[PATCH] splice: make the read-side do batched page lookups

Use the new find_get_pages_contig() to potentially look up the entire
splice range in one single call. This speeds up generic_file_splice_read()
quite a bit.

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

1 files changed, 65 insertions, 30 deletions

diff --git a/fs/splice.c b/fs/splice.c
index dc205f643090..a46ddd28561e 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -279,7 +279,7 @@ __generic_file_splice_read(struct file *in, loff_t *ppos,
         pgoff_t index, end_index;
         loff_t isize;
         size_t total_len;
-        int error;
+        int error, page_nr;
         struct splice_pipe_desc spd = {
                 .pages = pages,
                 .partial = partial,
@@ -307,39 +307,67 @@ __generic_file_splice_read(struct file *in, loff_t *ppos,
          */
         error = 0;
         total_len = 0;
-        for (spd.nr_pages = 0; spd.nr_pages < nr_pages; spd.nr_pages++, index++) {
-                unsigned int this_len;
 
-                if (!len)
-                        break;
+        /*
+         * Lookup the (hopefully) full range of pages we need.
+         */
+        spd.nr_pages = find_get_pages_contig(mapping, index, nr_pages, pages);
 
+        /*
+         * If find_get_pages_contig() returned fewer pages than we needed,
+         * allocate the rest.
+         */
+        index += spd.nr_pages;
+        while (spd.nr_pages < nr_pages) {
                 /*
-                 * this_len is the max we'll use from this page
-                 */
-                this_len = min_t(unsigned long, len, PAGE_CACHE_SIZE - loff);
-find_page:
-                /*
-                 * lookup the page for this index
+                 * Page could be there, find_get_pages_contig() breaks on
+                 * the first hole.
                  */
                 page = find_get_page(mapping, index);
                 if (!page) {
                         /*
-                         * page didn't exist, allocate one
+                         * page didn't exist, allocate one.
                          */
                         page = page_cache_alloc_cold(mapping);
                         if (!page)
                                 break;
 
                         error = add_to_page_cache_lru(page, mapping, index,
-                                                mapping_gfp_mask(mapping));
+                                              mapping_gfp_mask(mapping));
                         if (unlikely(error)) {
                                 page_cache_release(page);
                                 break;
                         }
-
-                        goto readpage;
+                        /*
+                         * add_to_page_cache() locks the page, unlock it
+                         * to avoid convoluting the logic below even more.
+                         */
+                        unlock_page(page);
                 }
 
+                pages[spd.nr_pages++] = page;
+                index++;
+        }
+
+        /*
+         * Now loop over the map and see if we need to start IO on any
+         * pages, fill in the partial map, etc.
+         */
+        index = *ppos >> PAGE_CACHE_SHIFT;
+        nr_pages = spd.nr_pages;
+        spd.nr_pages = 0;
+        for (page_nr = 0; page_nr < nr_pages; page_nr++) {
+                unsigned int this_len;
+
+                if (!len)
+                        break;
+
+                /*
+                 * this_len is the max we'll use from this page
+                 */
+                this_len = min_t(unsigned long, len, PAGE_CACHE_SIZE - loff);
+                page = pages[page_nr];
+
                 /*
                  * If the page isn't uptodate, we may need to start io on it
                  */
@@ -360,7 +388,6 @@ find_page:
                          */
                         if (!page->mapping) {
                                 unlock_page(page);
-                                page_cache_release(page);
                                 break;
                         }
                         /*
@@ -371,16 +398,20 @@ find_page:
                                 goto fill_it;
                         }
 
-readpage:
                         /*
                          * need to read in the page
                          */
                         error = mapping->a_ops->readpage(in, page);
-
                         if (unlikely(error)) {
-                                page_cache_release(page);
+                                /*
+                                 * We really should re-lookup the page here,
+                                 * but it complicates things a lot. Instead
+                                 * lets just do what we already stored, and
+                                 * we'll get it the next time we are called.
+                                 */
                                 if (error == AOP_TRUNCATED_PAGE)
-                                        goto find_page;
+                                        error = 0;
+
                                 break;
                         }
 
@@ -389,10 +420,8 @@ readpage:
                          */
                         isize = i_size_read(mapping->host);
                         end_index = (isize - 1) >> PAGE_CACHE_SHIFT;
-                        if (unlikely(!isize || index > end_index)) {
-                                page_cache_release(page);
+                        if (unlikely(!isize || index > end_index))
                                 break;
-                        }
 
                         /*
                          * if this is the last page, see if we need to shrink
@@ -400,27 +429,33 @@ readpage:
                          */
                         if (end_index == index) {
                                 loff = PAGE_CACHE_SIZE - (isize & ~PAGE_CACHE_MASK);
-                                if (total_len + loff > isize) {
-                                        page_cache_release(page);
+                                if (total_len + loff > isize)
                                         break;
-                                }
                                 /*
                                  * force quit after adding this page
                                  */
-                                nr_pages = spd.nr_pages;
+                                len = this_len;
                                 this_len = min(this_len, loff);
                                 loff = 0;
                         }
                 }
 fill_it:
-                pages[spd.nr_pages] = page;
-                partial[spd.nr_pages].offset = loff;
-                partial[spd.nr_pages].len = this_len;
+                partial[page_nr].offset = loff;
+                partial[page_nr].len = this_len;
                 len -= this_len;
                 total_len += this_len;
                 loff = 0;
+                spd.nr_pages++;
+                index++;
         }
 
+        /*
+         * Release any pages at the end, if we quit early. 'i' is how far
+         * we got, 'nr_pages' is how many pages are in the map.
+         */
+        while (page_nr < nr_pages)
+                page_cache_release(pages[page_nr++]);
+
         if (spd.nr_pages)
                 return splice_to_pipe(pipe, &spd);