Messages in this thread | | | Date | Mon, 13 May 2019 13:27:12 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH] mm: mmu_gather: remove __tlb_reset_range() for force flush |
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On Mon, May 13, 2019 at 09:21:01AM +0000, Nadav Amit wrote: > > On May 13, 2019, at 2:12 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> >> The other thing I was thinking of is trying to detect overlap through > >> the page-tables themselves, but we have a distinct lack of storage > >> there. > > > > We might just use some state in the pmd, there's still 2 _pt_pad_[12] in > > struct page to 'use'. So we could come up with some tlb generation > > scheme that would detect conflict. > > It is rather easy to come up with a scheme (and I did similar things) if you > flush the table while you hold the page-tables lock. But if you batch across > page-tables it becomes harder.
Yeah; finding that out now. I keep finding holes :/
> Thinking about it while typing, perhaps it is simpler than I think - if you > need to flush range that runs across more than a single table, you are very > likely to flush a range of more than 33 entries, so anyhow you are likely to > do a full TLB flush.
We can't rely on the 33, that x86 specific. Other architectures can have another (or no) limit on that.
> So perhaps just avoiding the batching if only entries from a single table > are flushed would be enough.
That's near to what Will suggested initially, just flush the entire thing when there's a conflict.
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