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From: Yin Fengwei <fengwei.yin@intel.com>
Date: Wed, 28 Jun 2023 12:43:03 +0800
Subject: [PATCH 06/16] readahead: correct the start and size in
ondemand_readahead()
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.
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(-)
diff --git a/mm/readahead.c b/mm/readahead.c
index 6925e6959..1c1d26ad0 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -600,9 +600,17 @@ static void ondemand_readahead(struct readahead_control *ractl,
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;
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