[PATCH] readahead: Align window end in pagecache_ra_order()

[Jan Kara]

---
 mm/readahead.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/mm/readahead.c b/mm/readahead.c
index 6e5563290287..62e204eb3e7c 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -490,7 +490,7 @@ void page_cache_ra_order(struct readahead_control *ractl,
 	unsigned int nofs;
 	int err = 0;
 	gfp_t gfp = readahead_gfp_mask(mapping);
-	unsigned int new_order = ra->order;
+	unsigned int new_order = ra->order, last_order = 0;
 
 	trace_page_cache_ra_order(mapping->host, start, ra);
 	if (!mapping_large_folio_support(mapping)) {
@@ -532,10 +532,22 @@ void page_cache_ra_order(struct readahead_control *ractl,
 		/* Don't allocate pages past EOF */
 		while (order > min_order && index + (1UL << order) - 1 > limit)
 			order--;
+		/*
+		 * If we are allowed to align the end of readahead window, stop
+		 * the readahead as soon as we have to reduce folio order due
+		 * to it exceeding the RA window.
+		 */
+		if (ractl->_align_end && order < last_order) {
+			ra->size = index - start;
+			if (ra->async_size > ra->size)
+				ra->async_size = ra->size;
+			break;
+		}
 		err = ra_alloc_folio(ractl, index, mark, order, gfp);
 		if (err)
 			break;
 		index += 1UL << order;
+		last_order = order;
 	}
 
 	read_pages(ractl);
-- 
2.53.0


--lgcir5uumdsu3tbv--