The 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 set correct start/size of ra in ondemand_readahead().
Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
Closes: https://lore.kernel.org/oe-lkp/202306211346.1e9ff03e-oliver.sang@xxxxxxxxx
Fixes: 9425c591e06a ("page cache: fix page_cache_next/prev_miss off by one")
Signed-off-by: Yin Fengwei <fengwei.yin@xxxxxxxxx>
---
mm/readahead.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/mm/readahead.c b/mm/readahead.c
index 47afbca1d122e..a1b8c628851a9 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -614,11 +614,11 @@ 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;
- ra->start = start;
- ra->size = start - index; /* old async_size */
+ ra->start = start - 1;
+ ra->size = start - index - 1; /* old async_size */
ra->size += req_size;
ra->size = get_next_ra_size(ra, max_pages);
ra->async_size = ra->size;
--
2.39.2
