From: Kiryl Shutsemau <kirill@shutemov.name>
To: Lance Yang <lance.yang@linux.dev>
Cc: david@kernel.org, baolin.wang@linux.alibaba.com,
pedrodemargomes@gmail.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: Thu, 27 Aug 2026 15:07:10 +0100 [thread overview]
Message-ID: <apBB01VBbmV28gWP@thinkstation> (raw)
In-Reply-To: <20260827121151.7837-1-lance.yang@linux.dev>
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
--
Kiryl Shutsemau / Kirill A. Shutemov
next prev parent reply other threads:[~2026-08-27 14:07 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-08-25 19:24 [PATCH mm-stable] mm/khugepaged: avoid unnecessary checking for swap entries when collapsing a mTHP 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 [this message]
2026-08-28 3:24 ` Pedro Demarchi Gomes
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