used by both kswapd and direct reclaim.
@@ -2355,8 +2338,6 @@ static void shrink_node_memcg(struct pglist_data *pgdat, struct mem_cgroup *memc
scan_adjusted = (global_reclaim(sc) && !current_is_kswapd() &&
sc->priority == DEF_PRIORITY);
- init_tlb_ubc();