On Mon, Feb 08, 2016 at 04:44:15PM +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner@xxxxxxxxxx>
>
> xfs_vm_writepages() calls generic_writepages to writeback a range of
> a file, but then xfs_vm_writepage() clusters pages itself as it does
> not have any context it can pass between->writepage calls from
> __write_cache_pages().
>
> Introduce a writeback context for xfs_vm_writepages() and call
> __write_cache_pages directly with our own writepage callback so that
> we can pass that context to each writepage invocation. This
> encapsulates the current mapping, whether it is valid or not, the
> current ioend and it's IO type and the ioend chain being built.
>
> This requires us to move the ioend submission up to the level where
> the writepage context is declared. This does mean we do not submit
> IO until we packaged the entire writeback range, but with the block
> plugging in the writepages call this is the way IO is submitted,
> anyway.
>
> It also means that we need to handle discontiguous page ranges. If
> the pages sent down by write_cache_pages to the writepage callback
> are discontiguous, we need to detect this and put each discontiguous
> page range into individual ioends. This is needed to ensure that the
> ioend accurately represents the range of the file that it covers so
> that file size updates during IO completion set the size correctly.
> Failure to take into account the discontiguous ranges results in
> files being too small when writeback patterns are non-sequential.
>
> Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
> ---
> fs/xfs/xfs_aops.c | 277 ++++++++++++++++++++++++++++--------------------------
> 1 file changed, 146 insertions(+), 131 deletions(-)
>
> diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
> index 00452cb..4453d1d 100644
> --- a/fs/xfs/xfs_aops.c
> +++ b/fs/xfs/xfs_aops.c
...
> @@ -1163,29 +1147,36 @@ xfs_vm_writepage(
> if (end_index > last_index)
> end_index = last_index;
>
> - xfs_cluster_write(inode, page->index + 1, &imap, &ioend,
> - wbc, end_index);
> + xfs_cluster_write(inode, page->index + 1, wpc, wbc, end_index);
> }
>
> -
> - /*
> - * Reserve log space if we might write beyond the on-disk inode size.
> - */
> - err = 0;
> - if (ioend->io_type != XFS_IO_UNWRITTEN && xfs_ioend_is_append(ioend))
> - err = xfs_setfilesize_trans_alloc(ioend);
> -
> - xfs_submit_ioend(wbc, iohead, err);
> -
> return 0;
>
> error:
> - if (iohead)
> - xfs_cancel_ioend(iohead);
> + /*
> + * We have to fail the iohead here because we buffers locked in the
> + * ioend chain. If we don't do this, we'll deadlock invalidating the
> + * page as that tries to lock the buffers on the page. Also, because we
> + * have set pages under writeback, we have to run IO completion to mark
> + * the error state of the IO appropriately, so we can't cancel the ioend
> + * directly here. That means we have to mark this page as under
> + * writeback if we included any buffers from it in the ioend chain.
> + */
> + if (count)
> + xfs_start_page_writeback(page, 0, count);
> + xfs_writepage_submit(wpc, wbc, err);
We make the xfs_writepage_submit() error case call here because...
>
> - xfs_aops_discard_page(page);
> - ClearPageUptodate(page);
> - unlock_page(page);
> + /*
> + * We can only discard the page we had the IO error on if we haven't
> + * included it in the ioend above. If it has already been errored out,
> + * the it is unlocked and we can't touch it here.
> + */
> + if (!count) {
> + xfs_aops_discard_page(page);
> + ClearPageUptodate(page);
> + unlock_page(page);
> + }
> + mapping_set_error(page->mapping, err);
> return err;
>
> redirty:
> @@ -1195,12 +1186,36 @@ redirty:
> }
>
> STATIC int
> +xfs_vm_writepage(
> + struct page *page,
> + struct writeback_control *wbc)
> +{
> + struct xfs_writepage_ctx wpc = {
> + .io_type = XFS_IO_OVERWRITE,
> + };
> + int ret;
> +
> + ret = xfs_do_writepage(page, wbc, &wpc);
> + if (ret)
> + return ret;
> + return xfs_writepage_submit(&wpc, wbc, ret);
... the callers only call it when ret == 0. Can we eliminate the error
call down in xfs_do_writepage() and just invoke this consistently from
the writepage(s) callers?
Brian
> +}
> +
> +STATIC int
> xfs_vm_writepages(
> struct address_space *mapping,
> struct writeback_control *wbc)
> {
> + struct xfs_writepage_ctx wpc = {
> + .io_type = XFS_IO_OVERWRITE,
> + };
> + int ret;
> +
> xfs_iflags_clear(XFS_I(mapping->host), XFS_ITRUNCATED);
> - return generic_writepages(mapping, wbc);
> + ret = write_cache_pages(mapping, wbc, xfs_do_writepage, &wpc);
> + if (ret)
> + return ret;
> + return xfs_writepage_submit(&wpc, wbc, ret);
> }
>
> /*
> --
> 2.5.0
>
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