On Tue, Oct 20, 2020 at 02:43:57AM +0100, Matthew Wilcox wrote:
> I think the easiest way to fix this is to decline to allocate readahead
> pages beyond EOF. That is, if we have a file which is, say, 61 pages
> long, read the last 5 pages into an order-2 THP and an order-0 THP
> instead of allocating an order-3 THP and zeroing the last three pages.
Oh yeah, really easy.
+++ b/mm/readahead.c
@@ -481,6 +481,11 @@ void page_cache_ra_order(struct readahead_control *ractl,
if (order == 1)
order = 0;
}
+ /* Don't allocate pages past EOF */
+ while (index + (1UL << order) - 1 > limit) {
+ if (--order == 1)
+ order = 0;
+ }
err = ra_alloc_page(ractl, index, mark, order, gfp);
if (err)
break;
I've added that to an earlier patch and I've pushed out commit
cd3fa4bc6516 as the head of
http://git.infradead.org/users/willy/pagecache.git/shortlog
