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

Byungchul Park
2024-05-27T04:25:54Z

On Mon, May 27, 2024 at 01:19:46PM +0900, Byungchul Park wrote:
> On Mon, May 27, 2024 at 12:46:14PM +0900, Byungchul Park wrote:
> > On Sun, May 26, 2024 at 07:43:10PM -0700, Dave Hansen wrote:
> > > On 5/26/24 18:57, Byungchul Park wrote:
> > > ...
> > > > Plus, I will add another give-up at code changing the permission of vma
> > > > to writable.
> > >
> > > I suspect you have a much more general problem on your hands. Just
> > > tweaking the VFS or mmap() code likely isn't going to cut it.
>
> What a stupid idiot I am.
>
> I already discuss the exact cases with Nadav Amit at the very beginning
> around v1. I didn't remember it when I was answering to you.
>
> mmap() or changing the permission by user already performs TLB flush
> needed within that code, which LUF never touch.
>
> Worth noting currently LUF touchs only unmapping during migration or
> reclaim. Other updating mapping would perform TLB flush it needs, as is.
> I guess updating page cache is also already perform TLB flush needed.

This may not be the case tho.. I might need to work on page cache.

Byungchul

> I need to check it. Probably, it would already do.
>
> Byungchul
>
> > LUF is interested in limited folios that are migratable or reclaimable
> > in lru for now. So, IMHO, fixing a few things is going to cut it.
> >
> > > I guess we'll see what you come up with next, but this email was really
> > > just the result of Vlastimil and I chatting on IRC for five minutes
> > > about this set.
> > >
> > > It has absolutely not been tested nor reviewed enough. <fud>I hope the
> > > performance gains stick around once more of the bugs are gone.</fud>
> >
> > Sure. It should be.
> >
> > Byungchul