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X-CSE-ConnectionGUID: tC8lp0yzS/mEYVbE19V6Wg== X-CSE-MsgGUID: SlkHRbaVQTGfP8Um4n48Gw== X-IronPort-AV: E=McAfee;i="6800,10657,11841"; a="71854366" X-IronPort-AV: E=Sophos;i="6.25,154,1779174000"; d="scan'208";a="71854366" Received: from fmviesa003.fm.intel.com ([10.60.135.143]) by fmvoesa110.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 09 Jul 2026 14:07:22 -0700 X-CSE-ConnectionGUID: HCOrVRvIQYiPh/zZ0nyc9g== X-CSE-MsgGUID: ZJq6SJJxQbec8bcZ2BSGCQ== X-ExtLoop1: 1 Received: from bradocaj-mobl.ger.corp.intel.com (HELO [10.125.111.142]) ([10.125.111.142]) by fmviesa003-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 09 Jul 2026 14:07:20 -0700 Message-ID: <8ad8e025-ffea-4bc8-8797-6a280ecc229f@intel.com> Date: Thu, 9 Jul 2026 14:07:19 -0700 Precedence: bulk X-Mailing-List: driver-core@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 07/10] dax: plumb hotplug online_type through dax To: Gregory Price , linux-mm@kvack.org Cc: nvdimm@lists.linux.dev, linux-kernel@vger.kernel.org, linux-cxl@vger.kernel.org, driver-core@lists.linux.dev, linux-kselftest@vger.kernel.org, kernel-team@meta.com, david@kernel.org, osalvador@suse.de, gregkh@linuxfoundation.org, rafael@kernel.org, dakr@kernel.org, djbw@kernel.org, vishal.l.verma@intel.com, alison.schofield@intel.com, akpm@linux-foundation.org, ljs@kernel.org, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, shuah@kernel.org, iweiny@kernel.org, Smita.KoralahalliChannabasappa@amd.com, apopple@nvidia.com References: <20260630211842.2252800-1-gourry@gourry.net> <20260630211842.2252800-8-gourry@gourry.net> Content-Language: en-US From: Dave Jiang In-Reply-To: <20260630211842.2252800-8-gourry@gourry.net> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 6/30/26 2:18 PM, Gregory Price wrote: > There is no way for drivers leveraging dax_kmem to plumb through a > preferred auto-online policy - the system default policy is forced. > > Add 'enum mmop' field to DAX device creation path to allow drivers > to specify an auto-online policy when using the kmem driver. > > Capturing the system default would otherwise break the ABI, because > the system default can change - but we would be statically assigning > the value at device creation time. > > To resolve this we add DAX_ONLINE_DEFAULT, which defaults devices to > the current behavior, while providing a clean way to override it. > > No behavioural change for existing callers (still the system default). behavioral > > Signed-off-by: Gregory Price Reviewed-by: Dave Jiang > --- > drivers/dax/bus.c | 3 +++ > drivers/dax/bus.h | 9 +++++++++ > drivers/dax/cxl.c | 1 + > drivers/dax/dax-private.h | 4 ++++ > drivers/dax/hmem/hmem.c | 1 + > drivers/dax/kmem.c | 11 +++++++++-- > drivers/dax/pmem.c | 1 + > 7 files changed, 28 insertions(+), 2 deletions(-) > > diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c > index 492573b47f66..4a03b323b003 100644 > --- a/drivers/dax/bus.c > +++ b/drivers/dax/bus.c > @@ -1,6 +1,7 @@ > // SPDX-License-Identifier: GPL-2.0 > /* Copyright(c) 2017-2018 Intel Corporation. All rights reserved. */ > #include > +#include > #include > #include > #include > @@ -394,6 +395,7 @@ static ssize_t create_store(struct device *dev, struct device_attribute *attr, > .size = 0, > .id = -1, > .memmap_on_memory = false, > + .online_type = DAX_ONLINE_DEFAULT, > }; > struct dev_dax *dev_dax = __devm_create_dev_dax(&data); > > @@ -1527,6 +1529,7 @@ static struct dev_dax *__devm_create_dev_dax(struct dev_dax_data *data) > ida_init(&dev_dax->ida); > > dev_dax->memmap_on_memory = data->memmap_on_memory; > + dev_dax->online_type = data->online_type; > > inode = dax_inode(dax_dev); > dev->devt = inode->i_rdev; > diff --git a/drivers/dax/bus.h b/drivers/dax/bus.h > index 5909171a4428..3bc76bc0a145 100644 > --- a/drivers/dax/bus.h > +++ b/drivers/dax/bus.h > @@ -3,6 +3,7 @@ > #ifndef __DAX_BUS_H__ > #define __DAX_BUS_H__ > #include > +#include > #include > #include > #include > @@ -16,6 +17,13 @@ struct dax_region; > #define IORESOURCE_DAX_STATIC BIT(0) > #define IORESOURCE_DAX_KMEM BIT(1) > > +/* > + * online_type sentinel: the device was created without an explicit online > + * policy, so the system default is resolved when the kmem driver binds, > + * (not at device-creation time, which would freeze a stale policy). > + */ > +#define DAX_ONLINE_DEFAULT (-1) > + > struct dax_region *alloc_dax_region(struct device *parent, int region_id, > struct range *range, int target_node, unsigned int align, > unsigned long flags); > @@ -26,6 +34,7 @@ struct dev_dax_data { > resource_size_t size; > int id; > bool memmap_on_memory; > + int online_type; /* enum mmop, or DAX_ONLINE_DEFAULT sentinel */ > }; > > struct dev_dax *devm_create_dev_dax(struct dev_dax_data *data); > diff --git a/drivers/dax/cxl.c b/drivers/dax/cxl.c > index 3ab39b77843d..1a7ec6212213 100644 > --- a/drivers/dax/cxl.c > +++ b/drivers/dax/cxl.c > @@ -27,6 +27,7 @@ static int cxl_dax_region_probe(struct device *dev) > .id = -1, > .size = range_len(&cxlr_dax->hpa_range), > .memmap_on_memory = true, > + .online_type = DAX_ONLINE_DEFAULT, > }; > > return PTR_ERR_OR_ZERO(devm_create_dev_dax(&data)); > diff --git a/drivers/dax/dax-private.h b/drivers/dax/dax-private.h > index 81e4af49e39c..902e922dc4e4 100644 > --- a/drivers/dax/dax-private.h > +++ b/drivers/dax/dax-private.h > @@ -8,6 +8,7 @@ > #include > #include > #include > +#include > > /* private routines between core files */ > struct dax_device; > @@ -79,6 +80,8 @@ struct dev_dax_range { > * @dev: device core > * @pgmap: pgmap for memmap setup / lifetime (driver owned) > * @memmap_on_memory: allow kmem to put the memmap in the memory > + * @online_type: MMOP_* online type for memory hotplug, or DAX_ONLINE_DEFAULT > + * to resolve the system default policy when kmem binds > * @nr_range: size of @ranges > * @ranges: range tuples of memory used > */ > @@ -95,6 +98,7 @@ struct dev_dax { > struct device dev; > struct dev_pagemap *pgmap; > bool memmap_on_memory; > + int online_type; /* enum mmop, or DAX_ONLINE_DEFAULT sentinel */ > int nr_range; > struct dev_dax_range *ranges; > }; > diff --git a/drivers/dax/hmem/hmem.c b/drivers/dax/hmem/hmem.c > index af21f66bf872..2de3bc925172 100644 > --- a/drivers/dax/hmem/hmem.c > +++ b/drivers/dax/hmem/hmem.c > @@ -37,6 +37,7 @@ static int dax_hmem_probe(struct platform_device *pdev) > .id = -1, > .size = region_idle ? 0 : range_len(&mri->range), > .memmap_on_memory = false, > + .online_type = DAX_ONLINE_DEFAULT, > }; > > return PTR_ERR_OR_ZERO(devm_create_dev_dax(&data)); > diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c > index 592171ec10f4..0a184c0878dd 100644 > --- a/drivers/dax/kmem.c > +++ b/drivers/dax/kmem.c > @@ -72,6 +72,7 @@ static int dev_dax_kmem_probe(struct dev_dax *dev_dax) > int i, rc, mapped = 0; > mhp_t mhp_flags; > int numa_node; > + int online_type; > int adist = MEMTIER_DEFAULT_DAX_ADISTANCE; > > /* > @@ -132,6 +133,11 @@ static int dev_dax_kmem_probe(struct dev_dax *dev_dax) > goto err_reg_mgid; > data->mgid = rc; > > + /* Resolve system default at bind time in case it changed */ > + online_type = dev_dax->online_type; > + if (online_type == DAX_ONLINE_DEFAULT) > + online_type = mhp_get_default_online_type(); > + > for (i = 0; i < dev_dax->nr_range; i++) { > struct resource *res; > struct range range; > @@ -172,8 +178,9 @@ static int dev_dax_kmem_probe(struct dev_dax *dev_dax) > * Ensure that future kexec'd kernels will not treat > * this as RAM automatically. > */ > - rc = add_memory_driver_managed(data->mgid, range.start, > - range_len(&range), kmem_name, mhp_flags); > + rc = __add_memory_driver_managed(data->mgid, range.start, > + range_len(&range), kmem_name, mhp_flags, > + online_type); > > if (rc) { > dev_warn(dev, "mapping%d: %#llx-%#llx memory add failed\n", > diff --git a/drivers/dax/pmem.c b/drivers/dax/pmem.c > index bee93066a849..e7adace69195 100644 > --- a/drivers/dax/pmem.c > +++ b/drivers/dax/pmem.c > @@ -63,6 +63,7 @@ static struct dev_dax *__dax_pmem_probe(struct device *dev) > .pgmap = &pgmap, > .size = range_len(&range), > .memmap_on_memory = false, > + .online_type = DAX_ONLINE_DEFAULT, > }; > > return devm_create_dev_dax(&data);