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Date:   Mon, 30 Oct 2023 10:57:42 +0800
From:   "Huang, Ying" <ying.huang@...el.com>
To:     Vishal Verma <vishal.l.verma@...el.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...hat.com>,
        Oscar Salvador <osalvador@...e.de>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
        <nvdimm@...ts.linux.dev>, <linux-cxl@...r.kernel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>,
        Michal Hocko <mhocko@...e.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Jeff Moyer <jmoyer@...hat.com>
Subject: Re: [PATCH v7 3/3] dax/kmem: allow kmem to add memory with
 memmap_on_memory

Vishal Verma <vishal.l.verma@...el.com> writes:

> Large amounts of memory managed by the kmem driver may come in via CXL,
> and it is often desirable to have the memmap for this memory on the new
> memory itself.
>
> Enroll kmem-managed memory for memmap_on_memory semantics if the dax
> region originates via CXL. For non-CXL dax regions, retain the existing
> default behavior of hot adding without memmap_on_memory semantics.
>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: David Hildenbrand <david@...hat.com>
> Cc: Michal Hocko <mhocko@...e.com>
> Cc: Oscar Salvador <osalvador@...e.de>
> Cc: Dan Williams <dan.j.williams@...el.com>
> Cc: Dave Jiang <dave.jiang@...el.com>
> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> Cc: Huang Ying <ying.huang@...el.com>
> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
> Reviewed-by: David Hildenbrand <david@...hat.com>
> Signed-off-by: Vishal Verma <vishal.l.verma@...el.com>

LGTM, Thanks!

Reviewed-by: "Huang, Ying" <ying.huang@...el.com>

> ---
>  drivers/dax/bus.h         | 1 +
>  drivers/dax/dax-private.h | 1 +
>  drivers/dax/bus.c         | 3 +++
>  drivers/dax/cxl.c         | 1 +
>  drivers/dax/hmem/hmem.c   | 1 +
>  drivers/dax/kmem.c        | 8 +++++++-
>  drivers/dax/pmem.c        | 1 +
>  7 files changed, 15 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/dax/bus.h b/drivers/dax/bus.h
> index 1ccd23360124..cbbf64443098 100644
> --- a/drivers/dax/bus.h
> +++ b/drivers/dax/bus.h
> @@ -23,6 +23,7 @@ struct dev_dax_data {
>  	struct dev_pagemap *pgmap;
>  	resource_size_t size;
>  	int id;
> +	bool memmap_on_memory;
>  };
>  
>  struct dev_dax *devm_create_dev_dax(struct dev_dax_data *data);
> diff --git a/drivers/dax/dax-private.h b/drivers/dax/dax-private.h
> index 27cf2daaaa79..446617b73aea 100644
> --- a/drivers/dax/dax-private.h
> +++ b/drivers/dax/dax-private.h
> @@ -70,6 +70,7 @@ struct dev_dax {
>  	struct ida ida;
>  	struct device dev;
>  	struct dev_pagemap *pgmap;
> +	bool memmap_on_memory;
>  	int nr_range;
>  	struct dev_dax_range {
>  		unsigned long pgoff;
> diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c
> index 0ee96e6fc426..ad9f821b8c78 100644
> --- a/drivers/dax/bus.c
> +++ b/drivers/dax/bus.c
> @@ -367,6 +367,7 @@ static ssize_t create_store(struct device *dev, struct device_attribute *attr,
>  			.dax_region = dax_region,
>  			.size = 0,
>  			.id = -1,
> +			.memmap_on_memory = false,
>  		};
>  		struct dev_dax *dev_dax = devm_create_dev_dax(&data);
>  
> @@ -1400,6 +1401,8 @@ struct dev_dax *devm_create_dev_dax(struct dev_dax_data *data)
>  	dev_dax->align = dax_region->align;
>  	ida_init(&dev_dax->ida);
>  
> +	dev_dax->memmap_on_memory = data->memmap_on_memory;
> +
>  	inode = dax_inode(dax_dev);
>  	dev->devt = inode->i_rdev;
>  	dev->bus = &dax_bus_type;
> diff --git a/drivers/dax/cxl.c b/drivers/dax/cxl.c
> index 8bc9d04034d6..c696837ab23c 100644
> --- a/drivers/dax/cxl.c
> +++ b/drivers/dax/cxl.c
> @@ -26,6 +26,7 @@ static int cxl_dax_region_probe(struct device *dev)
>  		.dax_region = dax_region,
>  		.id = -1,
>  		.size = range_len(&cxlr_dax->hpa_range),
> +		.memmap_on_memory = true,
>  	};
>  
>  	return PTR_ERR_OR_ZERO(devm_create_dev_dax(&data));
> diff --git a/drivers/dax/hmem/hmem.c b/drivers/dax/hmem/hmem.c
> index 5d2ddef0f8f5..b9da69f92697 100644
> --- a/drivers/dax/hmem/hmem.c
> +++ b/drivers/dax/hmem/hmem.c
> @@ -36,6 +36,7 @@ static int dax_hmem_probe(struct platform_device *pdev)
>  		.dax_region = dax_region,
>  		.id = -1,
>  		.size = region_idle ? 0 : range_len(&mri->range),
> +		.memmap_on_memory = false,
>  	};
>  
>  	return PTR_ERR_OR_ZERO(devm_create_dev_dax(&data));
> diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c
> index c57acb73e3db..0aa6c45a4e5a 100644
> --- a/drivers/dax/kmem.c
> +++ b/drivers/dax/kmem.c
> @@ -12,6 +12,7 @@
>  #include <linux/mm.h>
>  #include <linux/mman.h>
>  #include <linux/memory-tiers.h>
> +#include <linux/memory_hotplug.h>
>  #include "dax-private.h"
>  #include "bus.h"
>  
> @@ -56,6 +57,7 @@ static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
>  	unsigned long total_len = 0;
>  	struct dax_kmem_data *data;
>  	int i, rc, mapped = 0;
> +	mhp_t mhp_flags;
>  	int numa_node;
>  
>  	/*
> @@ -136,12 +138,16 @@ static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
>  		 */
>  		res->flags = IORESOURCE_SYSTEM_RAM;
>  
> +		mhp_flags = MHP_NID_IS_MGID;
> +		if (dev_dax->memmap_on_memory)
> +			mhp_flags |= MHP_MEMMAP_ON_MEMORY;
> +
>  		/*
>  		 * 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_NID_IS_MGID);
> +				range_len(&range), kmem_name, mhp_flags);
>  
>  		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 ae0cb113a5d3..f3c6c67b8412 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)
>  		.id = id,
>  		.pgmap = &pgmap,
>  		.size = range_len(&range),
> +		.memmap_on_memory = false,
>  	};
>  
>  	return devm_create_dev_dax(&data);

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