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| author | Hugh Dickins <hughd@google.com> | 2016-09-24 05:27:04 +0200 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2016-09-24 20:20:01 +0200 |
| commit | b385d21f27d86426472f6ae92a231095f7de2a8d (patch) | |
| tree | a8e2a20246c8beaf70a429a1e66f07ad437320af /mm | |
| parent | huge tmpfs: fix Committed_AS leak (diff) | |
| download | linux-b385d21f27d86426472f6ae92a231095f7de2a8d.tar.xz linux-b385d21f27d86426472f6ae92a231095f7de2a8d.zip | |
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')
| -rw-r--r-- | mm/vmscan.c | 19 |
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: } } -#ifdef CONFIG_ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH -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; -} -#else -static inline void init_tlb_ubc(void) -{ -} -#endif /* CONFIG_ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH */ - /* * 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(); - blk_start_plug(&plug); while (nr[LRU_INACTIVE_ANON] || nr[LRU_ACTIVE_FILE] || nr[LRU_INACTIVE_FILE]) { |