linux-kernel - Re: [RFC PATCH v12 00/26] LUF(Lazy Unmap Flush) reducing tlb numbers over 90%

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Message-ID: <6cdstauw4b64gpi6xxmuumuzvkgtjpczienh7neogqjlarqilv@eujvenmk2uyh>
Date: Fri, 21 Feb 2025 17:14:51 -0800
From: Shakeel Butt <shakeel.butt@...ux.dev>
To: Vlastimil Babka <vbabka@...e.cz>, sj@...nel.org
Cc: Dave Hansen <dave.hansen@...el.com>, Byungchul Park <byungchul@...com>, 
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, kernel_team@...ynix.com, 
	akpm@...ux-foundation.org, ying.huang@...el.com, vernhao@...cent.com, 
	mgorman@...hsingularity.net, hughd@...gle.com, willy@...radead.org, david@...hat.com, 
	peterz@...radead.org, luto@...nel.org, tglx@...utronix.de, mingo@...hat.com, 
	bp@...en8.de, dave.hansen@...ux.intel.com, rjgolo@...il.com
Subject: Re: [RFC PATCH v12 00/26] LUF(Lazy Unmap Flush) reducing tlb numbers
 over 90%

On Thu, Feb 20, 2025 at 04:29:51PM +0100, Vlastimil Babka wrote:
> On 2/20/25 16:15, Dave Hansen wrote:
> > On 2/19/25 21:20, Byungchul Park wrote:
> >> I'm posting the latest version so that anyone can try luf mechanism if
> >> wanted by any chance.  However, I tagged RFC again because there are
> >> still issues that should be resolved to merge to mainline:
> > 
> > I don't see anything fundamentally different here from the last 11
> > versions. I think the entire approach is dangerous and basically makes
> > things impossible to debug. It's not clear that some of the failure
> > scenarios that I've brought up in the past have actually been fixed.
> 
> Yes, and it's still an invasive change to the buddy allocator.
> IIRC at Plumbers the opinion in the audience was that there might be ways to
> improve the batching on unmap to reduce the flushes without such an invasive
> and potentially dangerous change? Has that been investigated?
> 

I know SJ (CCed) is working on making TLB flush batching work for
process_madvise().