[PATCH 3/3] mm/readahead: try to allocate high order pages for FADVISE_FAV_WILLNEED

[Jaegeuk Kim <jaegeuk@kernel.org>]

This patch assigns the max folio order for readahead. After applying this patch,
it starts with high-order page allocation successfully as shown in the below
traces.

Before:
 f2fs_fadvise: dev = (252,16), ino = 14, i_size = 4294967296 offset:0, len:536870912, 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=129024 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=129024 nr_to_read=2048 lookahead_size=0

After:
 f2fs_fadvise: dev = (252,16), ino = 14, i_size = 4294967296 offset:0, len:536870912, 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=9 size=2048 async_size=1024 ra_pages=2048
 page_cache_sync_ra: dev=252:16 ino=e index=2048 req_count=2048 order=9 size=2048 async_size=1024 ra_pages=2048 mmap_miss=0 prev_pos=-1
 page_cache_ra_order: dev=252:16 ino=e index=2048 order=9 size=2048 async_size=1024 ra_pages=2048
 page_cache_sync_ra: dev=252:16 ino=e index=4096 req_count=2048 order=9 size=2048 async_size=1024 ra_pages=2048 mmap_miss=0 prev_pos=-1
 page_cache_ra_order: dev=252:16 ino=e index=4096 order=9 size=2048 async_size=1024 ra_pages=2048
 page_cache_sync_ra: dev=252:16 ino=e index=6144 req_count=2048 order=9 size=2048 async_size=1024 ra_pages=2048 mmap_miss=0 prev_pos=-1
 page_cache_ra_order: dev=252:16 ino=e index=6144 order=9 size=2048 async_size=1024 ra_pages=2048
 page_cache_sync_ra: dev=252:16 ino=e index=8192 req_count=2048 order=9 size=2048 async_size=1024 ra_pages=2048 mmap_miss=0 prev_pos=-1
...
 page_cache_sync_ra: dev=252:16 ino=e index=129024 req_count=2048 order=9 size=2048 async_size=1024 ra_pages=2048 mmap_miss=0 prev_pos=-1
 page_cache_ra_order: dev=252:16 ino=e index=129024 order=9 size=2048 async_size=1024 ra_pages=2048

Cc: linux-mm@kvack.org
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
---
 mm/readahead.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/mm/readahead.c b/mm/readahead.c
index 54c78f8276fe..cfc63f7d5e81 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -593,7 +593,8 @@ void page_cache_sync_ra(struct readahead_control *ractl,
 	 * trivial case: (index - prev_index) == 1
 	 * unaligned reads: (index - prev_index) == 0
 	 */
-	if (!index || req_count > max_pages || index - prev_index <= 1UL) {
+	if (!index || req_count > max_pages || index - prev_index <= 1UL ||
+	    mapping_large_folio_support(ractl->mapping)) {
 		ra->start = index;
 		ra->size = get_init_ra_size(req_count, max_pages);
 		ra->async_size = ra->size > req_count ? ra->size - req_count :
@@ -627,7 +628,7 @@ void page_cache_sync_ra(struct readahead_control *ractl,
 	ra->size = min(contig_count + req_count, max_pages);
 	ra->async_size = 1;
 readit:
-	ra->order = 0;
+	ra->order = mapping_max_folio_order(ractl->mapping);
 	ractl->_index = ra->start;
 	page_cache_ra_order(ractl, ra);
 }
-- 
2.52.0.107.ga0afd4fd5b-goog