Re: Performance of ext4

Mingming
2008-06-24T00:31:26Z

On Mon, 2008-06-23 at 23:15 +0530, Aneesh Kumar K.V wrote:

> I found one place where we fail to update i_disksize. Can you try this
> patch ?
>
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 33f940b..9fa737f 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -1620,7 +1620,10 @@ static int ext4_da_writepage(struct page *page,
> loff_t size;
> unsigned long len;
> handle_t *handle = NULL;
> + ext4_lblk_t block;
> + loff_t disksize;
> struct buffer_head *page_bufs;
> + struct buffer_head *bh, *head;
> struct inode *inode = page->mapping->host;
>
> handle = ext4_journal_current_handle();
> @@ -1662,6 +1665,38 @@ static int ext4_da_writepage(struct page *page,
> else
> ret = block_write_full_page(page, ext4_da_get_block_write, wbc);
>
> + if (ret)
> + return ret;
> + /*
> + * When called via shrink_page_list and if we don't have any unmapped
> + * buffer_head we still could have written some new content in an
> + * already mapped buffer. That means we need to extent i_disksize here
> + */

In this case(when extend the file without need block allocation),
wouldn't make sense to update the i_disksize at write_end() time? So
that the window of i_size different from i_disksize could be much
smaller in this case.

Something like below? (untested)

Signed-off-by: Mingming Cao <cmm@us.ibm.com>
---
fs/ext4/inode.c | 66 ++++++++++++++++++++++++++++++++++++++++++++++++++------
1 file changed, 60 insertions(+), 6 deletions(-)

Index: linux-2.6.26-rc6/fs/ext4/inode.c
===================================================================
--- linux-2.6.26-rc6.orig/fs/ext4/inode.c 2008-06-23 17:28:01.000000000 -0700
+++ linux-2.6.26-rc6/fs/ext4/inode.c 2008-06-23 17:28:10.000000000 -0700
@@ -1573,6 +1573,65 @@ static int ext4_da_write_begin(struct fi
return ret;
}

+static int ext4_bh_unmapped_or_delay(handle_t *handle, struct buffer_head *bh)
+{
+ return !buffer_mapped(bh) || buffer_delay(bh);
+}
+
+static int ext4_da_write_end(struct file *file,
+ struct address_space *mapping,
+ loff_t pos, unsigned len, unsigned copied,
+ struct page *page, void *fsdata)
+{
+ handle_t *handle = NULL;
+ struct inode *inode = mapping->host;
+ int needed_blocks = ext4_writepage_trans_blocks(inode);
+ unsigned from, to;
+ int ret = 0, ret2;
+
+ from = pos & (PAGE_CACHE_SIZE - 1);
+ to = from + len;
+
+ if (ret == 0) {
+ /*
+ * generic_write_end() will run mark_inode_dirty() if i_size
+ * changes. So let's piggyback the i_disksize mark_inode_dirty
+ * into that.
+ */
+ loff_t new_i_size;
+
+ new_i_size = pos + copied;
+ if (new_i_size > EXT4_I(inode)->i_disksize)
+ if (!walk_page_buffers(NULL, page_buffers(page),
+ 0, len, NULL, ext4_bh_unmapped_or_delay)){
+ /*
+ * Updating i_disksize when extending file without
+ * need block allocation
+ */
+ handle = ext4_journal_start(inode, needed_blocks);
+ if (IS_ERR(handle)) {
+ ret = PTR_ERR(handle);
+ return ret;
+ }
+ if (ext4_should_order_data(inode))
+ ret = ext4_jbd2_file_inode(handle, inode);
+
+ EXT4_I(inode)->i_disksize = new_i_size;
+ }
+ ret2 = generic_write_end(file, mapping, pos, len, copied,
+ page, fsdata);
+ copied = ret2;
+ if (ret2 < 0)
+ ret = ret2;
+ }
+ if (handle)
+ ret2 = ext4_journal_stop(handle);
+ if (!ret)
+ ret = ret2;
+
+ return ret ? ret : copied;
+}
+
static void ext4_da_invalidatepage(struct page *page, unsigned long offset)
{
struct buffer_head *head, *bh;
@@ -1682,11 +1741,6 @@ static int bput_one(handle_t *handle, st
return 0;
}

-static int ext4_bh_unmapped_or_delay(handle_t *handle, struct buffer_head *bh)
-{
- return !buffer_mapped(bh) || buffer_delay(bh);
-}
-
/*
* Note that we don't need to start a transaction unless we're journaling data
* because we should have holes filled from ext4_page_mkwrite(). We even don't
@@ -2050,7 +2104,7 @@ static const struct address_space_operat
.writepages = ext4_da_writepages,
.sync_page = block_sync_page,
.write_begin = ext4_da_write_begin,
- .write_end = generic_write_end,
+ .write_end = ext4_da_write_end,
.bmap = ext4_bmap,
.invalidatepage = ext4_da_invalidatepage,
.releasepage = ext4_releasepage,