[PATCH 06/19] writeback: Factor out writeback_finish()

Christoph Hellwig
2024-01-25T08:58:32Z

From: "Matthew Wilcox (Oracle)" <willy@infradead.org>

Instead of having a 'done' variable that controls the nested loops,
have a writeback_finish() that can be returned directly. This involves
keeping more things in writeback_control, but it's just moving stuff
allocated on the stack to being allocated slightly earlier on the stack.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
[hch: heavily rebased, reordered and commented struct writeback_control]
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jan Kara <jack@suse.cz>
Acked-by: Dave Chinner <dchinner@redhat.com>
---
include/linux/writeback.h | 6 +++
mm/page-writeback.c | 79 ++++++++++++++++++++-------------------
2 files changed, 47 insertions(+), 38 deletions(-)

diff --git a/include/linux/writeback.h b/include/linux/writeback.h
index 4b8cf9e4810bad..7d60a68fa4ea47 100644
--- a/include/linux/writeback.h
+++ b/include/linux/writeback.h
@@ -11,6 +11,7 @@
#include <linux/flex_proportions.h>
#include <linux/backing-dev-defs.h>
#include <linux/blk_types.h>
+#include <linux/pagevec.h>

struct bio;

@@ -40,6 +41,7 @@ enum writeback_sync_modes {
* in a manner such that unspecified fields are set to zero.
*/
struct writeback_control {
+ /* public fields that can be set and/or consumed by the caller: */
long nr_to_write; /* Write this many pages, and decrement
this for each page written */
long pages_skipped; /* Pages which were not written */
@@ -77,6 +79,10 @@ struct writeback_control {
*/
struct swap_iocb **swap_plug;

+ /* internal fields used by the ->writepages implementation: */
+ struct folio_batch fbatch;
+ int err;
+
#ifdef CONFIG_CGROUP_WRITEBACK
struct bdi_writeback *wb; /* wb this writeback is issued under */
struct inode *inode; /* inode being written out */
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 437745a511c634..fcd90a176d806c 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2360,6 +2360,29 @@ void tag_pages_for_writeback(struct address_space *mapping,
}
EXPORT_SYMBOL(tag_pages_for_writeback);

+static void writeback_finish(struct address_space *mapping,
+ struct writeback_control *wbc, pgoff_t done_index)
+{
+ folio_batch_release(&wbc->fbatch);
+
+ /*
+ * For range cyclic writeback we need to remember where we stopped so
+ * that we can continue there next time we are called. If we hit the
+ * last page and there is more work to be done, wrap back to the start
+ * of the file.
+ *
+ * For non-cyclic writeback we always start looking up at the beginning
+ * of the file if we are called again, which can only happen due to
+ * -ENOMEM from the file system.
+ */
+ if (wbc->range_cyclic) {
+ if (wbc->err || wbc->nr_to_write <= 0)
+ mapping->writeback_index = done_index;
+ else
+ mapping->writeback_index = 0;
+ }
+}
+
/**
* write_cache_pages - walk the list of dirty pages of the given address space and write all of them.
* @mapping: address space structure to write
@@ -2395,17 +2418,12 @@ int write_cache_pages(struct address_space *mapping,
struct writeback_control *wbc, writepage_t writepage,
void *data)
{
- int ret = 0;
- int done = 0;
int error;
- struct folio_batch fbatch;
int nr_folios;
pgoff_t index;
pgoff_t end; /* Inclusive */
- pgoff_t done_index;
xa_mark_t tag;

- folio_batch_init(&fbatch);
if (wbc->range_cyclic) {
index = mapping->writeback_index; /* prev offset */
end = -1;
@@ -2419,22 +2437,23 @@ int write_cache_pages(struct address_space *mapping,
} else {
tag = PAGECACHE_TAG_DIRTY;
}
- done_index = index;
- while (!done && (index <= end)) {
+
+ folio_batch_init(&wbc->fbatch);
+ wbc->err = 0;
+
+ while (index <= end) {
int i;

nr_folios = filemap_get_folios_tag(mapping, &index, end,
- tag, &fbatch);
+ tag, &wbc->fbatch);

if (nr_folios == 0)
break;

for (i = 0; i < nr_folios; i++) {
- struct folio *folio = fbatch.folios[i];
+ struct folio *folio = wbc->fbatch.folios[i];
unsigned long nr;

- done_index = folio->index;
-
folio_lock(folio);

/*
@@ -2481,6 +2500,9 @@ int write_cache_pages(struct address_space *mapping,
folio_unlock(folio);
error = 0;
}
+
+ if (error && !wbc->err)
+ wbc->err = error;

/*
* For integrity sync we have to keep going until we
@@ -2496,38 +2518,19 @@ int write_cache_pages(struct address_space *mapping,
* off and media errors won't choke writeout for the
* entire file.
*/
- if (error && !ret)
- ret = error;
- if (wbc->sync_mode == WB_SYNC_NONE) {
- if (ret || wbc->nr_to_write <= 0) {
- done_index = folio->index + nr;
- done = 1;
- break;
- }
+ if (wbc->sync_mode == WB_SYNC_NONE &&
+ (wbc->err || wbc->nr_to_write <= 0)) {
+ writeback_finish(mapping, wbc,
+ folio->index + nr);
+ return error;
}
}
- folio_batch_release(&fbatch);
+ folio_batch_release(&wbc->fbatch);
cond_resched();
}

- /*
- * For range cyclic writeback we need to remember where we stopped so
- * that we can continue there next time we are called. If we hit the
- * last page and there is more work to be done, wrap back to the start
- * of the file.
- *
- * For non-cyclic writeback we always start looking up at the beginning
- * 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;
- }
-
- return ret;
+ writeback_finish(mapping, wbc, 0);
+ return 0;
}
EXPORT_SYMBOL(write_cache_pages);

--
2.39.2