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Received: from willy by casper.infradead.org with local (Exim 4.97.1 #2 (Red Hat Linux)) id 1s7IyG-0000000AkmV-1EXu; Wed, 15 May 2024 18:03:20 +0000 Date: Wed, 15 May 2024 19:03:20 +0100 From: Matthew Wilcox To: "Pankaj Raghav (Samsung)" Cc: david@fromorbit.com, djwong@kernel.org, hch@lst.de, Keith Busch , mcgrof@kernel.org, akpm@linux-foundation.org, brauner@kernel.org, chandan.babu@oracle.com, gost.dev@samsung.com, hare@suse.de, john.g.garry@oracle.com, linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-xfs@vger.kernel.org, p.raghav@samsung.com, ritesh.list@gmail.com, ziy@nvidia.com Subject: Re: [RFC] iomap: use huge zero folio in iomap_dio_zero Message-ID: References: <20240503095353.3798063-8-mcgrof@kernel.org> <20240507145811.52987-1-kernel@pankajraghav.com> <20240515155943.2uaa23nvddmgtkul@quentin> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240515155943.2uaa23nvddmgtkul@quentin> X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: B598140025 X-Rspam-User: X-Stat-Signature: i1o5sbedr5d4fhghrqcfrszko54txhtx X-HE-Tag: 1715796213-803837 X-HE-Meta: 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 KkfhIaGN 5tRt6Sraihd3H1RYcBl+oZa1swhT3QSSHJGH7tR4x9CzrZSd56nA6liVC5rdwpAxHi8oq45nVl3HHG0RpnuIO5kfxmNdGlMngvXzt0B4NEk4lQPM6MguEH659naBsIzdz+1npi3mI0t3WDzg+xsAljA4WDe61XqTdzEnsNQcWFAImDQWss7oyAsLCUtj3H9E1w226kVqfILCUFZ5vrsTeaurbPI8QnuYdc7S5ql9vurntAwDy2ndPG8R9nwu5I3qWmml4 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, May 15, 2024 at 03:59:43PM +0000, Pankaj Raghav (Samsung) wrote: > static int __init iomap_init(void) > { > + void *addr = kzalloc(16 * PAGE_SIZE, GFP_KERNEL); Don't use XFS coding style outside XFS. kzalloc() does not guarantee page alignment much less alignment to a folio. It happens to work today, but that is an implementation artefact. > + > + if (!addr) > + return -ENOMEM; > + > + zero_fsb_folio = virt_to_folio(addr); We also don't guarantee that calling kzalloc() gives you a virtual address that can be converted to a folio. You need to allocate a folio to be sure that you get a folio. Of course, you don't actually need a folio. You don't need any of the folio metadata and can just use raw pages. > + /* > + * The zero folio used is 64k. > + */ > + WARN_ON_ONCE(len > (16 * PAGE_SIZE)); PAGE_SIZE is not necessarily 4KiB. > + bio = iomap_dio_alloc_bio(iter, dio, BIO_MAX_VECS, > + REQ_OP_WRITE | REQ_SYNC | REQ_IDLE); The point was that we now only need one biovec, not MAX.