ext4: Use our own write_cache_pages()

Make a copy of write_cache_pages() for the benefit of
ext4_da_writepages().  This allows us to simplify the code some, and
will allow us to further customize the code in future patches.

There are some nasty hacks in write_cache_pages(), which Linus has
(correctly) characterized as vile.  I've just copied it into
write_cache_pages_da(), without trying to clean those bits up lest I
break something in the ext4's delalloc implementation, which is a bit
fragile right now.  This will allow Dave Chinner to clean up
write_cache_pages() in mm/page-writeback.c, without worrying about
breaking ext4.  Eventually write_cache_pages_da() will go away when I
rewrite ext4's delayed allocation and create a general
ext4_writepages() which is used for all of ext4's writeback.  Until
now this is the lowest risk way to clean up the core
write_cache_pages() function.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Cc: Dave Chinner <david@fromorbit.com>

1 files changed, 119 insertions, 22 deletions

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 6aa0442811d..830336d3911 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -2426,17 +2426,6 @@ static int __mpage_da_writepage(struct page *page,
         struct buffer_head *bh, *head;
         sector_t logical;
 
-        if (mpd->io_done) {
-                /*
-                 * Rest of the page in the page_vec
-                 * redirty then and skip then. We will
-                 * try to write them again after
-                 * starting a new transaction
-                 */
-                redirty_page_for_writepage(wbc, page);
-                unlock_page(page);
-                return MPAGE_DA_EXTENT_TAIL;
-        }
         /*
          * Can we merge this page to current extent?
          */
@@ -2831,6 +2820,124 @@ static int ext4_da_writepages_trans_blocks(struct inode *inode)
         return ext4_chunk_trans_blocks(inode, max_blocks);
 }
 
+/*
+ * write_cache_pages_da - walk the list of dirty pages of the given
+ * address space and call the callback function (which usually writes
+ * the pages).
+ *
+ * This is a forked version of write_cache_pages().  Differences:
+ *      Range cyclic is ignored.
+ *      no_nrwrite_index_update is always presumed true
+ */
+static int write_cache_pages_da(struct address_space *mapping,
+                                struct writeback_control *wbc,
+                                struct mpage_da_data *mpd)
+{
+        int ret = 0;
+        int done = 0;
+        struct pagevec pvec;
+        int nr_pages;
+        pgoff_t index;
+        pgoff_t end;            /* Inclusive */
+        long nr_to_write = wbc->nr_to_write;
+
+        pagevec_init(&pvec, 0);
+        index = wbc->range_start >> PAGE_CACHE_SHIFT;
+        end = wbc->range_end >> PAGE_CACHE_SHIFT;
+
+        while (!done && (index <= end)) {
+                int i;
+
+                nr_pages = pagevec_lookup_tag(&pvec, mapping, &index,
+                              PAGECACHE_TAG_DIRTY,
+                              min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1);
+                if (nr_pages == 0)
+                        break;
+
+                for (i = 0; i < nr_pages; i++) {
+                        struct page *page = pvec.pages[i];
+
+                        /*
+                         * At this point, the page may be truncated or
+                         * invalidated (changing page->mapping to NULL), or
+                         * even swizzled back from swapper_space to tmpfs file
+                         * mapping. However, page->index will not change
+                         * because we have a reference on the page.
+                         */
+                        if (page->index > end) {
+                                done = 1;
+                                break;
+                        }
+
+                        lock_page(page);
+
+                        /*
+                         * Page truncated or invalidated. We can freely skip it
+                         * then, even for data integrity operations: the page
+                         * has disappeared concurrently, so there could be no
+                         * real expectation of this data interity operation
+                         * even if there is now a new, dirty page at the same
+                         * pagecache address.
+                         */
+                        if (unlikely(page->mapping != mapping)) {
+continue_unlock:
+                                unlock_page(page);
+                                continue;
+                        }
+
+                        if (!PageDirty(page)) {
+                                /* someone wrote it for us */
+                                goto continue_unlock;
+                        }
+
+                        if (PageWriteback(page)) {
+                                if (wbc->sync_mode != WB_SYNC_NONE)
+                                        wait_on_page_writeback(page);
+                                else
+                                        goto continue_unlock;
+                        }
+
+                        BUG_ON(PageWriteback(page));
+                        if (!clear_page_dirty_for_io(page))
+                                goto continue_unlock;
+
+                        ret = __mpage_da_writepage(page, wbc, mpd);
+                        if (unlikely(ret)) {
+                                if (ret == AOP_WRITEPAGE_ACTIVATE) {
+                                        unlock_page(page);
+                                        ret = 0;
+                                } else {
+                                        done = 1;
+                                        break;
+                                }
+                        }
+
+                        if (nr_to_write > 0) {
+                                nr_to_write--;
+                                if (nr_to_write == 0 &&
+                                    wbc->sync_mode == WB_SYNC_NONE) {
+                                        /*
+                                         * We stop writing back only if we are
+                                         * not doing integrity sync. In case of
+                                         * integrity sync we have to keep going
+                                         * because someone may be concurrently
+                                         * dirtying pages, and we might have
+                                         * synced a lot of newly appeared dirty
+                                         * pages, but have not synced all of the
+                                         * old dirty pages.
+                                         */
+                                        done = 1;
+                                        break;
+                                }
+                        }
+                }
+                pagevec_release(&pvec);
+                cond_resched();
+        }
+        return ret;
+}
+
+
 static int ext4_da_writepages(struct address_space *mapping,
                               struct writeback_control *wbc)
 {
@@ -2839,7 +2946,6 @@ static int ext4_da_writepages(struct address_space *mapping,
         handle_t *handle = NULL;
         struct mpage_da_data mpd;
         struct inode *inode = mapping->host;
-        int no_nrwrite_index_update;
         int pages_written = 0;
         long pages_skipped;
         unsigned int max_pages;
@@ -2919,12 +3025,6 @@ static int ext4_da_writepages(struct address_space *mapping,
         mpd.wbc = wbc;
         mpd.inode = mapping->host;
 
-        /*
-         * we don't want write_cache_pages to update
-         * nr_to_write and writeback_index
-         */
-        no_nrwrite_index_update = wbc->no_nrwrite_index_update;
-        wbc->no_nrwrite_index_update = 1;
         pages_skipped = wbc->pages_skipped;
 
 retry:
@@ -2966,8 +3066,7 @@ retry:
                 mpd.io_done = 0;
                 mpd.pages_written = 0;
                 mpd.retval = 0;
-                ret = write_cache_pages(mapping, wbc, __mpage_da_writepage,
-                                        &mpd);
+                ret = write_cache_pages_da(mapping, wbc, &mpd);
                 /*
                  * If we have a contiguous extent of pages and we
                  * haven't done the I/O yet, map the blocks and submit
@@ -3033,8 +3132,6 @@ retry:
                 mapping->writeback_index = index;
 
 out_writepages:
-        if (!no_nrwrite_index_update)
-                wbc->no_nrwrite_index_update = 0;
         wbc->nr_to_write -= nr_to_writebump;
         wbc->range_start = range_start;
         trace_ext4_da_writepages_result(inode, wbc, ret, pages_written);