[PATCH] pipe: introduce ->pin() buffer operation

The ->map() function is really expensive on highmem machines right now,
since it has to use the slower kmap() instead of kmap_atomic(). Splice
rarely needs to access the virtual address of a page, so it's a waste
of time doing it.

Introduce ->pin() to take over the responsibility of making sure the
page data is valid. ->map() is then reduced to just kmap(). That way we
can also share a most of the pipe buffer ops between pipe.c and splice.c

Signed-off-by: Jens Axboe <axboe@suse.de>

3 files changed, 73 insertions, 78 deletions

diff --git a/fs/pipe.c b/fs/pipe.c
index 888f265011bf..d9644fd9cc0d 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -110,14 +110,14 @@ static void anon_pipe_buf_release(struct pipe_inode_info *pipe,
                 page_cache_release(page);
 }
 
-static void * anon_pipe_buf_map(struct file *file, struct pipe_inode_info *pipe,
-                                struct pipe_buffer *buf)
+void *generic_pipe_buf_map(struct pipe_inode_info *pipe,
+                           struct pipe_buffer *buf)
 {
         return kmap(buf->page);
 }
 
-static void anon_pipe_buf_unmap(struct pipe_inode_info *pipe,
-                                struct pipe_buffer *buf)
+void generic_pipe_buf_unmap(struct pipe_inode_info *pipe,
+                            struct pipe_buffer *buf)
 {
         kunmap(buf->page);
 }
@@ -135,19 +135,24 @@ static int anon_pipe_buf_steal(struct pipe_inode_info *pipe,
         return 1;
 }
 
-static void anon_pipe_buf_get(struct pipe_inode_info *info,
-                              struct pipe_buffer *buf)
+void generic_pipe_buf_get(struct pipe_inode_info *info, struct pipe_buffer *buf)
 {
         page_cache_get(buf->page);
 }
 
+int generic_pipe_buf_pin(struct pipe_inode_info *info, struct pipe_buffer *buf)
+{
+        return 0;
+}
+
 static struct pipe_buf_operations anon_pipe_buf_ops = {
         .can_merge = 1,
-        .map = anon_pipe_buf_map,
-        .unmap = anon_pipe_buf_unmap,
+        .map = generic_pipe_buf_map,
+        .unmap = generic_pipe_buf_unmap,
+        .pin = generic_pipe_buf_pin,
         .release = anon_pipe_buf_release,
         .steal = anon_pipe_buf_steal,
-        .get = anon_pipe_buf_get,
+        .get = generic_pipe_buf_get,
 };
 
 static ssize_t
@@ -183,12 +188,14 @@ pipe_readv(struct file *filp, const struct iovec *_iov,
                         if (chars > total_len)
                                 chars = total_len;
 
-                        addr = ops->map(filp, pipe, buf);
-                        if (IS_ERR(addr)) {
+                        error = ops->pin(pipe, buf);
+                        if (error) {
                                 if (!ret)
-                                        ret = PTR_ERR(addr);
+                                        error = ret;
                                 break;
                         }
+
+                        addr = ops->map(pipe, buf);
                         error = pipe_iov_copy_to_user(iov, addr + buf->offset, chars);
                         ops->unmap(pipe, buf);
                         if (unlikely(error)) {
@@ -300,11 +307,11 @@ pipe_writev(struct file *filp, const struct iovec *_iov,
                         void *addr;
                         int error;
 
-                        addr = ops->map(filp, pipe, buf);
-                        if (IS_ERR(addr)) {
-                                error = PTR_ERR(addr);
+                        error = ops->pin(pipe, buf);
+                        if (error)
                                 goto out;
-                        }
+
+                        addr = ops->map(pipe, buf);
                         error = pipe_iov_copy_from_user(offset + addr, iov,
                                                         chars);
                         ops->unmap(pipe, buf);
diff --git a/fs/splice.c b/fs/splice.c
index 1633778f3652..d7538d83c367 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -90,9 +90,8 @@ static void page_cache_pipe_buf_release(struct pipe_inode_info *info,
         buf->flags &= ~PIPE_BUF_FLAG_LRU;
 }
 
-static void *page_cache_pipe_buf_map(struct file *file,
-                                     struct pipe_inode_info *info,
-                                     struct pipe_buffer *buf)
+static int page_cache_pipe_buf_pin(struct pipe_inode_info *info,
+                                   struct pipe_buffer *buf)
 {
         struct page *page = buf->page;
         int err;
@@ -118,49 +117,25 @@ static void *page_cache_pipe_buf_map(struct file *file,
                 }
 
                 /*
-                 * Page is ok afterall, fall through to mapping.
+                 * Page is ok afterall, we are done.
                  */
                 unlock_page(page);
         }
 
-        return kmap(page);
+        return 0;
 error:
         unlock_page(page);
-        return ERR_PTR(err);
-}
-
-static void page_cache_pipe_buf_unmap(struct pipe_inode_info *info,
-                                      struct pipe_buffer *buf)
-{
-        kunmap(buf->page);
-}
-
-static void *user_page_pipe_buf_map(struct file *file,
-                                    struct pipe_inode_info *pipe,
-                                    struct pipe_buffer *buf)
-{
-        return kmap(buf->page);
-}
-
-static void user_page_pipe_buf_unmap(struct pipe_inode_info *pipe,
-                                     struct pipe_buffer *buf)
-{
-        kunmap(buf->page);
-}
-
-static void page_cache_pipe_buf_get(struct pipe_inode_info *info,
-                                    struct pipe_buffer *buf)
-{
-        page_cache_get(buf->page);
+        return err;
 }
 
 static struct pipe_buf_operations page_cache_pipe_buf_ops = {
         .can_merge = 0,
-        .map = page_cache_pipe_buf_map,
-        .unmap = page_cache_pipe_buf_unmap,
+        .map = generic_pipe_buf_map,
+        .unmap = generic_pipe_buf_unmap,
+        .pin = page_cache_pipe_buf_pin,
         .release = page_cache_pipe_buf_release,
         .steal = page_cache_pipe_buf_steal,
-        .get = page_cache_pipe_buf_get,
+        .get = generic_pipe_buf_get,
 };
 
 static int user_page_pipe_buf_steal(struct pipe_inode_info *pipe,
@@ -171,11 +146,12 @@ static int user_page_pipe_buf_steal(struct pipe_inode_info *pipe,
 
 static struct pipe_buf_operations user_page_pipe_buf_ops = {
         .can_merge = 0,
-        .map = user_page_pipe_buf_map,
-        .unmap = user_page_pipe_buf_unmap,
+        .map = generic_pipe_buf_map,
+        .unmap = generic_pipe_buf_unmap,
+        .pin = generic_pipe_buf_pin,
         .release = page_cache_pipe_buf_release,
         .steal = user_page_pipe_buf_steal,
-        .get = page_cache_pipe_buf_get,
+        .get = generic_pipe_buf_get,
 };
 
 /*
@@ -517,26 +493,16 @@ static int pipe_to_sendpage(struct pipe_inode_info *info,
 {
         struct file *file = sd->file;
         loff_t pos = sd->pos;
-        ssize_t ret;
-        void *ptr;
-        int more;
+        int ret, more;
 
-        /*
-         * Sub-optimal, but we are limited by the pipe ->map. We don't
-         * need a kmap'ed buffer here, we just want to make sure we
-         * have the page pinned if the pipe page originates from the
-         * page cache.
-         */
-        ptr = buf->ops->map(file, info, buf);
-        if (IS_ERR(ptr))
-                return PTR_ERR(ptr);
-
-        more = (sd->flags & SPLICE_F_MORE) || sd->len < sd->total_len;
+        ret = buf->ops->pin(info, buf);
+        if (!ret) {
+                more = (sd->flags & SPLICE_F_MORE) || sd->len < sd->total_len;
 
-        ret = file->f_op->sendpage(file, buf->page, buf->offset, sd->len,
-                                   &pos, more);
+                ret = file->f_op->sendpage(file, buf->page, buf->offset,
+                                           sd->len, &pos, more);
+        }
 
-        buf->ops->unmap(info, buf);
         return ret;
 }
 
@@ -569,15 +535,14 @@ static int pipe_to_file(struct pipe_inode_info *info, struct pipe_buffer *buf,
         unsigned int offset, this_len;
         struct page *page;
         pgoff_t index;
-        char *src;
         int ret;
 
         /*
          * make sure the data in this buffer is uptodate
          */
-        src = buf->ops->map(file, info, buf);
-        if (IS_ERR(src))
-                return PTR_ERR(src);
+        ret = buf->ops->pin(info, buf);
+        if (unlikely(ret))
+                return ret;
 
         index = sd->pos >> PAGE_CACHE_SHIFT;
         offset = sd->pos & ~PAGE_CACHE_MASK;
@@ -666,11 +631,16 @@ find_page:
                 goto out;
 
         if (buf->page != page) {
-                char *dst = kmap_atomic(page, KM_USER0);
+                /*
+                 * Careful, ->map() uses KM_USER0!
+                 */
+                char *src = buf->ops->map(info, buf);
+                char *dst = kmap_atomic(page, KM_USER1);
 
                 memcpy(dst + offset, src + buf->offset, this_len);
                 flush_dcache_page(page);
-                kunmap_atomic(dst, KM_USER0);
+                kunmap_atomic(dst, KM_USER1);
+                buf->ops->unmap(info, buf);
         }
 
         ret = mapping->a_ops->commit_write(file, page, offset, offset+this_len);
@@ -690,7 +660,6 @@ out:
         page_cache_release(page);
         unlock_page(page);
 out_nomem:
-        buf->ops->unmap(info, buf);
         return ret;
 }
 
diff --git a/include/linux/pipe_fs_i.h b/include/linux/pipe_fs_i.h
index 3130977fc6ab..b8aae1fc5185 100644
--- a/include/linux/pipe_fs_i.h
+++ b/include/linux/pipe_fs_i.h
@@ -14,10 +14,23 @@ struct pipe_buffer {
         unsigned int flags;
 };
 
+/*
+ * Note on the nesting of these functions:
+ *
+ * ->pin()
+ *      ->steal()
+ *      ...
+ *      ->map()
+ *      ...
+ *      ->unmap()
+ *
+ * That is, ->map() must be called on a pinned buffer, same goes for ->steal().
+ */
 struct pipe_buf_operations {
         int can_merge;
-        void * (*map)(struct file *, struct pipe_inode_info *, struct pipe_buffer *);
+        void * (*map)(struct pipe_inode_info *, struct pipe_buffer *);
         void (*unmap)(struct pipe_inode_info *, struct pipe_buffer *);
+        int (*pin)(struct pipe_inode_info *, struct pipe_buffer *);
         void (*release)(struct pipe_inode_info *, struct pipe_buffer *);
         int (*steal)(struct pipe_inode_info *, struct pipe_buffer *);
         void (*get)(struct pipe_inode_info *, struct pipe_buffer *);
@@ -50,6 +63,12 @@ struct pipe_inode_info * alloc_pipe_info(struct inode * inode);
 void free_pipe_info(struct inode * inode);
 void __free_pipe_info(struct pipe_inode_info *);
 
+/* Generic pipe buffer ops functions */
+void *generic_pipe_buf_map(struct pipe_inode_info *, struct pipe_buffer *);
+void generic_pipe_buf_unmap(struct pipe_inode_info *, struct pipe_buffer *);
+void generic_pipe_buf_get(struct pipe_inode_info *, struct pipe_buffer *);
+int generic_pipe_buf_pin(struct pipe_inode_info *, struct pipe_buffer *);
+
 /*
  * splice is tied to pipes as a transport (at least for now), so we'll just
  * add the splice flags here.