[PATCH 04/19] writeback: only update ->writeback_index for range_cyclic writeback

Christoph Hellwig
2024-01-25T08:58:28Z

mapping->writeback_index is only [1] used as the starting point for
range_cyclic writeback, so there is no point in updating it for other
types of writeback.

[1] except for btrfs_defrag_file which does really odd things with
mapping->writeback_index. But btrfs doesn't use write_cache_pages at
all, so this isn't relevant here.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jan Kara <jack@suse.cz>
Acked-by: Dave Chinner <dchinner@redhat.com>
---
mm/page-writeback.c | 24 ++++++++++++++----------
1 file changed, 14 insertions(+), 10 deletions(-)

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 259c37bc34d2a7..437745a511c634 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2403,7 +2403,6 @@ int write_cache_pages(struct address_space *mapping,
pgoff_t index;
pgoff_t end; /* Inclusive */
pgoff_t done_index;
- int range_whole = 0;
xa_mark_t tag;

folio_batch_init(&fbatch);
@@ -2413,8 +2412,6 @@ int write_cache_pages(struct address_space *mapping,
} else {
index = wbc->range_start >> PAGE_SHIFT;
end = wbc->range_end >> PAGE_SHIFT;
- if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
- range_whole = 1;
}
if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages) {
tag_pages_for_writeback(mapping, index, end);
@@ -2514,14 +2511,21 @@ int write_cache_pages(struct address_space *mapping,
}

/*
- * If we hit the last page and there is more work to be done: wrap
- * back the index back to the start of the file for the next
- * time we are called.
+ * 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 && !done)
- done_index = 0;
- if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
- mapping->writeback_index = done_index;
+ if (wbc->range_cyclic) {
+ if (done)
+ mapping->writeback_index = done_index;
+ else
+ mapping->writeback_index = 0;
+ }

return ret;
}
--
2.39.2