On Thu, Sep 22, 2016 at 10:41:50AM -0700, Hugh Dickins wrote: > 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 <hu...@google.com> > Cc: sta...@vger.kernel.org # 4.3+
Acked-by: Mel Gorman <mgor...@techsingularity.net> -- Mel Gorman SUSE Labs