Re: [PATCH] udmabuf: Add support for mapping hugepages (v3)

I see the number of entries in the list often exceeds list_limit currently hardcoded to 1024 for full HD scanout resource (== 1920*1080*4 bytes). Can we include a change to increase it to something like 4096 or higher in this patch?

On Fri, Jun 04, 2021 at 01:59:39PM -0700, Vivek Kasireddy wrote:

If the VMM's (Qemu) memory backend is backed up by memfd + Hugepages (hugetlbfs and not THP), we have to first find the hugepage(s) where the Guest allocations are located and then extract the regular 4k sized subpages from them.

v2: Ensure that the subpage and hugepage offsets are calculated correctly when the range of subpage allocations cuts across multiple hugepages.

v3: Instead of repeatedly looking up the hugepage for each subpage, only do it when the subpage allocation crosses over into a different hugepage. (suggested by Gerd and DW)

Cc: Gerd Hoffmann kraxel@redhat.com Signed-off-by: Vivek Kasireddy vivek.kasireddy@intel.com Signed-off-by: Dongwon Kim dongwon.kim@intel.com

---

drivers/dma-buf/udmabuf.c | 51 +++++++++++++++++++++++++++++++++------ 1 file changed, 44 insertions(+), 7 deletions(-)

diff --git a/drivers/dma-buf/udmabuf.c b/drivers/dma-buf/udmabuf.c index db732f71e59a..2e02bbfe30fd 100644 --- a/drivers/dma-buf/udmabuf.c +++ b/drivers/dma-buf/udmabuf.c @@ -11,6 +11,7 @@ #include <linux/shmem_fs.h> #include <linux/slab.h> #include <linux/udmabuf.h> +#include <linux/hugetlb.h>

static const u32 list_limit = 1024; /* udmabuf_create_list->count limit */ static const size_t size_limit_mb = 64; /* total dmabuf size, in megabytes */ @@ -163,7 +164,9 @@ static long udmabuf_create(struct miscdevice *device, struct udmabuf *ubuf; struct dma_buf *buf; pgoff_t pgoff, pgcnt, pgidx, pgbuf = 0, pglimit;

• struct page *page;

• struct page *page, *hpage = NULL;
• pgoff_t subpgoff, maxsubpgs;
• struct hstate *hpstate; int seals, ret = -EINVAL; u32 i, flags;

@@ -194,7 +197,8 @@ static long udmabuf_create(struct miscdevice *device, memfd = fget(list[i].memfd); if (!memfd) goto err;

• if (!shmem_mapping(file_inode(memfd)->i_mapping))
  

• if (!shmem_mapping(file_inode(memfd)->i_mapping) &&
  

•     !is_file_hugepages(memfd))
  goto err;
  

  seals = memfd_fcntl(memfd, F_GET_SEALS, 0); if (seals == -EINVAL)

@@ -205,17 +209,50 @@ static long udmabuf_create(struct miscdevice *device, goto err; pgoff = list[i].offset >> PAGE_SHIFT; pgcnt = list[i].size >> PAGE_SHIFT;

• if (is_file_hugepages(memfd)) {
  

• 	hpstate = hstate_file(memfd);
  

• 	pgoff = list[i].offset >> huge_page_shift(hpstate);
  

• 	subpgoff = (list[i].offset &
  

• 		    ~huge_page_mask(hpstate)) >> PAGE_SHIFT;
  

• 	maxsubpgs = huge_page_size(hpstate) >> PAGE_SHIFT;
  

• }
  

  for (pgidx = 0; pgidx < pgcnt; pgidx++) {

• 	page = shmem_read_mapping_page(
  

• 		file_inode(memfd)->i_mapping, pgoff + pgidx);
  

• 	if (IS_ERR(page)) {
  

• 		ret = PTR_ERR(page);
  

• 		goto err;
  

• 	if (is_file_hugepages(memfd)) {
  

• 		if (!hpage) {
  

• 			hpage = find_get_page_flags(
  

• 				file_inode(memfd)->i_mapping,
  

• 				pgoff, FGP_ACCESSED);
  

• 			if (IS_ERR(hpage)) {
  

• 				ret = PTR_ERR(hpage);
  

• 				goto err;
  

• 			}
  

• 		}
  

• 		page = hpage + subpgoff;
  

• 		get_page(page);
  

• 		subpgoff++;
  

• 		if (subpgoff == maxsubpgs) {
  

• 			put_page(hpage);
  

• 			hpage = NULL;
  

• 			subpgoff = 0;
  

• 			pgoff++;
  

• 		}
  

• 	} else {
  

• 		page = shmem_read_mapping_page(
  

• 			file_inode(memfd)->i_mapping,
  

• 			pgoff + pgidx);
  

• 		if (IS_ERR(page)) {
  

• 			ret = PTR_ERR(page);
  

• 			goto err;
  

• 		}
  }
  ubuf->pages[pgbuf++] = page;
  

  } fput(memfd); memfd = NULL;

• if (hpage) {
  

• 	put_page(hpage);
  

• 	hpage = NULL;
  

• }
  

  }

  exp_info.ops = &udmabuf_ops;

-- 2.30.2