[PATCH] splice: add support for SPLICE_F_MOVE flag

This enables the caller to migrate pages from one address space page
cache to another.  In buzz word marketing, you can do zero-copy file
copies!

Signed-off-by: Jens Axboe <axboe@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 84 insertions, 37 deletions

diff --git a/fs/splice.c b/fs/splice.c
index efa47c1c4e13..4a026f95884f 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -21,6 +21,7 @@
 #include <linux/pagemap.h>
 #include <linux/pipe_fs_i.h>
 #include <linux/mm_inline.h>
+#include <linux/swap.h>
 
 /*
  * Passed to the actors
@@ -32,11 +33,37 @@ struct splice_desc {
         loff_t pos;                     /* file position */
 };
 
+static int page_cache_pipe_buf_steal(struct pipe_inode_info *info,
+                                     struct pipe_buffer *buf)
+{
+        struct page *page = buf->page;
+
+        WARN_ON(!PageLocked(page));
+        WARN_ON(!PageUptodate(page));
+
+        if (!remove_mapping(page_mapping(page), page))
+                return 1;
+
+        if (PageLRU(page)) {
+                struct zone *zone = page_zone(page);
+
+                spin_lock_irq(&zone->lru_lock);
+                BUG_ON(!PageLRU(page));
+                __ClearPageLRU(page);
+                del_page_from_lru(zone, page);
+                spin_unlock_irq(&zone->lru_lock);
+        }
+
+        buf->stolen = 1;
+        return 0;
+}
+
 static void page_cache_pipe_buf_release(struct pipe_inode_info *info,
                                         struct pipe_buffer *buf)
 {
         page_cache_release(buf->page);
         buf->page = NULL;
+        buf->stolen = 0;
 }
 
 static void *page_cache_pipe_buf_map(struct file *file,
@@ -63,7 +90,8 @@ static void *page_cache_pipe_buf_map(struct file *file,
 static void page_cache_pipe_buf_unmap(struct pipe_inode_info *info,
                                       struct pipe_buffer *buf)
 {
-        unlock_page(buf->page);
+        if (!buf->stolen)
+                unlock_page(buf->page);
         kunmap(buf->page);
 }
 
@@ -72,6 +100,7 @@ static struct pipe_buf_operations page_cache_pipe_buf_ops = {
         .map = page_cache_pipe_buf_map,
         .unmap = page_cache_pipe_buf_unmap,
         .release = page_cache_pipe_buf_release,
+        .steal = page_cache_pipe_buf_steal,
 };
 
 static ssize_t move_to_pipe(struct inode *inode, struct page **pages,
@@ -336,8 +365,8 @@ static int pipe_to_file(struct pipe_inode_info *info, struct pipe_buffer *buf,
         struct address_space *mapping = file->f_mapping;
         unsigned int offset;
         struct page *page;
-        char *src, *dst;
         pgoff_t index;
+        char *src;
         int ret;
 
         /*
@@ -350,40 +379,54 @@ static int pipe_to_file(struct pipe_inode_info *info, struct pipe_buffer *buf,
         index = sd->pos >> PAGE_CACHE_SHIFT;
         offset = sd->pos & ~PAGE_CACHE_MASK;
 
-find_page:
-        ret = -ENOMEM;
-        page = find_or_create_page(mapping, index, mapping_gfp_mask(mapping));
-        if (!page)
-                goto out;
-
         /*
-         * If the page is uptodate, it is also locked. If it isn't
-         * uptodate, we can mark it uptodate if we are filling the
-         * full page. Otherwise we need to read it in first...
+         * reuse buf page, if SPLICE_F_MOVE is set
          */
-        if (!PageUptodate(page)) {
-                if (sd->len < PAGE_CACHE_SIZE) {
-                        ret = mapping->a_ops->readpage(file, page);
-                        if (unlikely(ret))
-                                goto out;
-
-                        lock_page(page);
-
-                        if (!PageUptodate(page)) {
-                                /*
-                                 * page got invalidated, repeat
-                                 */
-                                if (!page->mapping) {
-                                        unlock_page(page);
-                                        page_cache_release(page);
-                                        goto find_page;
+        if (sd->flags & SPLICE_F_MOVE) {
+                if (buf->ops->steal(info, buf))
+                        goto find_page;
+
+                page = buf->page;
+                if (add_to_page_cache_lru(page, mapping, index,
+                                                mapping_gfp_mask(mapping)))
+                        goto find_page;
+        } else {
+find_page:
+                ret = -ENOMEM;
+                page = find_or_create_page(mapping, index,
+                                                mapping_gfp_mask(mapping));
+                if (!page)
+                        goto out;
+
+                /*
+                 * If the page is uptodate, it is also locked. If it isn't
+                 * uptodate, we can mark it uptodate if we are filling the
+                 * full page. Otherwise we need to read it in first...
+                 */
+                if (!PageUptodate(page)) {
+                        if (sd->len < PAGE_CACHE_SIZE) {
+                                ret = mapping->a_ops->readpage(file, page);
+                                if (unlikely(ret))
+                                        goto out;
+
+                                lock_page(page);
+
+                                if (!PageUptodate(page)) {
+                                        /*
+                                         * page got invalidated, repeat
+                                         */
+                                        if (!page->mapping) {
+                                                unlock_page(page);
+                                                page_cache_release(page);
+                                                goto find_page;
+                                        }
+                                        ret = -EIO;
+                                        goto out;
                                 }
-                                ret = -EIO;
-                                goto out;
+                        } else {
+                                WARN_ON(!PageLocked(page));
+                                SetPageUptodate(page);
                         }
-                } else {
-                        WARN_ON(!PageLocked(page));
-                        SetPageUptodate(page);
                 }
         }
 
@@ -391,10 +434,13 @@ find_page:
         if (ret)
                 goto out;
 
-        dst = kmap_atomic(page, KM_USER0);
-        memcpy(dst + offset, src + buf->offset, sd->len);
-        flush_dcache_page(page);
-        kunmap_atomic(dst, KM_USER0);
+        if (!buf->stolen) {
+                char *dst = kmap_atomic(page, KM_USER0);
+
+                memcpy(dst + offset, src + buf->offset, sd->len);
+                flush_dcache_page(page);
+                kunmap_atomic(dst, KM_USER0);
+        }
 
         ret = mapping->a_ops->commit_write(file, page, 0, sd->len);
         if (ret < 0)
@@ -405,7 +451,8 @@ find_page:
 out:
         if (ret < 0)
                 unlock_page(page);
-        page_cache_release(page);
+        if (!buf->stolen)
+                page_cache_release(page);
         buf->ops->unmap(info, buf);
         return ret;
 }