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Message-ID: <20240205113412.ceemxahic7bpodip@quack3>
Date: Mon, 5 Feb 2024 12:34:12 +0100
From: Jan Kara <jack@...e.cz>
To: Christoph Hellwig <hch@....de>
Cc: linux-mm@...ck.org, Matthew Wilcox <willy@...radead.org>,
Jan Kara <jack@...e.com>, David Howells <dhowells@...hat.com>,
Brian Foster <bfoster@...hat.com>,
Christian Brauner <brauner@...nel.org>,
"Darrick J. Wong" <djwong@...nel.org>, linux-xfs@...r.kernel.org,
linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 05/13] writeback: rework the loop termination condition
in write_cache_pages
On Sat 03-02-24 08:11:39, Christoph Hellwig wrote:
> Rework the way we deal with the cleanup after the writepage call.
>
> First handle the magic AOP_WRITEPAGE_ACTIVATE separately from real error
> returns to get it out of the way of the actual error handling path.
>
> The split the handling on intgrity vs non-integrity branches first,
> and return early using a goto for the non-ingegrity early loop condition
> to remove the need for the done and done_index local variables, and for
> assigning the error to ret when we can just return error directly.
>
> Signed-off-by: Christoph Hellwig <hch@....de>
Looks good. Feel free to add:
Reviewed-by: Jan Kara <jack@...e.cz>
Honza
> ---
> mm/page-writeback.c | 84 ++++++++++++++++++---------------------------
> 1 file changed, 33 insertions(+), 51 deletions(-)
>
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index c7c494526bc650..88b2c4c111c01b 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -2396,13 +2396,12 @@ int write_cache_pages(struct address_space *mapping,
> void *data)
> {
> int ret = 0;
> - int done = 0;
> int error;
> struct folio_batch fbatch;
> + struct folio *folio;
> int nr_folios;
> pgoff_t index;
> pgoff_t end; /* Inclusive */
> - pgoff_t done_index;
> xa_mark_t tag;
>
> folio_batch_init(&fbatch);
> @@ -2419,8 +2418,7 @@ int write_cache_pages(struct address_space *mapping,
> } else {
> tag = PAGECACHE_TAG_DIRTY;
> }
> - done_index = index;
> - while (!done && (index <= end)) {
> + while (index <= end) {
> int i;
>
> nr_folios = filemap_get_folios_tag(mapping, &index, end,
> @@ -2430,11 +2428,7 @@ int write_cache_pages(struct address_space *mapping,
> break;
>
> for (i = 0; i < nr_folios; i++) {
> - struct folio *folio = fbatch.folios[i];
> - unsigned long nr;
> -
> - done_index = folio->index;
> -
> + folio = fbatch.folios[i];
> folio_lock(folio);
>
> /*
> @@ -2469,45 +2463,32 @@ int write_cache_pages(struct address_space *mapping,
>
> trace_wbc_writepage(wbc, inode_to_bdi(mapping->host));
> error = writepage(folio, wbc, data);
> - nr = folio_nr_pages(folio);
> - wbc->nr_to_write -= nr;
> - 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) {
> - ret = error;
> - done_index = folio->index + nr;
> - done = 1;
> - break;
> - }
> - if (!ret)
> - ret = error;
> + wbc->nr_to_write -= folio_nr_pages(folio);
> +
> + if (error == AOP_WRITEPAGE_ACTIVATE) {
> + folio_unlock(folio);
> + error = 0;
> }
>
> /*
> - * 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.
> + * For integrity writeback we have to keep going until
> + * we have written all the folios we tagged for
> + * writeback above, even if we run past wbc->nr_to_write
> + * or encounter errors.
> + * We stash away the first error we encounter in
> + * wbc->saved_err so that it can be retrieved when we're
> + * done. This is because the file system may still have
> + * state to clear for each folio.
> + *
> + * For background writeback we exit as soon as we run
> + * past wbc->nr_to_write or encounter the first error.
> */
> - done_index = folio->index + nr;
> - if (wbc->nr_to_write <= 0 &&
> - wbc->sync_mode == WB_SYNC_NONE) {
> - done = 1;
> - break;
> + if (wbc->sync_mode == WB_SYNC_ALL) {
> + if (error && !ret)
> + ret = error;
> + } else {
> + if (error || wbc->nr_to_write <= 0)
> + goto done;
> }
> }
> folio_batch_release(&fbatch);
> @@ -2524,14 +2505,15 @@ int write_cache_pages(struct address_space *mapping,
> * of the file if we are called again, which can only happen due to
> * -ENOMEM from the file system.
> */
> - if (wbc->range_cyclic) {
> - if (done)
> - mapping->writeback_index = done_index;
> - else
> - mapping->writeback_index = 0;
> - }
> -
> + if (wbc->range_cyclic)
> + mapping->writeback_index = 0;
> return ret;
> +
> +done:
> + folio_batch_release(&fbatch);
> + if (wbc->range_cyclic)
> + mapping->writeback_index = folio->index + folio_nr_pages(folio);
> + return error;
> }
> EXPORT_SYMBOL(write_cache_pages);
>
> --
> 2.39.2
>
--
Jan Kara <jack@...e.com>
SUSE Labs, CR
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