+ revert-page-cache-fix-page_cache_next-prev_miss-off-by-one.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: Revert "page cache: fix page_cache_next/prev_miss off by one"
has been added to the -mm mm-unstable branch.  Its filename is
     revert-page-cache-fix-page_cache_next-prev_miss-off-by-one.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/revert-page-cache-fix-page_cache_next-prev_miss-off-by-one.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Mike Kravetz <mike.kravetz@oracle.com>
Subject: Revert "page cache: fix page_cache_next/prev_miss off by one"
Date: Wed, 21 Jun 2023 14:24:02 -0700

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@oracle.com>
Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202306211346.1e9ff03e-oliver.sang@intel.com
Cc: Ackerley Tng <ackerleytng@google.com>
Cc: Erdem Aktas <erdemaktas@google.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Muchun Song <songmuchun@bytedance.com>
Cc: Reviewed-by Sidhartha Kumar <sidhartha.kumar@oracle.com>
Cc: Vishal Annapurve <vannapurve@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

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

--- a/mm/filemap.c~revert-page-cache-fix-page_cache_next-prev_miss-off-by-one
+++ a/mm/filemap.c
@@ -1728,9 +1728,7 @@ bool __folio_lock_or_retry(struct folio
  *
  * 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)
@@ -1740,13 +1738,12 @@ pgoff_t page_cache_next_miss(struct addr
 	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);
 
@@ -1767,9 +1764,7 @@ 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)
@@ -1779,13 +1774,12 @@ pgoff_t page_cache_prev_miss(struct addr
 	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);
 
_

Patches currently in -mm which might be from mike.kravetz@oracle.com are

revert-page-cache-fix-page_cache_next-prev_miss-off-by-one.patch
hugetlb-revert-use-of-page_cache_next_miss.patch