On Mon, Aug 24, 2020 at 03:55:06PM +0100, Matthew Wilcox (Oracle) wrote:
> Size the uptodate array dynamically to support larger pages in the
> page cache. With a 64kB page, we're only saving 8 bytes per page today,
> but with a 2MB maximum page size, we'd have to allocate more than 4kB
> per page. Add a few debugging assertions.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
> ---
> fs/iomap/buffered-io.c | 14 ++++++++++----
> 1 file changed, 10 insertions(+), 4 deletions(-)
>
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index dbf9572dabe9..844e95cacea8 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -22,18 +22,19 @@
> #include "../internal.h"
>
> /*
> - * Structure allocated for each page when block size < PAGE_SIZE to track
> + * Structure allocated for each page when block size < page size to track
> * sub-page uptodate status and I/O completions.
> */
> struct iomap_page {
> atomic_t read_count;
> atomic_t write_count;
> spinlock_t uptodate_lock;
> - DECLARE_BITMAP(uptodate, PAGE_SIZE / 512);
> + unsigned long uptodate[];
> };
>
> static inline struct iomap_page *to_iomap_page(struct page *page)
> {
> + VM_BUG_ON_PGFLAGS(PageTail(page), page);
> if (page_has_private(page))
> return (struct iomap_page *)page_private(page);
> return NULL;
Just to confirm: this vm bug check is to needed becuse we only
attach the iomap_page to the head page of a compound page?
Assuming that I've understood the above correctly:
Reviewed-by: Dave Chinner <dchinner@xxxxxxxxxx>
--
Dave Chinner
david@xxxxxxxxxxxxx
