Given we have a_ops->folio_order which passes the desired folio order, let's use
page_cache_sync_ra in fadvise(FADVISE_FAV_WILLNEED) to get large folios.

Before:
 f2fs_fadvise: dev = (252,16), ino = 14, i_size = 4294967296 offset:0, len:4294967296, advise:3
 page_cache_ra_unbounded: dev=252:16 ino=e index=0 nr_to_read=2048 lookahead_size=0
 page_cache_ra_unbounded: dev=252:16 ino=e index=2048 nr_to_read=2048 lookahead_size=0
 page_cache_ra_unbounded: dev=252:16 ino=e index=4096 nr_to_read=2048 lookahead_size=0
 page_cache_ra_unbounded: dev=252:16 ino=e index=6144 nr_to_read=2048 lookahead_size=0
 page_cache_ra_unbounded: dev=252:16 ino=e index=8192 nr_to_read=2048 lookahead_size=0
 page_cache_ra_unbounded: dev=252:16 ino=e index=10240 nr_to_read=2048 lookahead_size=0
 page_cache_ra_unbounded: dev=252:16 ino=e index=12288 nr_to_read=2048 lookahead_size=0
 page_cache_ra_unbounded: dev=252:16 ino=e index=14336 nr_to_read=2048 lookahead_size=0
 page_cache_ra_unbounded: dev=252:16 ino=e index=16384 nr_to_read=2048 lookahead_size=0
 page_cache_ra_unbounded: dev=252:16 ino=e index=18432 nr_to_read=2048 lookahead_size=0
 page_cache_ra_unbounded: dev=252:16 ino=e index=20480 nr_to_read=2048 lookahead_size=0
 page_cache_ra_unbounded: dev=252:16 ino=e index=22528 nr_to_read=2048 lookahead_size=0
 page_cache_ra_unbounded: dev=252:16 ino=e index=24576 nr_to_read=2048 lookahead_size=0
 ...
 page_cache_ra_unbounded: dev=252:16 ino=e index=1042432 nr_to_read=2048 lookahead_size=0

This is all zero-order page allocation.

After (order=0 by default):
 f2fs_fadvise: dev = (252,16), ino = 14, i_size = 4294967296 offset:0, len:4294967296, advise:3
 page_cache_sync_ra: dev=252:16 ino=e index=0 req_count=2048 order=0 size=0 async_size=0 ra_pages=2048 mmap_miss=0 prev_pos=-1
 page_cache_ra_order: dev=252:16 ino=e index=0 order=0 size=2048 async_size=1024 ra_pages=2048
 page_cache_sync_ra: dev=252:16 ino=e index=2048 req_count=2048 order=0 size=2048 async_size=1024 ra_pages=2048 mmap_miss=0 prev_pos=-1
 page_cache_ra_unbounded: dev=252:16 ino=e index=2048 nr_to_read=2048 lookahead_size=0
 page_cache_sync_ra: dev=252:16 ino=e index=4096 req_count=2048 order=0 size=2048 async_size=1024 ra_pages=2048 mmap_miss=0 prev_pos=-1
 page_cache_ra_unbounded: dev=252:16 ino=e index=4096 nr_to_read=2048 lookahead_size=0
 page_cache_sync_ra: dev=252:16 ino=e index=6144 req_count=2048 order=0 size=2048 async_size=1024 ra_pages=2048 mmap_miss=0 prev_pos=-1
 page_cache_ra_unbounded: dev=252:16 ino=e index=6144 nr_to_read=2048 lookahead_size=0
 page_cache_sync_ra: dev=252:16 ino=e index=8192 req_count=2048 order=0 size=2048 async_size=1024 ra_pages=2048 mmap_miss=0 prev_pos=-1
 page_cache_ra_unbounded: dev=252:16 ino=e index=8192 nr_to_read=2048 lookahead_size=0
 page_cache_sync_ra: dev=252:16 ino=e index=10240 req_count=2048 order=0 size=2048 async_size=1024 ra_pages=2048 mmap_miss=0 prev_pos=-1
 page_cache_ra_unbounded: dev=252:16 ino=e index=10240 nr_to_read=2048 lookahead_size=0
 ...
 page_cache_ra_unbounded: dev=252:16 ino=e index=1042432 nr_to_read=2048 lookahead_size=0
 page_cache_sync_ra: dev=252:16 ino=e index=1044480 req_count=2048 order=0 size=2048 async_size=1024 ra_pages=2048 mmap_miss=0 prev_pos=-1
 page_cache_ra_unbounded: dev=252:16 ino=e index=1044480 nr_to_read=2048 lookahead_size=0
 page_cache_sync_ra: dev=252:16 ino=e index=1046528 req_count=2048 order=0 size=2048 async_size=1024 ra_pages=2048 mmap_miss=0 prev_pos=-1
 page_cache_ra_unbounded: dev=252:16 ino=e index=1046528 nr_to_read=2048 lookahead_size=0

Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
---
 mm/readahead.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/mm/readahead.c b/mm/readahead.c
index c0db049a5b7b..5beaf7803554 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -340,6 +340,7 @@ void force_page_cache_ra(struct readahead_control *ractl,
 		unsigned long nr_to_read)
 {
 	struct address_space *mapping = ractl->mapping;
+	struct inode *inode = mapping->host;
 	struct backing_dev_info *bdi = inode_to_bdi(mapping->host);
 	unsigned long this_chunk;
 
@@ -352,11 +353,19 @@ void force_page_cache_ra(struct readahead_control *ractl,
 	this_chunk = max_t(unsigned long, bdi->io_pages, ractl->ra->ra_pages);
 
 	while (nr_to_read) {
-		this_chunk = min_t(unsigned long, this_chunk, nr_to_read);
+		unsigned long index = readahead_index(ractl);
+		pgoff_t end_index = (i_size_read(inode) - 1) >> PAGE_SHIFT;
 
-		if (do_page_cache_ra(ractl, this_chunk, 0))
+		if (index > end_index)
 			break;
 
+		if (nr_to_read > end_index - index)
+			nr_to_read = end_index - index + 1;
+
+		this_chunk = min_t(unsigned long, this_chunk, nr_to_read);
+
+		page_cache_sync_ra(ractl, this_chunk);
+
 		nr_to_read -= this_chunk;
 	}
 }
@@ -573,7 +582,7 @@ void page_cache_sync_ra(struct readahead_control *ractl,
 
 	/* be dumb */
 	if (do_forced_ra) {
-		force_page_cache_ra(ractl, req_count);
+		do_page_cache_ra(ractl, req_count, 0);
 		return;
 	}
 
-- 
2.52.0.107.ga0afd4fd5b-goog