From 2e169296603470d209d9feecbfb67b9c4cb5ca0f Mon Sep 17 00:00:00 2001
From: Jeff Layton <jlayton@kernel.org>
Date: Mon, 14 Sep 2020 13:30:36 -0400
Subject: [PATCH] ceph: have ceph_writepages_start call
pagevec_lookup_range_tag
Currently it calls pagevec_lookup_range_nr_tag(), but that may be
inefficient, as we might end up having to search several times as we get
down to looking for fewer pages to fill the array.
Thus spake Willy:
"I think ceph is misusing pagevec_lookup_range_nr_tag(). Let's suppose
you get a range which is AAAAbbbbAAAAbbbbAAAAbbbbbbbb(...)bbbbAAAA and
you try to fetch max_pages=13. First loop will get AAAAbbbbAAAAb and
have 8 locked_pages. The next call will get bbbAA and now
locked_pages=10. Next call gets AAb ... and now you're iterating your
way through all the 'b' one page at a time until you find that first A."
'A' here refers to pages that are eligible for writeback and 'b'
represents ones that aren't (for whatever reason).
Not capping the number of return pages may mean that we sometimes find
more pages than are needed, but the extra references will just get put
at the end.
Ceph is also the only caller of pagevec_lookup_range_nr_tag(), so this
change should allow us to eliminate that call as well. That will be done
in a follow-on patch.
Reported-by: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Reviewed-by: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
---
fs/ceph/addr.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)
diff --git a/fs/ceph/addr.c b/fs/ceph/addr.c
index 6ea761c84494..b03dbaa9d345 100644
--- a/fs/ceph/addr.c
+++ b/fs/ceph/addr.c
@@ -962,9 +962,8 @@ retry:
max_pages = wsize >> PAGE_SHIFT;
get_more_pages:
- pvec_pages = pagevec_lookup_range_nr_tag(&pvec, mapping, &index,
- end, PAGECACHE_TAG_DIRTY,
- max_pages - locked_pages);
+ pvec_pages = pagevec_lookup_range_tag(&pvec, mapping, &index,
+ end, PAGECACHE_TAG_DIRTY);
dout("pagevec_lookup_range_tag got %d\n", pvec_pages);
if (!pvec_pages && !locked_pages)
break;
--
2.42.0