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d=hostedemail.com; t=1719466249; a=rsa-sha256; cv=none; b=Hmnasuy939bewWQL2Hjm/Jw60wnyLUAWE5TxEcr4CY1zAN+JJeLTP2cA9praSOdFriaakW o6tUncXxNLz3/abCHoCVdhw4E1SSLE5Fz/L2cglfrbXgR+ExKL1wpKeUdKO4wD5k2LdUp9 xhScCs+7z2yMR4tZfaXw1FdSK9+liYA= ARC-Authentication-Results: i=1; imf10.hostedemail.com; dkim=none; spf=pass (imf10.hostedemail.com: domain of hch@lst.de designates 213.95.11.211 as permitted sender) smtp.mailfrom=hch@lst.de; dmarc=none Received: by verein.lst.de (Postfix, from userid 2407) id 9748A68AFE; Thu, 27 Jun 2024 07:30:59 +0200 (CEST) Date: Thu, 27 Jun 2024 07:30:59 +0200 From: Christoph Hellwig To: Alistair Popple Cc: dan.j.williams@intel.com, vishal.l.verma@intel.com, dave.jiang@intel.com, logang@deltatee.com, bhelgaas@google.com, jack@suse.cz, jgg@ziepe.ca, catalin.marinas@arm.com, will@kernel.org, mpe@ellerman.id.au, npiggin@gmail.com, dave.hansen@linux.intel.com, ira.weiny@intel.com, willy@infradead.org, djwong@kernel.org, tytso@mit.edu, linmiaohe@huawei.com, david@redhat.com, peterx@redhat.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, nvdimm@lists.linux.dev, linux-cxl@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-ext4@vger.kernel.org, linux-xfs@vger.kernel.org, jhubbard@nvidia.com, hch@lst.de, david@fromorbit.com Subject: Re: [PATCH 02/13] pci/p2pdma: Don't initialise page refcount to one Message-ID: <20240627053059.GB14837@lst.de> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 39553C000F X-Stat-Signature: 4hgtzz1egajufi1gnbtoixpqoqw9tdhu X-HE-Tag: 1719466265-949181 X-HE-Meta: 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 DZUZULLY RJ7yPP+fvhfYFRrkdj0xeGA0ZE3Tvn97ezmTcP6VqcdPCuk2k47i6JlW6Rzk+HEnzX0nxgpVKHH0Bh/CrAtddkI6M3dghBw/l3Lfs 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 Thu, Jun 27, 2024 at 10:54:17AM +1000, Alistair Popple wrote: > The reference counts for ZONE_DEVICE private pages should be > initialised by the driver when the page is actually allocated by the > driver allocator, not when they are first created. This is currently > the case for MEMORY_DEVICE_PRIVATE and MEMORY_DEVICE_COHERENT pages > but not MEMORY_DEVICE_PCI_P2PDMA pages so fix that up. > > Signed-off-by: Alistair Popple > --- > drivers/pci/p2pdma.c | 2 ++ > mm/memremap.c | 8 ++++---- > mm/mm_init.c | 4 +++- > 3 files changed, 9 insertions(+), 5 deletions(-) > > diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c > index 4f47a13..1e9ea32 100644 > --- a/drivers/pci/p2pdma.c > +++ b/drivers/pci/p2pdma.c > @@ -128,6 +128,8 @@ static int p2pmem_alloc_mmap(struct file *filp, struct kobject *kobj, > goto out; > } > > + set_page_count(virt_to_page(kaddr), 1); Can we have a comment here? Without that it feels a bit too much like black magic when reading the code. > + if (folio->page.pgmap->type == MEMORY_DEVICE_PRIVATE || > + folio->page.pgmap->type == MEMORY_DEVICE_COHERENT) > + put_dev_pagemap(folio->page.pgmap); > + else if (folio->page.pgmap->type != MEMORY_DEVICE_PCI_P2PDMA) > /* > * Reset the refcount to 1 to prepare for handing out the page > * again. > */ > folio_set_count(folio, 1); Where the else if evaluates to MEMORY_DEVICE_FS_DAX || MEMORY_DEVICE_GENERIC. Maybe make this a switch statement handling all cases of the enum to make it clear and have the compiler generate a warning when a new type is added without being handled here? > @@ -1014,7 +1015,8 @@ static void __ref __init_zone_device_page(struct page *page, unsigned long pfn, > * which will set the page count to 1 when allocating the page. > */ > if (pgmap->type == MEMORY_DEVICE_PRIVATE || > + pgmap->type == MEMORY_DEVICE_COHERENT || > + pgmap->type == MEMORY_DEVICE_PCI_P2PDMA) > set_page_count(page, 0); Similarly here a switch with explanation of what will be handled and what not would be nice.