linux-kernel - [PATCH] Revert "page cache: fix page_cache_next/prev

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Date:   Tue, 25 Jul 2023 11:31:29 -0700
From:   Sidhartha Kumar <sidhartha.kumar@...cle.com>
To:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org
Cc:     Mike Kravetz <mike.kravetz@...cle.com>,
        kernel test robot <oliver.sang@...el.com>,
        Sidhartha Kumar <sidhartha.kumar@...cle.com>,
        stable@...r.kernel.org, Thomas Backlund <tmb@....nu>,
        Ackerley Tng <ackerleytng@...gle.com>,
        Erdem Aktas <erdemaktas@...gle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Matthew Wilcox <willy@...radead.org>,
        Muchun Song <songmuchun@...edance.com>,
        Vishal Annapurve <vannapurve@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH] Revert "page cache: fix page_cache_next/prev_miss off by one"

From: Mike Kravetz <mike.kravetz@...cle.com>

commit 16f8eb3eea9eb2a1568279d64ca4dc977e7aa538 upstream

This reverts commit 9425c591e06a9ab27a145ba655fb50532cf0bcc9

The reverted commit fixed up routines primarily used by readahead code
such that they could also be used by hugetlb.  Unfortunately, this
caused a performance regression as pointed out by the Closes: tag.

The hugetlb code which uses page_cache_next_miss will be addressed in
a subsequent patch.

Link: https://lkml.kernel.org/r/20230621212403.174710-1-mike.kravetz@oracle.com
Fixes: 9425c591e06a ("page cache: fix page_cache_next/prev_miss off by one")
Signed-off-by: Mike Kravetz <mike.kravetz@...cle.com>
Reported-by: kernel test robot <oliver.sang@...el.com>
Closes: https://lore.kernel.org/oe-lkp/202306211346.1e9ff03e-oliver.sang@intel.com
Reviewed-by: Sidhartha Kumar <sidhartha.kumar@...cle.com>
Cc: stable@...r.kernel.org
Cc: Thomas Backlund <tmb@....nu>
Cc: Ackerley Tng <ackerleytng@...gle.com>
Cc: Erdem Aktas <erdemaktas@...gle.com>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Matthew Wilcox <willy@...radead.org>
Cc: Muchun Song <songmuchun@...edance.com>
Cc: Vishal Annapurve <vannapurve@...gle.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
---

As pointed out in [1], this patch was missed in the 6.4 stable tree.
Resending this patch with a Cc: stable.

[1]: https://lore.kernel.org/all/20230621212403.174710-1-mike.kravetz@oracle.com/T/#m9e33a9ccb76e4db123279b371cff57d4e1a1ed3a

 mm/filemap.c | 26 ++++++++++----------------
 1 file changed, 10 insertions(+), 16 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index 8abce63b259c9..a2006936a6ae2 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1760,9 +1760,7 @@ bool __folio_lock_or_retry(struct folio *folio, struct mm_struct *mm,
  *
  * Return: The index of the gap if found, otherwise an index outside the
  * range specified (in which case 'return - index >= max_scan' will be true).
- * In the rare case of index wrap-around, 0 will be returned.  0 will also
- * be returned if index == 0 and there is a gap at the index.  We can not
- * wrap-around if passed index == 0.
+ * In the rare case of index wrap-around, 0 will be returned.
  */
 pgoff_t page_cache_next_miss(struct address_space *mapping,
 			     pgoff_t index, unsigned long max_scan)
@@ -1772,13 +1770,12 @@ pgoff_t page_cache_next_miss(struct address_space *mapping,
 	while (max_scan--) {
 		void *entry = xas_next(&xas);
 		if (!entry || xa_is_value(entry))
-			return xas.xa_index;
-		if (xas.xa_index == 0 && index != 0)
-			return xas.xa_index;
+			break;
+		if (xas.xa_index == 0)
+			break;
 	}
 
-	/* No gaps in range and no wrap-around, return index beyond range */
-	return xas.xa_index + 1;
+	return xas.xa_index;
 }
 EXPORT_SYMBOL(page_cache_next_miss);
 
@@ -1799,9 +1796,7 @@ EXPORT_SYMBOL(page_cache_next_miss);
  *
  * Return: The index of the gap if found, otherwise an index outside the
  * range specified (in which case 'index - return >= max_scan' will be true).
- * In the rare case of wrap-around, ULONG_MAX will be returned.  ULONG_MAX
- * will also be returned if index == ULONG_MAX and there is a gap at the
- * index.  We can not wrap-around if passed index == ULONG_MAX.
+ * In the rare case of wrap-around, ULONG_MAX will be returned.
  */
 pgoff_t page_cache_prev_miss(struct address_space *mapping,
 			     pgoff_t index, unsigned long max_scan)
@@ -1811,13 +1806,12 @@ pgoff_t page_cache_prev_miss(struct address_space *mapping,
 	while (max_scan--) {
 		void *entry = xas_prev(&xas);
 		if (!entry || xa_is_value(entry))
-			return xas.xa_index;
-		if (xas.xa_index == ULONG_MAX && index != ULONG_MAX)
-			return xas.xa_index;
+			break;
+		if (xas.xa_index == ULONG_MAX)
+			break;
 	}
 
-	/* No gaps in range and no wrap-around, return index beyond range */
-	return xas.xa_index - 1;
+	return xas.xa_index;
 }
 EXPORT_SYMBOL(page_cache_prev_miss);
 
-- 
2.41.0