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Date: Fri, 22 Oct 2010 11:29:22 -0400
From: Theodore Ts'o <tytso@....edu>
To: Ext4 Developers List <linux-ext4@...r.kernel.org>
Cc: Theodore Ts'o <tytso@....edu>
Subject: [PATCH 2/6] ext4: simplify ext4_writepage()
The actual code in ext4_writepage() is unnecessarily convoluted.
Simplify it so it is easier to understand, but otherwise logically
equivalent.
Signed-off-by: "Theodore Ts'o" <tytso@....edu>
---
fs/ext4/inode.c | 73 +++++++++++++++++++------------------------------------
1 files changed, 25 insertions(+), 48 deletions(-)
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index c3cc036..58b7008 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -2701,7 +2701,7 @@ static void ext4_end_io_buffer_write(struct buffer_head *bh, int uptodate);
static int ext4_writepage(struct page *page,
struct writeback_control *wbc)
{
- int ret = 0;
+ int ret = 0, commit_write = 0;
loff_t size;
unsigned int len;
struct buffer_head *page_bufs = NULL;
@@ -2714,60 +2714,37 @@ static int ext4_writepage(struct page *page,
else
len = PAGE_CACHE_SIZE;
- if (page_has_buffers(page)) {
- page_bufs = page_buffers(page);
- if (walk_page_buffers(NULL, page_bufs, 0, len, NULL,
- ext4_bh_delay_or_unwritten)) {
- /*
- * We don't want to do block allocation
- * So redirty the page and return
- * We may reach here when we do a journal commit
- * via journal_submit_inode_data_buffers.
- * If we don't have mapping block we just ignore
- * them. We can also reach here via shrink_page_list
- */
+ /*
+ * If the page does not have buffers (for whatever reason),
+ * try to create them using block_prepare_write. If this
+ * fails, redirty the page and move on.
+ */
+ if (!page_buffers(page)) {
+ if (block_prepare_write(page, 0, len,
+ noalloc_get_block_write)) {
+ redirty_page:
redirty_page_for_writepage(wbc, page);
unlock_page(page);
return 0;
}
- } else {
+ commit_write = 1;
+ }
+ page_bufs = page_buffers(page);
+ if (walk_page_buffers(NULL, page_bufs, 0, len, NULL,
+ ext4_bh_delay_or_unwritten)) {
/*
- * The test for page_has_buffers() is subtle:
- * We know the page is dirty but it lost buffers. That means
- * that at some moment in time after write_begin()/write_end()
- * has been called all buffers have been clean and thus they
- * must have been written at least once. So they are all
- * mapped and we can happily proceed with mapping them
- * and writing the page.
- *
- * Try to initialize the buffer_heads and check whether
- * all are mapped and non delay. We don't want to
- * do block allocation here.
+ * We don't want to do block allocation So redirty the
+ * page and return We may reach here when we do a
+ * journal commit via
+ * journal_submit_inode_data_buffers. If we don't
+ * have mapping block we just ignore them. We can also
+ * reach here via shrink_page_list
*/
- ret = block_prepare_write(page, 0, len,
- noalloc_get_block_write);
- if (!ret) {
- page_bufs = page_buffers(page);
- /* check whether all are mapped and non delay */
- if (walk_page_buffers(NULL, page_bufs, 0, len, NULL,
- ext4_bh_delay_or_unwritten)) {
- redirty_page_for_writepage(wbc, page);
- unlock_page(page);
- return 0;
- }
- } else {
- /*
- * We can't do block allocation here
- * so just redity the page and unlock
- * and return
- */
- redirty_page_for_writepage(wbc, page);
- unlock_page(page);
- return 0;
- }
+ goto redirty_page;
+ }
+ if (commit_write)
/* now mark the buffer_heads as dirty and uptodate */
block_commit_write(page, 0, len);
- }
if (PageChecked(page) && ext4_should_journal_data(inode)) {
/*
@@ -2778,7 +2755,7 @@ static int ext4_writepage(struct page *page,
return __ext4_journalled_writepage(page, len);
}
- if (page_bufs && buffer_uninit(page_bufs)) {
+ if (buffer_uninit(page_bufs)) {
ext4_set_bh_endio(page_bufs, inode);
ret = block_write_full_page_endio(page, noalloc_get_block_write,
wbc, ext4_end_io_buffer_write);
--
1.7.1
--
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