Re: [PATCH v10 00/12] LUF(Lazy Unmap Flush) reducing tlb numbers over 90%

Byungchul Park
2024-05-31T02:07:01Z

On Thu, May 30, 2024 at 06:50:48AM -0700, Dave Hansen wrote:
> On 5/30/24 01:41, Byungchul Park wrote:
> > LUF should not optimize tlb flushes for mappings that users explicitly
> > change e.g. through mmap() and munmap().
>
> We are thoroughly going around in circles at this point.
>
> I'm not quite sure what to do. Ying and I see a problem that we've
> tried to explain a couple of times. We've tried to show the connection
> between a LUF-elided TLB flush and how that could affect a later
> munmap() or mmap(MAP_FIXED).
>
> But these responses seem to keep going back to the fact that LUF doesn't

I just wanted to understand exactly what Ying meant. My answer might be
done in a wrong way if I wrongly got him.

> directly affect munmap(), which is true, but quite irrelevant to the
> problem being described.
>
> So we're at an impasse.
>
> Byungchul, perhaps you should spin another series and maybe Ying and I

I don't think the current implementation is perfect. I just wanted to
know what I'm missing now but.. yes. It would be much better to
communicate with a real bug if existing.

I will respin the next version shortly.

Byungchul

> have to write up a test case to show the bug that we see. Or perhaps
> someone else can jump into the thread and bridge the communication gap.