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From: Lance Yang In-Reply-To: <8cd717a3-b149-4eb9-88d2-ea4b9b1112f5@lucifer.local> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 525ED18001A X-Stat-Signature: 8qtdpnhmw4zqnzeiwtk9n8oby3eg15jt X-HE-Tag: 1758016860-640201 X-HE-Meta: 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 kjR0lKm0 +OZJFX8dsLlal3Jy4P0DeyhYLS8tiPXur9OLp/gOEOUcFCzH6iLcrD8upJxS9ERV/AwO6v3nzQEwuouYbJDaOifNVj7vWYKOU1SgtsjAPXKoBR0jI5h/6elIa1JWi9c+JQU4hJsdKfO7LMyYYNDHtOthLbim8bE91JcNf+Ew4mH4MVEHj/WEHxR3W5vyC3hPDowy0CR13eR57i06Y5FRaiBXa6/ivSAVd0AWDEBZPeUkJpMBmacnaNeJZwk6cVIdmAALf X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2025/9/16 17:58, Lorenzo Stoakes wrote: > On Tue, Sep 16, 2025 at 10:48:22AM +0100, Kiryl Shutsemau wrote: >> On Tue, Sep 16, 2025 at 10:39:53AM +0100, Lorenzo Stoakes wrote: >>> On Tue, Sep 16, 2025 at 10:29:11AM +0100, Kiryl Shutsemau wrote: >>>> On Tue, Sep 16, 2025 at 02:21:26PM +0800, Lance Yang wrote: >>>>> Users of mlock() expect low and predictable latency. THP collapse is a >>>>> heavy operation that introduces exactly the kind of unpredictable delays >>>>> they want to avoid. It has to unmap PTEs, copy data from the small folios >>>>> to a new THP, and then remap the THP back to the PMD ;) >>>> >>>> Generally, we allow minor page faults into mlocked VMAs and avoid major. >>>> This is minor page fault territory in my view. >>> >>> Hm, but we won't be causing minor faults via reclaim right, since they're >>> not on any LRU? >> >> PTEs are still present when we do THP allocation. No reclaim while the >> access is blocked. We only block the access on copy and PTEs->PMD >> collapse. > > Right indeed, esp. with compaction being allowed for mlock, I agree with you > that this patch should be dropped :) Got it. Will do ;) Thanks, Lance