From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from frasgout.his.huawei.com (frasgout.his.huawei.com [185.176.79.56]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D373E35B134; Fri, 9 Jan 2026 12:30:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=185.176.79.56 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767961838; cv=none; b=q1H4tjWALW4ILAvbvJ4z0845fp8FZKc5ZMx6ONmMwpzM/3yd6GX5hiZCdWWyW9pv9BxtDaR46oXRLkS0TO0colhD4o+l273YnkrovSXc80AB6v7CiDfvjYVC4mFABIlVVI6cR/fxBEsNUYArAHFyQsbBu/7GbTxcgYP5ONEHQaQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767961838; c=relaxed/simple; bh=in5JvqRmDAdB6dX8FGI0EEgnQhCtsywKD5TDJBxjJjU=; h=Date:From:To:CC:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=UWnRPWl/bxzc3etC+D/hDMXVL629tsfTQoVOMiMHr4DXgk7pPNAhdQZEUneOc/w+kape6VZVYxiHCW05KMIS/DXjn5TcPcQvRZnq3uYsadgoSz0KFqyDJd3ziYR/+Q/KsO8k3hcZNfEBbcMg9f9FA6lIFqBpWd7JloZTbe8Sngo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com; spf=pass smtp.mailfrom=huawei.com; arc=none smtp.client-ip=185.176.79.56 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huawei.com Received: from mail.maildlp.com (unknown [172.18.224.83]) by frasgout.his.huawei.com (SkyGuard) with ESMTPS id 4dnh1h1cXTzHnH7w; Fri, 9 Jan 2026 20:30:16 +0800 (CST) Received: from dubpeml100005.china.huawei.com (unknown [7.214.146.113]) by mail.maildlp.com (Postfix) with ESMTPS id 48D4440572; Fri, 9 Jan 2026 20:30:26 +0800 (CST) Received: from localhost (10.203.177.15) by dubpeml100005.china.huawei.com (7.214.146.113) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.1544.36; Fri, 9 Jan 2026 12:30:24 +0000 Date: Thu, 8 Jan 2026 16:10:13 +0000 From: Jonathan Cameron To: John Groves CC: Miklos Szeredi , Dan Williams , Bernd Schubert , "Alison Schofield" , John Groves , Jonathan Corbet , Vishal Verma , Dave Jiang , Matthew Wilcox , Jan Kara , Alexander Viro , "David Hildenbrand" , Christian Brauner , "Darrick J . Wong" , Randy Dunlap , Jeff Layton , Amir Goldstein , Stefan Hajnoczi , Joanne Koong , Josef Bacik , Bagas Sanjaya , Chen Linxuan , "James Morse" , Fuad Tabba , "Sean Christopherson" , Shivank Garg , Ackerley Tng , Gregory Price , Aravind Ramesh , Ajay Joshi , , , , , , Subject: Re: [PATCH V3 04/21] dax: Add dax_operations for use by fs-dax on fsdev dax Message-ID: <20260108161013.00001916@huawei.com> In-Reply-To: References: <20260107153244.64703-1-john@groves.net> <20260107153332.64727-1-john@groves.net> <20260107153332.64727-5-john@groves.net> <20260108115037.00003295@huawei.com> X-Mailer: Claws Mail 4.3.0 (GTK 3.24.42; x86_64-w64-mingw32) Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit X-ClientProxiedBy: lhrpeml100010.china.huawei.com (7.191.174.197) To dubpeml100005.china.huawei.com (7.214.146.113) On Thu, 8 Jan 2026 09:59:08 -0600 John Groves wrote: > On 26/01/08 11:50AM, Jonathan Cameron wrote: > > On Wed, 7 Jan 2026 09:33:13 -0600 > > John Groves wrote: > > > > > From: John Groves > > > > > Hi John > > > > The description should generally make sense without the title. > > Sometimes that means more or less repeating the title. > > > > A few other things inline. > > Will do > > > > > > * These methods are based on pmem_dax_ops from drivers/nvdimm/pmem.c > > > * fsdev_dax_direct_access() returns the hpa, pfn and kva. The kva was > > > newly stored as dev_dax->virt_addr by dev_dax_probe(). > > > * The hpa/pfn are used for mmap (dax_iomap_fault()), and the kva is used > > > for read/write (dax_iomap_rw()) > > > * fsdev_dax_recovery_write() and dev_dax_zero_page_range() have not been > > > tested yet. I'm looking for suggestions as to how to test those. > > > * dax-private.h: add dev_dax->cached_size, which fsdev needs to > > > remember. The dev_dax size cannot change while a driver is bound > > > (dev_dax_resize returns -EBUSY if dev->driver is set). Caching the size > > > at probe time allows fsdev's direct_access path can use it without > > > acquiring dax_dev_rwsem (which isn't exported anyway). > > > > > > Signed-off-by: John Groves > > > > > diff --git a/drivers/dax/fsdev.c b/drivers/dax/fsdev.c > > > index c5c660b193e5..9e2f83aa2584 100644 > > > --- a/drivers/dax/fsdev.c > > > +++ b/drivers/dax/fsdev.c > > > @@ -27,6 +27,81 @@ > > > * - No mmap support - all access is through fs-dax/iomap > > > */ > > > > > > +static void fsdev_write_dax(void *pmem_addr, struct page *page, > > > + unsigned int off, unsigned int len) > > > +{ > > > + while (len) { > > > + void *mem = kmap_local_page(page); > > > > I guess it's pretty simple, but do we care about HIGHMEM for this > > new feature? Maybe it's just easier to support it than argue about it however ;) > > I think this compiles to zero overhead, and is an established pattern - > but I'm ok following a consensus elsewhere... That's fair, probably just keep it. > > > +static long __fsdev_dax_direct_access(struct dax_device *dax_dev, pgoff_t pgoff, > > > + long nr_pages, enum dax_access_mode mode, void **kaddr, > > > + unsigned long *pfn) > > > +{ > > > + struct dev_dax *dev_dax = dax_get_private(dax_dev); > > > + size_t size = nr_pages << PAGE_SHIFT; > > > + size_t offset = pgoff << PAGE_SHIFT; > > > + void *virt_addr = dev_dax->virt_addr + offset; > > > + phys_addr_t phys; > > > + unsigned long local_pfn; > > > + > > > + WARN_ON(!dev_dax->virt_addr); > > > + > > > + phys = dax_pgoff_to_phys(dev_dax, pgoff, nr_pages << PAGE_SHIFT); > > > > Use size given you already computed it. > > Not sure I follow. nr_pages is the size of the access or fault, not the size > of the device. Just above: size_t size = nr_pages << PAGE_SHIFT; Jonathan