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Tue, 1 Apr 2025 14:59:47 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id xZcjL2P/62ejcAAAD6G6ig (envelope-from ); Tue, 01 Apr 2025 14:59:47 +0000 Date: Tue, 1 Apr 2025 16:59:46 +0200 From: Oscar Salvador To: "Vishal Moola (Oracle)" Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, muchun.song@linux.dev, Miaohe Lin Subject: Re: [PATCH] mm/compaction: Fix bug in hugetlb handling pathway Message-ID: References: <20250401021025.637333-1-vishal.moola@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250401021025.637333-1-vishal.moola@gmail.com> X-Rspamd-Action: no action X-Rspamd-Queue-Id: BDE9A1C0006 X-Stat-Signature: agokgjd94ya9zuzx5u5h1azytm7axo8u X-Rspam-User: X-Rspamd-Server: rspam12 X-HE-Tag: 1743519589-568570 X-HE-Meta: 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 ALoyfUPm okfBBsUFuxr+7up4ttSnZfUJ5PTN74OIXweVpFkVB3EOr+cQtkwQcYK9/oVW+AmmRKmQ3fatZuOEUhdyMyos5vJ+7LTMW0XOj7VxOIopvIY/Ebhvtr0BI71tmfzfQ/HWzV2Ol8UBh9w4fLtPnDOQwSIeaD107lqXwEMPL/oWrLz22S5RXsnVboIufjG3uE2phCwpNR5HvTrhvM/L/qN8sqn7kU2ZLgAr+6bSR+IysNzLW0H+FOXc1Kdmudgl3rfBuk4JvpP+HmAwAoy5iLNEd8QWtYNcw7oPebxlJpWzmyn9DRPUSY1zR49h+skwtQORs6A8CVeqqvQ1wBToQNtWa4YSJlIyoLxrBYtAztyjg18+Y18tq59lvN37d01xZyZPnHJk4 X-Bogosity: Ham, tests=bogofilter, spamicity=0.001244, 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, Mar 31, 2025 at 07:10:24PM -0700, Vishal Moola (Oracle) wrote: > The compaction code doesn't take references on pages until we're certain > we should attempt to handle it. > > In the hugetlb case, isolate_or_dissolve_huge_page() may return -EBUSY > without taking a reference to the folio associated with our pfn. If our > folio's refcount drops to 0, compound_nr() becomes unpredictable, making > low_pfn and nr_scanned unreliable. > The user-visible effect is minimal - this should rarely happen (if ever). So, with compound_order() we either return the real order of the compound page or '0', right? > Fix this by storing the folio statistics earlier on the stack (just like > the THP and Buddy cases). > > Also revert commit 66fe1cf7f581 ("mm: compaction: use helper compound_nr > in isolate_migratepages_block") > to make backporting easier. > > Fixes: 369fa227c219 ("mm: make alloc_contig_range handle free hugetlb pages") > Cc: Miaohe Lin > Cc: Oscar Salvador > Signed-off-by: Vishal Moola (Oracle) Acked-by: Oscar Salvador -- Oscar Salvador SUSE Labs