Re: Performance of ext4

Aneesh Kumar K.V
2008-06-24T03:07:59Z

On Mon, Jun 23, 2008 at 05:31:32PM -0700, Mingming wrote:
>
> 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)

In this case you will have to start a transaction in write_begin . With
the below code transaction is started inside page_lock. Also I don't
think we need needed_blocks credit just 1 should be enough because we
are not doing any block allocation here. We just need to update the
inode block.

-aneesh

>
> 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,
>
>