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Date: Mon, 27 May 2024 13:25:48 +0900
From: Byungchul Park <byungchul@sk.com>
To: Dave Hansen <dave.hansen@intel.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	kernel_team@skhynix.com, akpm@linux-foundation.org,
	ying.huang@intel.com, vernhao@tencent.com,
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	david@redhat.com, peterz@infradead.org, luto@kernel.org,
	tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
	dave.hansen@linux.intel.com, rjgolo@gmail.com
Subject: Re: [PATCH v10 00/12] LUF(Lazy Unmap Flush) reducing tlb numbers
 over 90%
Message-ID: <20240527042548.GD12937@system.software.com>
References: <20240510065206.76078-1-byungchul@sk.com>
 <982317c0-7faa-45f0-82a1-29978c3c9f4d@intel.com>
 <20240527015732.GA61604@system.software.com>
 <a28df276-069c-4d4d-abaf-efc24983211e@intel.com>
 <20240527034614.GA12937@system.software.com>
 <20240527041946.GC12937@system.software.com>
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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