tcm_vhost: Optimize gup in vhost_scsi_map_to_sgl

We can get all the pages in one time instead of calling
gup N times.

Signed-off-by: Asias He <asias@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

1 files changed, 30 insertions, 24 deletions

diff --git a/drivers/vhost/tcm_vhost.c b/drivers/vhost/tcm_vhost.c
index 62058d7a562f..704e4f674776 100644
--- a/drivers/vhost/tcm_vhost.c
+++ b/drivers/vhost/tcm_vhost.c
@@ -430,40 +430,47 @@ static struct tcm_vhost_cmd *vhost_scsi_allocate_cmd(
  * Returns the number of scatterlist entries used or -errno on error.
  */
 static int vhost_scsi_map_to_sgl(struct scatterlist *sgl,
-        unsigned int sgl_count, void __user *ptr, size_t len, int write)
+        unsigned int sgl_count, struct iovec *iov, int write)
 {
+        unsigned int npages = 0, pages_nr, offset, nbytes;
         struct scatterlist *sg = sgl;
-        unsigned int npages = 0;
-        int ret;
+        void __user *ptr = iov->iov_base;
+        size_t len = iov->iov_len;
+        struct page **pages;
+        int ret, i;
 
-        while (len > 0) {
-                struct page *page;
-                unsigned int offset = (uintptr_t)ptr & ~PAGE_MASK;
-                unsigned int nbytes = min_t(unsigned int,
-                                PAGE_SIZE - offset, len);
+        pages_nr = iov_num_pages(iov);
+        if (pages_nr > sgl_count)
+                return -ENOBUFS;
 
-                if (npages == sgl_count) {
-                        ret = -ENOBUFS;
-                        goto err;
-                }
+        pages = kmalloc(pages_nr * sizeof(struct page *), GFP_KERNEL);
+        if (!pages)
+                return -ENOMEM;
 
-                ret = get_user_pages_fast((unsigned long)ptr, 1, write, &page);
-                BUG_ON(ret == 0); /* we should either get our page or fail */
-                if (ret < 0)
-                        goto err;
+        ret = get_user_pages_fast((unsigned long)ptr, pages_nr, write, pages);
+        /* No pages were pinned */
+        if (ret < 0)
+                goto out;
+        /* Less pages pinned than wanted */
+        if (ret != pages_nr) {
+                for (i = 0; i < ret; i++)
+                        put_page(pages[i]);
+                ret = -EFAULT;
+                goto out;
+        }
 
-                sg_set_page(sg, page, nbytes, offset);
+        while (len > 0) {
+                offset = (uintptr_t)ptr & ~PAGE_MASK;
+                nbytes = min_t(unsigned int, PAGE_SIZE - offset, len);
+                sg_set_page(sg, pages[npages], nbytes, offset);
                 ptr += nbytes;
                 len -= nbytes;
                 sg++;
                 npages++;
         }
-        return npages;
 
-err:
-        /* Put pages that we hold */
-        for (sg = sgl; sg != &sgl[npages]; sg++)
-                put_page(sg_page(sg));
+out:
+        kfree(pages);
         return ret;
 }
 
@@ -496,8 +503,7 @@ static int vhost_scsi_map_iov_to_sgl(struct tcm_vhost_cmd *tv_cmd,
 
         pr_debug("Mapping %u iovecs for %u pages\n", niov, sgl_count);
         for (i = 0; i < niov; i++) {
-                ret = vhost_scsi_map_to_sgl(sg, sgl_count, iov[i].iov_base,
-                                        iov[i].iov_len, write);
+                ret = vhost_scsi_map_to_sgl(sg, sgl_count, &iov[i], write);
                 if (ret < 0) {
                         for (i = 0; i < tv_cmd->tvc_sgl_count; i++)
                                 put_page(sg_page(&tv_cmd->tvc_sgl[i]));