consolidate generic_writepages and mpage_writepages

Clean up massive code duplication between mpage_writepages() and
generic_writepages().

The new generic function, write_cache_pages() takes a function pointer
argument, which will be called for each page to be written.

Maybe cifs_writepages() too can use this infrastructure, but I'm not
touching that with a ten-foot pole.

The upcoming page writeback support in fuse will also want this.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Acked-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

4 files changed, 93 insertions, 151 deletions

diff --git a/fs/mpage.c b/fs/mpage.c
index 0fb914fc2ee0..c1698f2291aa 100644
--- a/fs/mpage.c
+++ b/fs/mpage.c
@@ -454,11 +454,18 @@ EXPORT_SYMBOL(mpage_readpage);
  * written, so it can intelligently allocate a suitably-sized BIO.  For now,
  * just allocate full-size (16-page) BIOs.
  */
-static struct bio *
-__mpage_writepage(struct bio *bio, struct page *page, get_block_t get_block,
-        sector_t *last_block_in_bio, int *ret, struct writeback_control *wbc,
-        writepage_t writepage_fn)
+struct mpage_data {
+        struct bio *bio;
+        sector_t last_block_in_bio;
+        get_block_t *get_block;
+        unsigned use_writepage;
+};
+
+static int __mpage_writepage(struct page *page, struct writeback_control *wbc,
+                             void *data)
 {
+        struct mpage_data *mpd = data;
+        struct bio *bio = mpd->bio;
         struct address_space *mapping = page->mapping;
         struct inode *inode = page->mapping->host;
         const unsigned blkbits = inode->i_blkbits;
@@ -476,6 +483,7 @@ __mpage_writepage(struct bio *bio, struct page *page, get_block_t get_block,
         int length;
         struct buffer_head map_bh;
         loff_t i_size = i_size_read(inode);
+        int ret = 0;
 
         if (page_has_buffers(page)) {
                 struct buffer_head *head = page_buffers(page);
@@ -538,7 +546,7 @@ __mpage_writepage(struct bio *bio, struct page *page, get_block_t get_block,
 
                 map_bh.b_state = 0;
                 map_bh.b_size = 1 << blkbits;
-                if (get_block(inode, block_in_file, &map_bh, 1))
+                if (mpd->get_block(inode, block_in_file, &map_bh, 1))
                         goto confused;
                 if (buffer_new(&map_bh))
                         unmap_underlying_metadata(map_bh.b_bdev,
@@ -584,7 +592,7 @@ page_is_mapped:
         /*
          * This page will go to BIO.  Do we need to send this BIO off first?
          */
-        if (bio && *last_block_in_bio != blocks[0] - 1)
+        if (bio && mpd->last_block_in_bio != blocks[0] - 1)
                 bio = mpage_bio_submit(WRITE, bio);
 
 alloc_new:
@@ -641,7 +649,7 @@ alloc_new:
                                         boundary_block, 1 << blkbits);
                 }
         } else {
-                *last_block_in_bio = blocks[blocks_per_page - 1];
+                mpd->last_block_in_bio = blocks[blocks_per_page - 1];
         }
         goto out;
 
@@ -649,18 +657,19 @@ confused:
         if (bio)
                 bio = mpage_bio_submit(WRITE, bio);
 
-        if (writepage_fn) {
-                *ret = (*writepage_fn)(page, wbc);
+        if (mpd->use_writepage) {
+                ret = mapping->a_ops->writepage(page, wbc);
         } else {
-                *ret = -EAGAIN;
+                ret = -EAGAIN;
                 goto out;
         }
         /*
          * The caller has a ref on the inode, so *mapping is stable
          */
-        mapping_set_error(mapping, *ret);
+        mapping_set_error(mapping, ret);
 out:
-        return bio;
+        mpd->bio = bio;
+        return ret;
 }
 
 /**
@@ -683,120 +692,27 @@ out:
  * the call was made get new I/O started against them.  If wbc->sync_mode is
  * WB_SYNC_ALL then we were called for data integrity and we must wait for
  * existing IO to complete.
- *
- * If you fix this you should check generic_writepages() also!
  */
 int
 mpage_writepages(struct address_space *mapping,
                 struct writeback_control *wbc, get_block_t get_block)
 {
-        struct backing_dev_info *bdi = mapping->backing_dev_info;
-        struct bio *bio = NULL;
-        sector_t last_block_in_bio = 0;
-        int ret = 0;
-        int done = 0;
-        int (*writepage)(struct page *page, struct writeback_control *wbc);
-        struct pagevec pvec;
-        int nr_pages;
-        pgoff_t index;
-        pgoff_t end;            /* Inclusive */
-        int scanned = 0;
-        int range_whole = 0;
-
-        if (wbc->nonblocking && bdi_write_congested(bdi)) {
-                wbc->encountered_congestion = 1;
-                return 0;
-        }
-
-        writepage = NULL;
-        if (get_block == NULL)
-                writepage = mapping->a_ops->writepage;
-
-        pagevec_init(&pvec, 0);
-        if (wbc->range_cyclic) {
-                index = mapping->writeback_index; /* Start from prev offset */
-                end = -1;
-        } else {
-                index = wbc->range_start >> PAGE_CACHE_SHIFT;
-                end = wbc->range_end >> PAGE_CACHE_SHIFT;
-                if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
-                        range_whole = 1;
-                scanned = 1;
+        int ret;
+
+        if (!get_block)
+                ret = generic_writepages(mapping, wbc);
+        else {
+                struct mpage_data mpd = {
+                        .bio = NULL,
+                        .last_block_in_bio = 0,
+                        .get_block = get_block,
+                        .use_writepage = 1,
+                };
+
+                ret = write_cache_pages(mapping, wbc, __mpage_writepage, &mpd);
+                if (mpd.bio)
+                        mpage_bio_submit(WRITE, mpd.bio);
         }
-retry:
-        while (!done && (index <= end) &&
-                        (nr_pages = pagevec_lookup_tag(&pvec, mapping, &index,
-                        PAGECACHE_TAG_DIRTY,
-                        min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1))) {
-                unsigned i;
-
-                scanned = 1;
-                for (i = 0; i < nr_pages; i++) {
-                        struct page *page = pvec.pages[i];
-
-                        /*
-                         * At this point we hold neither mapping->tree_lock nor
-                         * lock on the page itself: the page may be truncated or
-                         * invalidated (changing page->mapping to NULL), or even
-                         * swizzled back from swapper_space to tmpfs file
-                         * mapping
-                         */
-
-                        lock_page(page);
-
-                        if (unlikely(page->mapping != mapping)) {
-                                unlock_page(page);
-                                continue;
-                        }
-
-                        if (!wbc->range_cyclic && page->index > end) {
-                                done = 1;
-                                unlock_page(page);
-                                continue;
-                        }
-
-                        if (wbc->sync_mode != WB_SYNC_NONE)
-                                wait_on_page_writeback(page);
-
-                        if (PageWriteback(page) ||
-                                        !clear_page_dirty_for_io(page)) {
-                                unlock_page(page);
-                                continue;
-                        }
-
-                        if (writepage) {
-                                ret = (*writepage)(page, wbc);
-                                mapping_set_error(mapping, ret);
-                        } else {
-                                bio = __mpage_writepage(bio, page, get_block,
-                                                &last_block_in_bio, &ret, wbc,
-                                                page->mapping->a_ops->writepage);
-                        }
-                        if (unlikely(ret == AOP_WRITEPAGE_ACTIVATE))
-                                unlock_page(page);
-                        if (ret || (--(wbc->nr_to_write) <= 0))
-                                done = 1;
-                        if (wbc->nonblocking && bdi_write_congested(bdi)) {
-                                wbc->encountered_congestion = 1;
-                                done = 1;
-                        }
-                }
-                pagevec_release(&pvec);
-                cond_resched();
-        }
-        if (!scanned && !done) {
-                /*
-                 * We hit the last page and there is more work to be done: wrap
-                 * back to the start of the file
-                 */
-                scanned = 1;
-                index = 0;
-                goto retry;
-        }
-        if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
-                mapping->writeback_index = index;
-        if (bio)
-                mpage_bio_submit(WRITE, bio);
         return ret;
 }
 EXPORT_SYMBOL(mpage_writepages);
@@ -804,15 +720,15 @@ EXPORT_SYMBOL(mpage_writepages);
 int mpage_writepage(struct page *page, get_block_t get_block,
         struct writeback_control *wbc)
 {
-        int ret = 0;
-        struct bio *bio;
-        sector_t last_block_in_bio = 0;
-
-        bio = __mpage_writepage(NULL, page, get_block,
-                        &last_block_in_bio, &ret, wbc, NULL);
-        if (bio)
-                mpage_bio_submit(WRITE, bio);
-
+        struct mpage_data mpd = {
+                .bio = NULL,
+                .last_block_in_bio = 0,
+                .get_block = get_block,
+                .use_writepage = 0,
+        };
+        int ret = __mpage_writepage(page, wbc, &mpd);
+        if (mpd.bio)
+                mpage_bio_submit(WRITE, mpd.bio);
         return ret;
 }
 EXPORT_SYMBOL(mpage_writepage);
diff --git a/include/linux/mpage.h b/include/linux/mpage.h
index cc5fb75af78a..068a0c9946af 100644
--- a/include/linux/mpage.h
+++ b/include/linux/mpage.h
@@ -12,7 +12,6 @@
 #ifdef CONFIG_BLOCK
 
 struct writeback_control;
-typedef int (writepage_t)(struct page *page, struct writeback_control *wbc);
 
 int mpage_readpages(struct address_space *mapping, struct list_head *pages,
                                 unsigned nr_pages, get_block_t get_block);
diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index daa6c125f66e..050915b59576 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -111,9 +111,15 @@ balance_dirty_pages_ratelimited(struct address_space *mapping)
         balance_dirty_pages_ratelimited_nr(mapping, 1);
 }
 
+typedef int (*writepage_t)(struct page *page, struct writeback_control *wbc,
+                                void *data);
+
 int pdflush_operation(void (*fn)(unsigned long), unsigned long arg0);
-extern int generic_writepages(struct address_space *mapping,
-                              struct writeback_control *wbc);
+int generic_writepages(struct address_space *mapping,
+                       struct writeback_control *wbc);
+int write_cache_pages(struct address_space *mapping,
+                      struct writeback_control *wbc, writepage_t writepage,
+                      void *data);
 int do_writepages(struct address_space *mapping, struct writeback_control *wbc);
 int sync_page_range(struct inode *inode, struct address_space *mapping,
                         loff_t pos, loff_t count);
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 63cd88840eb2..eec1481ba44f 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -588,31 +588,27 @@ void __init page_writeback_init(void)
 }
 
 /**
- * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
+ * write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
  * @mapping: address space structure to write
  * @wbc: subtract the number of written pages from *@wbc->nr_to_write
+ * @writepage: function called for each page
+ * @data: data passed to writepage function
  *
- * This is a library function, which implements the writepages()
- * address_space_operation.
- *
- * If a page is already under I/O, generic_writepages() skips it, even
+ * If a page is already under I/O, write_cache_pages() skips it, even
  * if it's dirty.  This is desirable behaviour for memory-cleaning writeback,
  * but it is INCORRECT for data-integrity system calls such as fsync().  fsync()
  * and msync() need to guarantee that all the data which was dirty at the time
  * the call was made get new I/O started against them.  If wbc->sync_mode is
  * WB_SYNC_ALL then we were called for data integrity and we must wait for
  * existing IO to complete.
- *
- * Derived from mpage_writepages() - if you fix this you should check that
- * also!
  */
-int generic_writepages(struct address_space *mapping,
-                       struct writeback_control *wbc)
+int write_cache_pages(struct address_space *mapping,
+                      struct writeback_control *wbc, writepage_t writepage,
+                      void *data)
 {
         struct backing_dev_info *bdi = mapping->backing_dev_info;
         int ret = 0;
         int done = 0;
-        int (*writepage)(struct page *page, struct writeback_control *wbc);
         struct pagevec pvec;
         int nr_pages;
         pgoff_t index;
@@ -625,12 +621,6 @@ int generic_writepages(struct address_space *mapping,
                 return 0;
         }
 
-        writepage = mapping->a_ops->writepage;
-
-        /* deal with chardevs and other special file */
-        if (!writepage)
-                return 0;
-
         pagevec_init(&pvec, 0);
         if (wbc->range_cyclic) {
                 index = mapping->writeback_index; /* Start from prev offset */
@@ -682,8 +672,7 @@ retry:
                                 continue;
                         }
 
-                        ret = (*writepage)(page, wbc);
-                        mapping_set_error(mapping, ret);
+                        ret = (*writepage)(page, wbc, data);
 
                         if (unlikely(ret == AOP_WRITEPAGE_ACTIVATE))
                                 unlock_page(page);
@@ -710,6 +699,38 @@ retry:
                 mapping->writeback_index = index;
         return ret;
 }
+EXPORT_SYMBOL(write_cache_pages);
+
+/*
+ * Function used by generic_writepages to call the real writepage
+ * function and set the mapping flags on error
+ */
+static int __writepage(struct page *page, struct writeback_control *wbc,
+                       void *data)
+{
+        struct address_space *mapping = data;
+        int ret = mapping->a_ops->writepage(page, wbc);
+        mapping_set_error(mapping, ret);
+        return ret;
+}
+
+/**
+ * generic_writepages - walk the list of dirty pages of the given address space and writepage() all of them.
+ * @mapping: address space structure to write
+ * @wbc: subtract the number of written pages from *@wbc->nr_to_write
+ *
+ * This is a library function, which implements the writepages()
+ * address_space_operation.
+ */
+int generic_writepages(struct address_space *mapping,
+                       struct writeback_control *wbc)
+{
+        /* deal with chardevs and other special file */
+        if (!mapping->a_ops->writepage)
+                return 0;
+
+        return write_cache_pages(mapping, wbc, __writepage, mapping);
+}
 
 EXPORT_SYMBOL(generic_writepages);