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From: Pedro Demarchi Gomes <pedrodemargomes@gmail.com>
To: Kiryl Shutsemau <kirill@shutemov.name>
Cc: Lance Yang <lance.yang@linux.dev>,
	david@kernel.org,  baolin.wang@linux.alibaba.com,
	akpm@linux-foundation.org, ljs@kernel.org, ziy@nvidia.com,
	 liam@infradead.org, nico.pache@linux.dev, ryan.roberts@arm.com,
	dev.jain@arm.com,  baohua@kernel.org, usama.arif@linux.dev,
	linux-mm@kvack.org,  linux-kernel@vger.kernel.org
Subject: Re: [PATCH mm-stable] mm/khugepaged: avoid unnecessary checking for swap entries when collapsing a mTHP
Date: Mon, 31 Aug 2026 15:53:34 -0300	[thread overview]
Message-ID: <apXHC7uYXE99ZgPp@fedora> (raw)
In-Reply-To: <apBB01VBbmV28gWP@thinkstation>

On Thu, Aug 27, 2026 at 03:07:10PM +0100, Kiryl Shutsemau wrote:
> On Thu, Aug 27, 2026 at 08:11:51PM +0800, Lance Yang wrote:
> > For the candidate above, the loop only reads its PTEs and returns
> > SCAN_SUCCEED. Pedro's bitmap lets mthp_collapse() determine that upfront
> > and skip the walk.
> > 
> > Emm ... as I asked before[1], any numbers showing how much the extra scan
> > costs?
> 
> With the win being only some scan cost, I don't think it is going to be
> measurable.
> 
> It can open a path to future work. For example, we could find fully
> populated mTHP windows in a PMD that is not eligible for collapse
> because unmapped > max_ptes_swap. Right now we just give up on the whole
> PMD in such cases.
> 
> But there are more wins to gain there. Just saying :P

Hi Kiryl,

I devised a patch based on your proposed future work idea. If you think it
makes sense, I can send it to the mailing list with a Suggested-by: tag.

Thanks!


  reply	other threads:[~2026-08-31 18:55 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2026-08-25 19:24 Pedro Demarchi Gomes
2026-08-26  4:43 ` Lance Yang
2026-08-27  8:06 ` Baolin Wang
2026-08-27 11:02   ` David Hildenbrand (Arm)
2026-08-27 12:11     ` Lance Yang
2026-08-27 14:07       ` Kiryl Shutsemau
2026-08-31 18:53         ` Pedro Demarchi Gomes [this message]
2026-09-02 10:08           ` Kiryl Shutsemau
2026-08-28  3:24       ` Pedro Demarchi Gomes

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