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From: Christoph Hellwig <hch@lst.de>
To: linux-mm@kvack.org
Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>,
	Jan Kara <jack@suse.com>,
	David Howells <dhowells@redhat.com>,
	Brian Foster <bfoster@redhat.com>,
	linux-fsdevel@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: [PATCH 08/17] writeback: Factor should_writeback_folio() out of write_cache_pages()
Date: Mon, 18 Dec 2023 16:35:44 +0100
Message-Id: <20231218153553.807799-9-hch@lst.de>
In-Reply-To: <20231218153553.807799-1-hch@lst.de>
References: <20231218153553.807799-1-hch@lst.de>
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From: "Matthew Wilcox (Oracle)" <willy@infradead.org>

Reduce write_cache_pages() by about 30 lines; much of it is commentary,
but it all bundles nicely into an obvious function.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 mm/page-writeback.c | 59 ++++++++++++++++++++++++---------------------
 1 file changed, 32 insertions(+), 27 deletions(-)

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 798e5264dc0353..2a004c0b9bdfbf 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2406,6 +2406,36 @@ static void writeback_get_batch(struct address_space *mapping,
 			wbc_to_tag(wbc), &wbc->fbatch);
 }
 
+static bool should_writeback_folio(struct address_space *mapping,
+		struct writeback_control *wbc, struct folio *folio)
+{
+	/*
+	 * Folio truncated or invalidated. We can freely skip it then,
+	 * even for data integrity operations: the folio has disappeared
+	 * concurrently, so there could be no real expectation of this
+	 * data integrity operation even if there is now a new, dirty
+	 * folio at the same pagecache index.
+	 */
+	if (unlikely(folio->mapping != mapping))
+		return false;
+
+	/* Did somebody write it for us? */
+	if (!folio_test_dirty(folio))
+		return false;
+
+	if (folio_test_writeback(folio)) {
+		if (wbc->sync_mode == WB_SYNC_NONE)
+			return false;
+		folio_wait_writeback(folio);
+	}
+
+	BUG_ON(folio_test_writeback(folio));
+	if (!folio_clear_dirty_for_io(folio))
+		return false;
+
+	return true;
+}
+
 /**
  * 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
@@ -2470,38 +2500,13 @@ int write_cache_pages(struct address_space *mapping,
 			unsigned long nr;
 
 			folio_lock(folio);
-
-			/*
-			 * Page truncated or invalidated. We can freely skip it
-			 * then, even for data integrity operations: the page
-			 * has disappeared concurrently, so there could be no
-			 * real expectation of this data integrity operation
-			 * even if there is now a new, dirty page at the same
-			 * pagecache address.
-			 */
-			if (unlikely(folio->mapping != mapping)) {
-continue_unlock:
+			if (!should_writeback_folio(mapping, wbc, folio)) {
 				folio_unlock(folio);
 				continue;
 			}
 
-			if (!folio_test_dirty(folio)) {
-				/* someone wrote it for us */
-				goto continue_unlock;
-			}
-
-			if (folio_test_writeback(folio)) {
-				if (wbc->sync_mode != WB_SYNC_NONE)
-					folio_wait_writeback(folio);
-				else
-					goto continue_unlock;
-			}
-
-			BUG_ON(folio_test_writeback(folio));
-			if (!folio_clear_dirty_for_io(folio))
-				goto continue_unlock;
-
 			trace_wbc_writepage(wbc, inode_to_bdi(mapping->host));
+
 			error = writepage(folio, wbc, data);
 			nr = folio_nr_pages(folio);
 			wbc->nr_to_write -= nr;
-- 
2.39.2