Re: [PATCH] Re-dirty pages on I/O error

Christoph Hellwig
2008-09-11T10:32:18Z

On Thu, Sep 11, 2008 at 06:37:33PM +1000, Lachlan McIlroy wrote:
> If we get an error in xfs_page_state_convert() - and it's not EAGAIN - then
> we throw away the dirty page without converting the delayed allocation. This
> leaves delayed allocations that can never be removed and confuses code that
> expects a flush of the file to clear them. We need to re-dirty the page on
> error so we can try again later or report that the flush failed.
>
> --- a/fs/xfs/linux-2.6/xfs_aops.c 2008-09-11 16:32:11.000000000 +1000
> +++ b/fs/xfs/linux-2.6/xfs_aops.c 2008-09-11 15:44:09.000000000 +1000
> @@ -1147,16 +1147,6 @@ error:
> if (iohead)
> xfs_cancel_ioend(iohead);
>
> - /*
> - * If it's delalloc and we have nowhere to put it,
> - * throw it away, unless the lower layers told
> - * us to try again.
> - */
> - if (err != -EAGAIN) {
> - if (!unmapped)
> - block_invalidatepage(page, 0);
> - ClearPageUptodate(page);
> - }

While this always looked fishy to me we it needs a good explanation to
kill this. I try to remember why Steve did it this way long time ago.

> @@ -1216,8 +1206,11 @@ xfs_vm_writepage(
> * then mark the page dirty again and leave the page
> * as is.
> */
> - if (current_test_flags(PF_FSTRANS) && need_trans)
> - goto out_fail;
> + if (current_test_flags(PF_FSTRANS) && need_trans) {
> + redirty_page_for_writepage(wbc, page);
> + unlock_page(page);
> + return -EAGAIN;

The redirty, unlock, return sequence is duplicated after your
patch, I think we should still keep the out_fail goto. Also returning
-EGAIN from ->writepage is wrong. The return values goes through
handle_write_error and mapping_set_error into the return value of e.g.
msync. If you look at all similar writepage implementation they only
return a negative error for a real error condition and simply return 0
when just redirtying it due to transaction constraints or when trylocks
fail.