[PATCH 03/10] readahead: Properly shorten readahead when falling back to do_page_cache_ra()

[Jan Kara <jack@suse.cz>]

When we succeed in creating some folios in page_cache_ra_order() but
then need to fallback to single page folios, we don't shorten the amount
to read passed to do_page_cache_ra() by the amount we've already read.
This then results in reading more and also in placing another readahead
mark in the middle of the readahead window which confuses readahead
code. Fix the problem by properly reducing number of pages to read.

Signed-off-by: Jan Kara <jack@suse.cz>
---
 mm/readahead.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/mm/readahead.c b/mm/readahead.c
index af0fbd302a38..1c58e0463be1 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -491,7 +491,8 @@ void page_cache_ra_order(struct readahead_control *ractl,
 		struct file_ra_state *ra, unsigned int new_order)
 {
 	struct address_space *mapping = ractl->mapping;
-	pgoff_t index = readahead_index(ractl);
+	pgoff_t start = readahead_index(ractl);
+	pgoff_t index = start;
 	pgoff_t limit = (i_size_read(mapping->host) - 1) >> PAGE_SHIFT;
 	pgoff_t mark = index + ra->size - ra->async_size;
 	unsigned int nofs;
@@ -544,7 +545,7 @@ void page_cache_ra_order(struct readahead_control *ractl,
 	if (!err)
 		return;
 fallback:
-	do_page_cache_ra(ractl, ra->size, ra->async_size);
+	do_page_cache_ra(ractl, ra->size - (index - start), ra->async_size);
 }
 
 /*
-- 
2.35.3