[obsolete] readahead-correct-the-start-and-size-in-ondemand_readahead.patch removed from -mm tree

[obsolete] readahead-correct-the-start-and-size-in-ondemand_readahead.patch removed from -mm tree

[Andrew Morton]

The quilt patch titled
     Subject: readahead: correct the start and size in ondemand_readahead()
has been removed from the -mm tree.  Its filename was
     readahead-correct-the-start-and-size-in-ondemand_readahead.patch

This patch was dropped because it is obsolete

------------------------------------------------------
From: Yin Fengwei <fengwei.yin@intel.com>
Subject: readahead: correct the start and size in ondemand_readahead()
Date: Wed, 28 Jun 2023 12:43:03 +0800

Commit 9425c591e06a ("page cache: fix page_cache_next/prev_miss off by
one") updated the page_cache_next_miss() to return the index beyond range.

But it breaks the start/size of ra in ondemand_readahead() because the
offset by one is accumulated to readahead_index.  As a consequence, not
best readahead order is picked.

Tracing of the order parameter of filemap_alloc_folio() showed:
     page order    : count     distribution
        0          : 892073   |                                        |
        1          : 0        |                                        |
        2          : 65120457 |****************************************|
        3          : 32914005 |********************                    |
        4          : 33020991 |********************                    |
with 9425c591e06a9.

With parent commit:
     page order    : count     distribution
        0          : 3417288  |****                                    |
        1          : 0        |                                        |
        2          : 877012   |*                                       |
        3          : 288      |                                        |
        4          : 5607522  |*******                                 |
        5          : 29974228 |****************************************|

Fix the issue by removing the offset by one when page_cache_next_miss()
returns no gaps in the range.

After the fix:
    page order     : count     distribution
        0          : 2598561  |***                                     |
        1          : 0        |                                        |
        2          : 687739   |                                        |
        3          : 288      |                                        |
        4          : 207210   |                                        |
        5          : 32628260 |****************************************|

Link: https://lkml.kernel.org/r/20230628044303.1412624-1-fengwei.yin@intel.com
Fixes: 9425c591e06a ("page cache: fix page_cache_next/prev_miss off by one")
Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202306211346.1e9ff03e-oliver.sang@intel.com
Signed-off-by: Yin Fengwei <fengwei.yin@intel.com>
Cc: Ackerley Tng <ackerleytng@google.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/readahead.c |   10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

--- a/mm/readahead.c~readahead-correct-the-start-and-size-in-ondemand_readahead
+++ a/mm/readahead.c
@@ -613,9 +613,17 @@ static void ondemand_readahead(struct re
 				max_pages);
 		rcu_read_unlock();
 
-		if (!start || start - index > max_pages)
+		if (!start || start - index - 1 > max_pages)
 			return;
 
+		/*
+		 * If no gaps in the range, page_cache_next_miss() returns
+		 * index beyond range. Adjust it back to make sure
+		 * ractl->_index is updated correctly later.
+		 */
+		if ((start - index - 1) == max_pages)
+			start--;
+
 		ra->start = start;
 		ra->size = start - index;	/* old async_size */
 		ra->size += req_size;
_

Patches currently in -mm which might be from fengwei.yin@intel.com are