Re: [PATCH 4/4] drm/pagemap: Enable THP support for GPU memory migration

[Matthew Brost <matthew.brost@intel.com>]

On Tue, Dec 16, 2025 at 09:10:14PM +0100, Francois Dugast wrote:
> This enables support for Transparent Huge Pages (THP) for device pages by
> using MIGRATE_VMA_SELECT_COMPOUND during migration. It removes the need to
> split folios and loop multiple times over all pages to perform required
> operations at page level. Instead, we rely on newly introduced support for
> higher orders in drm_pagemap and folio-level API.
> 
> In Xe, this drastically improves performance when using SVM. The GT stats
> below collected after a 2MB page fault show overall servicing is more than
> 7 times faster, and thanks to reduced CPU overhead the time spent on the
> actual copy goes from 23% without THP to 80% with THP:
> 
> Without THP:
> 
>     svm_2M_pagefault_us: 966
>     svm_2M_migrate_us: 942
>     svm_2M_device_copy_us: 223
>     svm_2M_get_pages_us: 9
>     svm_2M_bind_us: 10
> 
> With THP:
> 
>     svm_2M_pagefault_us: 132
>     svm_2M_migrate_us: 128
>     svm_2M_device_copy_us: 106
>     svm_2M_get_pages_us: 1
>     svm_2M_bind_us: 2
> 
> Cc: Matthew Brost <matthew.brost@intel.com>
> Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> Cc: Michal Mrozek <michal.mrozek@intel.com>
> Signed-off-by: Francois Dugast <francois.dugast@intel.com>
> ---
>  drivers/gpu/drm/drm_pagemap.c | 88 +++++++++++++++++++++++++++++------
>  drivers/gpu/drm/xe/xe_svm.c   |  5 ++
>  include/drm/drm_pagemap.h     |  5 +-
>  3 files changed, 83 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_pagemap.c b/drivers/gpu/drm/drm_pagemap.c
> index b71e47136112..797ec2094fdf 100644
> --- a/drivers/gpu/drm/drm_pagemap.c
> +++ b/drivers/gpu/drm/drm_pagemap.c
> @@ -211,16 +211,20 @@ void *drm_pagemap_page_zone_device_data(struct page *page)
>  /**
>   * drm_pagemap_get_devmem_page() - Get a reference to a device memory page
>   * @page: Pointer to the page
> + * @order: Order
>   * @zdd: Pointer to the GPU SVM zone device data
>   *
>   * This function associates the given page with the specified GPU SVM zone
>   * device data and initializes it for zone device usage.
>   */
>  static void drm_pagemap_get_devmem_page(struct page *page,
> +					unsigned int order,
>  					struct drm_pagemap_zdd *zdd)
>  {
> -	page->zone_device_data = drm_pagemap_zdd_get(zdd);
> -	zone_device_page_init(page, 0);
> +	struct folio *folio = page_folio(page);
> +
> +	folio_set_zone_device_data(folio, drm_pagemap_zdd_get(zdd));
> +	zone_device_page_init(page, order);
>  }
>  
>  /**
> @@ -345,11 +349,13 @@ int drm_pagemap_migrate_to_devmem(struct drm_pagemap_devmem *devmem_allocation,
>  				  void *pgmap_owner)
>  {
>  	const struct drm_pagemap_devmem_ops *ops = devmem_allocation->ops;
> +	struct drm_pagemap *dpagemap = devmem_allocation->dpagemap;
>  	struct migrate_vma migrate = {
>  		.start		= start,
>  		.end		= end,
>  		.pgmap_owner	= pgmap_owner,
> -		.flags		= MIGRATE_VMA_SELECT_SYSTEM,
> +		.flags		= MIGRATE_VMA_SELECT_SYSTEM
> +				| MIGRATE_VMA_SELECT_COMPOUND,
>  	};
>  	unsigned long i, npages = npages_in_range(start, end);
>  	struct vm_area_struct *vas;
> @@ -409,11 +415,6 @@ int drm_pagemap_migrate_to_devmem(struct drm_pagemap_devmem *devmem_allocation,
>  		goto err_free;
>  	}
>  
> -	if (migrate.cpages != npages) {

I don't we want to blindly delete this. I believe if the original check
fails, call a subsequent function to calculate cpages based on the pages
in returned migrate.src, if that doesn't match npages bail out.

> -		err = -EBUSY;
> -		goto err_finalize;
> -	}
> -
>  	err = ops->populate_devmem_pfn(devmem_allocation, npages, migrate.dst);
>  	if (err)
>  		goto err_finalize;
> @@ -424,13 +425,38 @@ int drm_pagemap_migrate_to_devmem(struct drm_pagemap_devmem *devmem_allocation,
>  	if (err)
>  		goto err_finalize;
>  
> -	for (i = 0; i < npages; ++i) {
> +	mutex_lock(&dpagemap->folio_split_lock);
> +	for (i = 0; i < npages;) {
> +		unsigned long j;
>  		struct page *page = pfn_to_page(migrate.dst[i]);
> +		unsigned int order;
>  
>  		pages[i] = page;
>  		migrate.dst[i] = migrate_pfn(migrate.dst[i]);
> -		drm_pagemap_get_devmem_page(page, zdd);
> +
> +		if (migrate.src[i] & MIGRATE_PFN_COMPOUND) {
> +			order = HPAGE_PMD_ORDER;
> +
> +			migrate.dst[i] |= MIGRATE_PFN_COMPOUND;
> +
> +			drm_pagemap_get_devmem_page(page, order, zdd);
> +
> +			for (j = 1; j < NR_PAGES(order) && i + j < npages; j++)
> +				migrate.dst[i + j] = 0;
> +
> +		} else {
> +			order = 0;
> +
> +			if (folio_order(page_folio(page)))
> +				migrate_device_split_page(page);
> +
> +			zone_device_page_init(page, 0);
> +			page->zone_device_data = drm_pagemap_zdd_get(zdd);


drm_pagemap_get_devmem_page(page, order, zdd); ?

If so, this part could be moved outside out the if/else clause.

Matt

> +		}
> +
> +		i += NR_PAGES(order);
>  	}
> +	mutex_unlock(&dpagemap->folio_split_lock);
>  
>  	err = ops->copy_to_devmem(pages, pagemap_addr, npages);
>  	if (err)
> @@ -516,6 +542,8 @@ static int drm_pagemap_migrate_populate_ram_pfn(struct vm_area_struct *vas,
>  		page = folio_page(folio, 0);
>  		mpfn[i] = migrate_pfn(page_to_pfn(page));
>  
> +		if (order)
> +			mpfn[i] |= MIGRATE_PFN_COMPOUND;
>  next:
>  		if (page)
>  			addr += page_size(page);
> @@ -617,8 +645,15 @@ int drm_pagemap_evict_to_ram(struct drm_pagemap_devmem *devmem_allocation)
>  	if (err)
>  		goto err_finalize;
>  
> -	for (i = 0; i < npages; ++i)
> +	for (i = 0; i < npages;) {
> +		unsigned int order = 0;
> +
>  		pages[i] = migrate_pfn_to_page(src[i]);
> +		if (pages[i])
> +			order = folio_order(page_folio(pages[i]));
> +
> +		i += NR_PAGES(order);
> +	}
>  
>  	err = ops->copy_to_ram(pages, pagemap_addr, npages);
>  	if (err)
> @@ -671,8 +706,9 @@ static int __drm_pagemap_migrate_to_ram(struct vm_area_struct *vas,
>  	struct migrate_vma migrate = {
>  		.vma		= vas,
>  		.pgmap_owner	= device_private_page_owner,
> -		.flags		= MIGRATE_VMA_SELECT_DEVICE_PRIVATE |
> -		MIGRATE_VMA_SELECT_DEVICE_COHERENT,
> +		.flags		= MIGRATE_VMA_SELECT_DEVICE_PRIVATE
> +				| MIGRATE_VMA_SELECT_DEVICE_COHERENT
> +				| MIGRATE_VMA_SELECT_COMPOUND,
>  		.fault_page	= page,
>  	};
>  	struct drm_pagemap_zdd *zdd;
> @@ -753,8 +789,15 @@ static int __drm_pagemap_migrate_to_ram(struct vm_area_struct *vas,
>  	if (err)
>  		goto err_finalize;
>  
> -	for (i = 0; i < npages; ++i)
> +	for (i = 0; i < npages;) {
> +		unsigned int order = 0;
> +
>  		pages[i] = migrate_pfn_to_page(migrate.src[i]);
> +		if (pages[i])
> +			order = folio_order(page_folio(pages[i]));
> +
> +		i += NR_PAGES(order);
> +	}
>  
>  	err = ops->copy_to_ram(pages, pagemap_addr, npages);
>  	if (err)
> @@ -813,9 +856,26 @@ static vm_fault_t drm_pagemap_migrate_to_ram(struct vm_fault *vmf)
>  	return err ? VM_FAULT_SIGBUS : 0;
>  }
>  
> +static void drm_pagemap_folio_split(struct folio *orig_folio, struct folio *new_folio)
> +{
> +	struct drm_pagemap_zdd *zdd;
> +
> +	if (!new_folio)
> +		return;
> +
> +	new_folio->pgmap = orig_folio->pgmap;
> +	zdd = folio_zone_device_data(orig_folio);
> +	if (folio_order(new_folio))
> +		folio_set_zone_device_data(new_folio, drm_pagemap_zdd_get(zdd));
> +	else
> +		folio_page(new_folio, 0)->zone_device_data =
> +			drm_pagemap_zdd_get(zdd);
> +}
> +
>  static const struct dev_pagemap_ops drm_pagemap_pagemap_ops = {
>  	.folio_free = drm_pagemap_folio_free,
>  	.migrate_to_ram = drm_pagemap_migrate_to_ram,
> +	.folio_split = drm_pagemap_folio_split,
>  };
>  
>  /**
> diff --git a/drivers/gpu/drm/xe/xe_svm.c b/drivers/gpu/drm/xe/xe_svm.c
> index 93550c7c84ac..037c77de2757 100644
> --- a/drivers/gpu/drm/xe/xe_svm.c
> +++ b/drivers/gpu/drm/xe/xe_svm.c
> @@ -4,6 +4,7 @@
>   */
>  
>  #include <drm/drm_drv.h>
> +#include <drm/drm_managed.h>
>  
>  #include "xe_bo.h"
>  #include "xe_exec_queue_types.h"
> @@ -1470,6 +1471,10 @@ int xe_devm_add(struct xe_tile *tile, struct xe_vram_region *vr)
>  	void *addr;
>  	int ret;
>  
> +	ret = drmm_mutex_init(&tile->xe->drm, &vr->dpagemap.folio_split_lock);
> +	if (ret)
> +		return ret;
> +
>  	res = devm_request_free_mem_region(dev, &iomem_resource,
>  					   vr->usable_size);
>  	if (IS_ERR(res)) {
> diff --git a/include/drm/drm_pagemap.h b/include/drm/drm_pagemap.h
> index 3a8d0e1cef43..82b9c0e6392e 100644
> --- a/include/drm/drm_pagemap.h
> +++ b/include/drm/drm_pagemap.h
> @@ -129,11 +129,14 @@ struct drm_pagemap_ops {
>   * struct drm_pagemap: Additional information for a struct dev_pagemap
>   * used for device p2p handshaking.
>   * @ops: The struct drm_pagemap_ops.
> - * @dev: The struct drevice owning the device-private memory.
> + * @dev: The struct device owning the device-private memory.
> + * @folio_split_lock: Lock to protect device folio splitting.
>   */
>  struct drm_pagemap {
>  	const struct drm_pagemap_ops *ops;
>  	struct device *dev;
> +	/* Protect device folio splitting */
> +	struct mutex folio_split_lock;
>  };
>  
>  struct drm_pagemap_devmem;
> -- 
> 2.43.0
>