On Thu, Nov 29, 2018 at 06:41:31PM +0200, Nikolay Borisov wrote:
> extent_readpages processes all pages in the readlist in batches of 16,
> this is implemented by a single for loop but thanks to an if condition
> the loop does 2 things based on whether we've filled the batch or not.
> Additionally due to the structure of the code there is an additional
> check which deals with partial batches.
>
> Streamline all of this by explicitly using two loops. The outter one is
> used to process all pages while the inner one just fills in the batch
> of 16 (currently). Due to this new structure the code guarantees that
> all pages are processed in the loop hence the code to deal with any
> leftovers is eliminated.
>
> This also enable the compiler to inline __extent_readpages:
>
> ./scripts/bloat-o-meter fs/btrfs/extent_io.o extent_io.for
>
> add/remove: 0/1 grow/shrink: 1/0 up/down: 660/-820 (-160)
> Function old new delta
> extent_readpages 476 1136 +660
> __extent_readpages 820 - -820
> Total: Before=44315, After=44155, chg -0.36%
>
> Signed-off-by: Nikolay Borisov <nborisov@xxxxxxxx>
> ---
> fs/btrfs/extent_io.c | 37 ++++++++++++++++---------------------
> 1 file changed, 16 insertions(+), 21 deletions(-)
>
> diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
> index 8332c5f4b1c3..233f835dd6f8 100644
> --- a/fs/btrfs/extent_io.c
> +++ b/fs/btrfs/extent_io.c
> @@ -4093,43 +4093,38 @@ int extent_writepages(struct address_space *mapping,
> int extent_readpages(struct address_space *mapping, struct list_head *pages,
> unsigned nr_pages)
nr_pages becomes unused now. I've checked the MM code that calls here
and it's guaranteed that the number of list 'pages' members is same as
nr_pages.
> {
> +#define BTRFS_PAGES_BATCH 16
> +
> struct bio *bio = NULL;
> - unsigned page_idx;
> unsigned long bio_flags = 0;
> - struct page *pagepool[16];
> - struct page *page;
> + struct page *pagepool[BTRFS_PAGES_BATCH];
I don't think we need the extra define, if
struct page *pagepool[16];
...
for (nr = 0; nr < ARRAY_SIZE(pagepool) ...
Otherwise ok, nice cleanup.
Reviewed-by: David Sterba <dsterba@xxxxxxxx>
