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SubjectRe: [PATCH 06/11] drm/i915: use vmap in shmem_pin_map
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On 24/09/2020 14:58, Christoph Hellwig wrote:
> shmem_pin_map somewhat awkwardly reimplements vmap using
> alloc_vm_area and manual pte setup. The only practical difference
> is that alloc_vm_area prefeaults the vmalloc area PTEs, which doesn't
> seem to be required here (and could be added to vmap using a flag if
> actually required). Switch to use vmap, and use vfree to free both the
> vmalloc mapping and the page array, as well as dropping the references
> to each page.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
> drivers/gpu/drm/i915/gt/shmem_utils.c | 76 +++++++--------------------
> 1 file changed, 18 insertions(+), 58 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gt/shmem_utils.c b/drivers/gpu/drm/i915/gt/shmem_utils.c
> index 43c7acbdc79dea..f011ea42487e11 100644
> --- a/drivers/gpu/drm/i915/gt/shmem_utils.c
> +++ b/drivers/gpu/drm/i915/gt/shmem_utils.c
> @@ -49,80 +49,40 @@ struct file *shmem_create_from_object(struct drm_i915_gem_object *obj)
> return file;
> }
>
> -static size_t shmem_npte(struct file *file)
> -{
> - return file->f_mapping->host->i_size >> PAGE_SHIFT;
> -}
> -
> -static void __shmem_unpin_map(struct file *file, void *ptr, size_t n_pte)
> -{
> - unsigned long pfn;
> -
> - vunmap(ptr);
> -
> - for (pfn = 0; pfn < n_pte; pfn++) {
> - struct page *page;
> -
> - page = shmem_read_mapping_page_gfp(file->f_mapping, pfn,
> - GFP_KERNEL);
> - if (!WARN_ON(IS_ERR(page))) {
> - put_page(page);
> - put_page(page);
> - }
> - }
> -}
> -
> void *shmem_pin_map(struct file *file)
> {
> - const size_t n_pte = shmem_npte(file);
> - pte_t *stack[32], **ptes, **mem;
> - struct vm_struct *area;
> - unsigned long pfn;
> -
> - mem = stack;
> - if (n_pte > ARRAY_SIZE(stack)) {
> - mem = kvmalloc_array(n_pte, sizeof(*mem), GFP_KERNEL);
> - if (!mem)
> - return NULL;
> - }
> + struct page **pages;
> + size_t n_pages, i;
> + void *vaddr;
>
> - area = alloc_vm_area(n_pte << PAGE_SHIFT, mem);
> - if (!area) {
> - if (mem != stack)
> - kvfree(mem);
> + n_pages = file->f_mapping->host->i_size >> PAGE_SHIFT;
> + pages = kvmalloc_array(n_pages, sizeof(*pages), GFP_KERNEL);
> + if (!pages)
> return NULL;
> - }
>
> - ptes = mem;
> - for (pfn = 0; pfn < n_pte; pfn++) {
> - struct page *page;
> -
> - page = shmem_read_mapping_page_gfp(file->f_mapping, pfn,
> - GFP_KERNEL);
> - if (IS_ERR(page))
> + for (i = 0; i < n_pages; i++) {
> + pages[i] = shmem_read_mapping_page_gfp(file->f_mapping, i,
> + GFP_KERNEL);
> + if (IS_ERR(pages[i]))
> goto err_page;
> -
> - **ptes++ = mk_pte(page, PAGE_KERNEL);
> }
>
> - if (mem != stack)
> - kvfree(mem);
> -
> + vaddr = vmap(pages, n_pages, VM_MAP_PUT_PAGES, PAGE_KERNEL);
> + if (!vaddr)
> + goto err_page;
> mapping_set_unevictable(file->f_mapping);
> - return area->addr;
> -
> + return vaddr;
> err_page:
> - if (mem != stack)
> - kvfree(mem);
> -
> - __shmem_unpin_map(file, area->addr, pfn);
> + while (--i >= 0)
> + put_page(pages[i]);
> + kvfree(pages);
> return NULL;
> }
>
> void shmem_unpin_map(struct file *file, void *ptr)
> {
> mapping_clear_unevictable(file->f_mapping);
> - __shmem_unpin_map(file, ptr, shmem_npte(file));
> + vfree(ptr);
> }
>
> static int __shmem_rw(struct file *file, loff_t off,
>

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

Regards,

Tvrtko

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