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Mon, 8 Sep 2025 07:44:31 -0400 (EDT) Date: Mon, 8 Sep 2025 12:44:29 +0100 From: Kiryl Shutsemau To: David Hildenbrand Cc: Lance Yang , akpm@linux-foundation.org, Liam.Howlett@oracle.com, baohua@kernel.org, baolin.wang@linux.alibaba.com, dev.jain@arm.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, lorenzo.stoakes@oracle.com, npache@redhat.com, ryan.roberts@arm.com, usamaarif642@gmail.com, ziy@nvidia.com Subject: Re: [PATCH v2 1/1] mm: skip mlocked THPs that are underused early in deferred_split_scan() Message-ID: <5j6i2o6umqwxabdfncbrdytmvdma4yrraxe6hu4csckcniduya@sm3mlablwbad> References: <20250908090741.61519-1-lance.yang@linux.dev> <9a0c07b9-5bf0-4251-8609-fbaf0ca75bf9@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <9a0c07b9-5bf0-4251-8609-fbaf0ca75bf9@redhat.com> X-Rspamd-Queue-Id: 2F09B20009 X-Stat-Signature: p8dqio6niu5jpotsjd4d4e4gwpdrmumt X-Rspam-User: X-Rspamd-Server: rspam06 X-HE-Tag: 1757331875-613838 X-HE-Meta: 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 uRuFR465 u3aUToiCRYC7UmfdqaqiLoLNocfivLaU3lPIKzA3jfDOHLmHT5/xyUQNff2+MORTLTTCyoTxy3pYnkt7zMBV2jkLBwIdhsHJw541IgYnc9D5zjTeYp0AnyoTb4eqnfAUVVVWA2tLDts8DnL3cNz07NPrHecedvo7h7VtltKau4wxddL39xe8xnZ9X/UNEaUe2+EnKUQk+MxR6h7WeTw2zoEB3VvS/0dVNXzzuU6xdhTpDo8LM7EzO4eIKwT9qq9LduTvGhoDFB8Mzjuyn4n0AQtsEpHZ4yyqS0ytLRx7FOu2gv4wR5EBCrPGnhvwyuL9UUI+mXc6kRRMywfVsYoyIWj58PYo8nvbtDj+a3e9EWFRzR8DJnTYFRy7Nd7TTZG2kFXdoMx1jdoAJp0hBrqaBi33P/1PeayFMPsA3UdfNQTICA3aMJT8+odVpo1xxJa7QZsAmJ7phviMCUys= 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 Mon, Sep 08, 2025 at 01:32:05PM +0200, David Hildenbrand wrote: > On 08.09.25 12:38, Kiryl Shutsemau wrote: > > On Mon, Sep 08, 2025 at 05:07:41PM +0800, Lance Yang wrote: > > > From: Lance Yang > > > > > > When we stumble over a fully-mapped mlocked THP in the deferred shrinker, > > > it does not make sense to try to detect whether it is underused, because > > > try_to_map_unused_to_zeropage(), called while splitting the folio, will not > > > actually replace any zeroed pages by the shared zeropage. > > > > It makes me think, does KSM follows the same logic as > > try_to_map_unused_to_zeropage()? > > > > I cannot immediately find what prevents KSM from replacing zeroed mlocked > > folio with ZERO_PAGE(). > > > > Hm? > > I assume if you're using mlock and at the same time enable KSM for a > process/VMA, you're doing something wrong. > > In contrast, THP is supposed to be transparent (yeah, I know ...). Yeah, I guess it is user error. Maybe we should make ksm_compatible() return false for VM_LOCKED? KSM breaks mlock() contract. But it can be risky if someone already relies on this broken behaviour. -- Kiryl Shutsemau / Kirill A. Shutemov