linux-kernel - [PATCH v8 33/63] page cache: Convert filemap_range_has

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Message-Id: <20180306192413.5499-34-willy@infradead.org>
Date:   Tue,  6 Mar 2018 11:23:43 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Matthew Wilcox <mawilcox@...rosoft.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org,
        Ryusuke Konishi <konishi.ryusuke@....ntt.co.jp>,
        linux-nilfs@...r.kernel.org, linux-btrfs@...r.kernel.org
Subject: [PATCH v8 33/63] page cache: Convert filemap_range_has_page to XArray

From: Matthew Wilcox <mawilcox@...rosoft.com>

Instead of calling find_get_pages_range() and putting any reference,
use xas_find() to iterate over any entries in the range, skipping the
shadow/swap entries.

Signed-off-by: Matthew Wilcox <mawilcox@...rosoft.com>
---
 mm/filemap.c | 26 ++++++++++++++++++--------
 1 file changed, 18 insertions(+), 8 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index 86c83014c909..9bc417913269 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -458,20 +458,30 @@ EXPORT_SYMBOL(filemap_flush);
 bool filemap_range_has_page(struct address_space *mapping,
 			   loff_t start_byte, loff_t end_byte)
 {
-	pgoff_t index = start_byte >> PAGE_SHIFT;
-	pgoff_t end = end_byte >> PAGE_SHIFT;
 	struct page *page;
+	XA_STATE(xas, &mapping->i_pages, start_byte >> PAGE_SHIFT);
+	pgoff_t max = end_byte >> PAGE_SHIFT;
 
 	if (end_byte < start_byte)
 		return false;
 
-	if (mapping->nrpages == 0)
-		return false;
+	rcu_read_lock();
+	do {
+		page = xas_find(&xas, max);
+		if (xas_retry(&xas, page))
+			continue;
+		/* Shadow entries don't count */
+		if (xa_is_value(page))
+			continue;
+		/*
+		 * We don't need to try to pin this page; we're about to
+		 * release the RCU lock anyway.  It is enough to know that
+		 * there was a page here recently.
+		 */
+	} while (0);
+	rcu_read_unlock();
 
-	if (!find_get_pages_range(mapping, &index, end, 1, &page))
-		return false;
-	put_page(page);
-	return true;
+	return page != NULL;
 }
 EXPORT_SYMBOL(filemap_range_has_page);
 
-- 
2.16.1