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Subject[14/23] ext4: Use our own write_cache_pages()
2.6.27-stable review patch.  If anyone has any objections, please let us know.

------------------


From: Theodore Ts'o <tytso@mit.edu>

commit 8e48dcfbd7c0892b4cfd064d682cc4c95a29df32 upstream.

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>
[dev@jaysonking.com: Dropped the hunks which reverted the use of no_nrwrite_index_update, since those lines weren't ever created on 2.6.27.y]
[dev@jaysonking.com: Copied from 2.6.27.y's version of write_cache_pages(), plus the changes to it from patch "vfs: Add no_nrwrite_index_update writeback control flag"]
Signed-off-by: Jayson R. King <dev@jaysonking.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
fs/ext4/inode.c | 144 +++++++++++++++++++++++++++++++++++++++++++++++++++-----
1 file changed, 132 insertions(+), 12 deletions(-)

--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -2059,17 +2059,6 @@ static int __mpage_da_writepage(struct p
struct buffer_head *bh, *head, fake;
sector_t logical;

- if (mpd->io_done) {
- /*
- * Rest of the page in the page_vec
- * redirty then and skip then. We will
- * try to 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?
*/
@@ -2160,6 +2149,137 @@ static int __mpage_da_writepage(struct p
}

/*
+ * 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)
+{
+ struct backing_dev_info *bdi = mapping->backing_dev_info;
+ 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;
+
+ if (wbc->nonblocking && bdi_write_congested(bdi)) {
+ wbc->encountered_congestion = 1;
+ return 0;
+ }
+
+ 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;
+ }
+ }
+
+ if (wbc->nonblocking && bdi_write_congested(bdi)) {
+ wbc->encountered_congestion = 1;
+ done = 1;
+ break;
+ }
+ }
+ pagevec_release(&pvec);
+ cond_resched();
+ }
+ return ret;
+}
+
+
+/*
* mpage_da_writepages - walk the list of dirty pages of the given
* address space, allocates non-allocated blocks, maps newly-allocated
* blocks to existing bhs and issue IO them
@@ -2192,7 +2312,7 @@ static int mpage_da_writepages(struct ad

to_write = wbc->nr_to_write;

- ret = write_cache_pages(mapping, wbc, __mpage_da_writepage, mpd);
+ ret = write_cache_pages_da(mapping, wbc, mpd);

/*
* Handle last extent of pages



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