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Thu, 4 Apr 2024 11:11:40 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap2.dmz-prg2.suse.org with ESMTPSA id 9dHQGuyKDmYMRwAAn2gu4w (envelope-from ); Thu, 04 Apr 2024 11:11:40 +0000 Date: Thu, 4 Apr 2024 13:13:08 +0200 From: Oscar Salvador To: Matthew Wilcox Cc: Muchun Song , Andrew Morton , linux-mm@kvack.org Subject: Re: [PATCH] hugetlb: Convert alloc_buddy_hugetlb_folio to use a folio Message-ID: References: <20240402200656.913841-1-willy@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Action: no action X-Rspam-User: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 69D1E180019 X-Stat-Signature: o8pzwfbda4y4m5u89bfj19gmfaki1qpk X-HE-Tag: 1712229102-875295 X-HE-Meta: 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 OUsPlImw gC4tiUdB/SdF/geJUbSzHXFRiGuxTYLSjYtRaYAal73kWeBC2OxUip1TKtPxt93zD1nStQdQ/IPE8SA5OuICpChJAz9A+FrWovKdqdirp+BdOOSRbkZ1beKcCcD+2dfuYKy/SV+IAHObmxzbPLN0SpJHRSv3hQCnK/qRSxKn+q5eztxea6DZtIxe58z4R0ANr24X6WIwQhEAifEO3RDBcjPuTJeXFcaUqprSl6L9rxa6JuTAgl8NTBOHojheQGMu3BFOsDdgt9SB0MLRlMP2xxE+Ek3XCWZXZnHkpZQ5eBXLeOvTRK8mat9WnMg== 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 Wed, Apr 03, 2024 at 10:17:45PM +0100, Matthew Wilcox wrote: > I think hugetlb is being unnecessarily paranoid here, tbh. Or maybe > this part is just badly structured; if we're allocating a hugetlb folio, > it should be fine for its refcount to be temporarily elevated by someone > else. Not sure I can figure out what's going on in > alloc_and_dissolve_hugetlb_folio() though. AFAICR, the problem comes when we need to remap the pages for vmemmap optimization [1]. So, IIUC: 1) if someone comes around and grabs a refcount (say something doing speculative stuff) 2) we do the remapping 3) that someone who took the refcount, now does a put_page() 4) vmemmap no longer points to the old page but the new one, meaning that that 'put_page()' is done on the wrong page. @Munchun: Did I get this right? [1] https://lore.kernel.org/linux-mm/YupRjWRiz4lPo+y7@FVFYT0MHHV2J/ -- Oscar Salvador SUSE Labs