On Thu 14-12-23 14:25:37, Christoph Hellwig wrote:
> From: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>
>
> Collapse the two nested loops into one. This is needed as a step
> towards turning this into an iterator.
>
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
It would be good to mention in the changelog that we drop the condition
index <= end and just rely on filemap_get_folios_tag() to return 0 entries
when index > end. This actually has a subtle implication when end == -1
because then the returned index will be -1 as well and thus if there is
page present on index -1, we could be looping indefinitely. But I think
that's mostly a theoretical concern so I'd be fine with just mentioning
this subtlety in the changelog and possibly in a comment in the code.
Honza
> ---
> mm/page-writeback.c | 98 ++++++++++++++++++++++-----------------------
> 1 file changed, 49 insertions(+), 49 deletions(-)
>
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index 5a3df8665ff4f9..2087d16115710e 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -2460,6 +2460,7 @@ int write_cache_pages(struct address_space *mapping,
> void *data)
> {
> int error;
> + int i = 0;
>
> if (wbc->range_cyclic) {
> wbc->index = mapping->writeback_index; /* prev offset */
> @@ -2477,67 +2478,66 @@ int write_cache_pages(struct address_space *mapping,
> folio_batch_init(&wbc->fbatch);
> wbc->err = 0;
>
> - while (wbc->index <= wbc->end) {
> - int i;
> -
> - writeback_get_batch(mapping, wbc);
> + for (;;) {
> + struct folio *folio;
> + unsigned long nr;
>
> + if (i == wbc->fbatch.nr) {
> + writeback_get_batch(mapping, wbc);
> + i = 0;
> + }
> if (wbc->fbatch.nr == 0)
> break;
>
> - for (i = 0; i < wbc->fbatch.nr; i++) {
> - struct folio *folio = wbc->fbatch.folios[i];
> - unsigned long nr;
> + folio = wbc->fbatch.folios[i++];
>
> - wbc->done_index = folio->index;
> + wbc->done_index = folio->index;
>
> - folio_lock(folio);
> - if (!should_writeback_folio(mapping, wbc, folio)) {
> - folio_unlock(folio);
> - continue;
> - }
> + folio_lock(folio);
> + if (!should_writeback_folio(mapping, wbc, folio)) {
> + folio_unlock(folio);
> + continue;
> + }
>
> - trace_wbc_writepage(wbc, inode_to_bdi(mapping->host));
> -
> - error = writepage(folio, wbc, data);
> - nr = folio_nr_pages(folio);
> - if (unlikely(error)) {
> - /*
> - * Handle errors according to the type of
> - * writeback. There's no need to continue for
> - * background writeback. Just push done_index
> - * past this page so media errors won't choke
> - * writeout for the entire file. For integrity
> - * writeback, we must process the entire dirty
> - * set regardless of errors because the fs may
> - * still have state to clear for each page. In
> - * that case we continue processing and return
> - * the first error.
> - */
> - if (error == AOP_WRITEPAGE_ACTIVATE) {
> - folio_unlock(folio);
> - error = 0;
> - } else if (wbc->sync_mode != WB_SYNC_ALL) {
> - wbc->err = error;
> - wbc->done_index = folio->index + nr;
> - return writeback_finish(mapping,
> - wbc, true);
> - }
> - if (!wbc->err)
> - wbc->err = error;
> - }
> + trace_wbc_writepage(wbc, inode_to_bdi(mapping->host));
>
> + error = writepage(folio, wbc, data);
> + nr = folio_nr_pages(folio);
> + if (unlikely(error)) {
> /*
> - * We stop writing back only if we are not doing
> - * integrity sync. In case of integrity sync we have to
> - * keep going until we have written all the pages
> - * we tagged for writeback prior to entering this loop.
> + * Handle errors according to the type of
> + * writeback. There's no need to continue for
> + * background writeback. Just push done_index
> + * past this page so media errors won't choke
> + * writeout for the entire file. For integrity
> + * writeback, we must process the entire dirty
> + * set regardless of errors because the fs may
> + * still have state to clear for each page. In
> + * that case we continue processing and return
> + * the first error.
> */
> - wbc->nr_to_write -= nr;
> - if (wbc->nr_to_write <= 0 &&
> - wbc->sync_mode == WB_SYNC_NONE)
> + if (error == AOP_WRITEPAGE_ACTIVATE) {
> + folio_unlock(folio);
> + error = 0;
> + } else if (wbc->sync_mode != WB_SYNC_ALL) {
> + wbc->err = error;
> + wbc->done_index = folio->index + nr;
> return writeback_finish(mapping, wbc, true);
> + }
> + if (!wbc->err)
> + wbc->err = error;
> }
> +
> + /*
> + * We stop writing back only if we are not doing
> + * integrity sync. In case of integrity sync we have to
> + * keep going until we have written all the pages
> + * we tagged for writeback prior to entering this loop.
> + */
> + wbc->nr_to_write -= nr;
> + if (wbc->nr_to_write <= 0 &&
> + wbc->sync_mode == WB_SYNC_NONE)
> + return writeback_finish(mapping, wbc, true);
> }
>
> return writeback_finish(mapping, wbc, false);
> --
> 2.39.2
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
