Re: Performance of ext4

Mingming
2008-06-24T17:58:39Z

On Tue, 2008-06-24 at 08:37 +0530, Aneesh Kumar K.V wrote:
> 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.
>
>

Right! I will update the patch and merge it to the patch queue.

Mingming
> -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,
> >
> >
> --
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