From: NeilBrown <neilb@xxxxxxx>
Subject: mm: improve cleanup when ->readpages doesn't process all pages
If ->readpages doesn't process all the pages, then it is best to act as
though they weren't requested so that a subsequent readahead can try
again.
So:
- remove any 'ahead' pages from the page cache so they can be loaded
with ->readahead() rather then multiple ->read()s
- update the file_ra_state to reflect the reads that were actually
submitted.
This allows ->readpages() to abort early due e.g. to congestion, which
will then allow us to remove the inode_read_congested() test from
page_Cache_async_ra().
Link: https://lkml.kernel.org/r/164549983736.9187.16755913785880819183.stgit@noble.brown
Signed-off-by: NeilBrown <neilb@xxxxxxx>
Cc: Anna Schumaker <Anna.Schumaker@xxxxxxxxxx>
Cc: Chao Yu <chao@xxxxxxxxxx>
Cc: Darrick J. Wong <djwong@xxxxxxxxxx>
Cc: Ilya Dryomov <idryomov@xxxxxxxxx>
Cc: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Jeff Layton <jlayton@xxxxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Cc: Lars Ellenberg <lars.ellenberg@xxxxxxxxxx>
Cc: Miklos Szeredi <miklos@xxxxxxxxxx>
Cc: Paolo Valente <paolo.valente@xxxxxxxxxx>
Cc: Philipp Reisner <philipp.reisner@xxxxxxxxxx>
Cc: Ryusuke Konishi <konishi.ryusuke@xxxxxxxxx>
Cc: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
Cc: Wu Fengguang <fengguang.wu@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/readahead.c | 19 +++++++++++++++++--
1 file changed, 17 insertions(+), 2 deletions(-)
--- a/mm/readahead.c~mm-improve-cleanup-when-readpages-doesnt-process-all-pages
+++ a/mm/readahead.c
@@ -104,7 +104,13 @@
* for necessary resources (e.g. memory or indexing information) to
* become available. Pages in the final ``async_size`` may be
* considered less urgent and failure to read them is more acceptable.
- * They will eventually be read individually using ->readpage().
+ * In this case it is best to use delete_from_page_cache() to remove the
+ * pages from the page cache as is automatically done for pages that
+ * were not fetched with readahead_page(). This will allow a
+ * subsequent synchronous read ahead request to try them again. If they
+ * are left in the page cache, then they will be read individually using
+ * ->readpage().
+ *
*/
#include <linux/kernel.h>
@@ -226,8 +232,17 @@ static void read_pages(struct readahead_
if (aops->readahead) {
aops->readahead(rac);
- /* Clean up the remaining pages */
+ /*
+ * Clean up the remaining pages. The sizes in ->ra
+ * maybe be used to size next read-ahead, so make sure
+ * they accurately reflect what happened.
+ */
while ((page = readahead_page(rac))) {
+ rac->ra->size -= 1;
+ if (rac->ra->async_size > 0) {
+ rac->ra->async_size -= 1;
+ delete_from_page_cache(page);
+ }
unlock_page(page);
put_page(page);
}
_
