From a5718a922fc374ebf24c45d4d3fd11f84ad064d6 Mon Sep 17 00:00:00 2001
From: Jens Axboe <axboe@kernel.dk>
Date: Fri, 5 Nov 2021 13:37:13 -0700
Subject: [PATCH] mm: move more expensive part of XA setup out of mapping check

References: bsc#1190208 (MM functional and performance backports)
Patch-mainline: v5.16-rc1
Git-commit: f8ee8909ac818e555ef18b57b0ee4b9fd0478b82

The fast path here is not needing any writeback, yet we spend time
setting up the xarray lookup data upfront.  Move the part that actually
needs to iterate the address space mapping into a separate helper,
saving ~30% of the time here.

Link: https://lkml.kernel.org/r/49f67983-b802-8929-edab-d807f745c9ca@kernel.dk
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Mel Gorman <mgorman@suse.de>
---
 mm/filemap.c | 43 +++++++++++++++++++++++++------------------
 1 file changed, 25 insertions(+), 18 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index e3aa29fd32d3..2463bf255688 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -621,6 +621,30 @@ static bool mapping_needs_writeback(struct address_space *mapping)
 	return mapping->nrpages;
 }
 
+static bool filemap_range_has_writeback(struct address_space *mapping,
+					loff_t start_byte, loff_t end_byte)
+{
+	XA_STATE(xas, &mapping->i_pages, start_byte >> PAGE_SHIFT);
+	pgoff_t max = end_byte >> PAGE_SHIFT;
+	struct page *page;
+
+	if (end_byte < start_byte)
+		return false;
+
+	rcu_read_lock();
+	xas_for_each(&xas, page, max) {
+		if (xas_retry(&xas, page))
+			continue;
+		if (xa_is_value(page))
+			continue;
+		if (PageDirty(page) || PageLocked(page) || PageWriteback(page))
+			break;
+	}
+	rcu_read_unlock();
+	return page != NULL;
+
+}
+
 /**
  * filemap_range_needs_writeback - check if range potentially needs writeback
  * @mapping:           address space within which to check
@@ -638,29 +662,12 @@ static bool mapping_needs_writeback(struct address_space *mapping)
 bool filemap_range_needs_writeback(struct address_space *mapping,
 				   loff_t start_byte, loff_t end_byte)
 {
-	XA_STATE(xas, &mapping->i_pages, start_byte >> PAGE_SHIFT);
-	pgoff_t max = end_byte >> PAGE_SHIFT;
-	struct page *page;
-
 	if (!mapping_needs_writeback(mapping))
 		return false;
 	if (!mapping_tagged(mapping, PAGECACHE_TAG_DIRTY) &&
 	    !mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK))
 		return false;
-	if (end_byte < start_byte)
-		return false;
-
-	rcu_read_lock();
-	xas_for_each(&xas, page, max) {
-		if (xas_retry(&xas, page))
-			continue;
-		if (xa_is_value(page))
-			continue;
-		if (PageDirty(page) || PageLocked(page) || PageWriteback(page))
-			break;
-	}
-	rcu_read_unlock();
-	return page != NULL;
+	return filemap_range_has_writeback(mapping, start_byte, end_byte);
 }
 EXPORT_SYMBOL_GPL(filemap_range_needs_writeback);