On Mon, Jul 07, 2025 at 04:23:19PM +0200, Pankaj Raghav (Samsung) wrote:
> From: Pankaj Raghav <p.raghav@xxxxxxxxxxx>
>
> Use largest_zero_folio() in __blkdev_issue_zero_pages().
>
> On systems with CONFIG_STATIC_PMD_ZERO_PAGE enabled, we will end up
> sending larger bvecs instead of multiple small ones.
>
> Noticed a 4% increase in performance on a commercial NVMe SSD which does
> not support OP_WRITE_ZEROES. The device's MDTS was 128K. The performance
> gains might be bigger if the device supports bigger MDTS.
>
> Signed-off-by: Pankaj Raghav <p.raghav@xxxxxxxxxxx>
> ---
> block/blk-lib.c | 17 ++++++++++-------
> 1 file changed, 10 insertions(+), 7 deletions(-)
>
> diff --git a/block/blk-lib.c b/block/blk-lib.c
> index 4c9f20a689f7..70a5700b6717 100644
> --- a/block/blk-lib.c
> +++ b/block/blk-lib.c
> @@ -196,6 +196,10 @@ static void __blkdev_issue_zero_pages(struct block_device *bdev,
> sector_t sector, sector_t nr_sects, gfp_t gfp_mask,
> struct bio **biop, unsigned int flags)
> {
> + struct folio *zero_folio;
> +
> + zero_folio = largest_zero_folio();
Just assign this in the decl :)
> +
> while (nr_sects) {
> unsigned int nr_vecs = __blkdev_sectors_to_bio_pages(nr_sects);
> struct bio *bio;
> @@ -208,15 +212,14 @@ static void __blkdev_issue_zero_pages(struct block_device *bdev,
> break;
>
> do {
> - unsigned int len, added;
> + unsigned int len;
>
> - len = min_t(sector_t,
> - PAGE_SIZE, nr_sects << SECTOR_SHIFT);
> - added = bio_add_page(bio, ZERO_PAGE(0), len, 0);
> - if (added < len)
> + len = min_t(sector_t, folio_size(zero_folio),
> + nr_sects << SECTOR_SHIFT);
> + if (!bio_add_folio(bio, zero_folio, len, 0))
Hmm, will this work if nr_sects << SECTOR_SHIFT size isn't PMD-aligned?
I guess it actually just copies individual pages in the folio as needed?
Does this actually result in a significant performance improvement? Do we
have numbers for this to justify the series?
> break;
> - nr_sects -= added >> SECTOR_SHIFT;
> - sector += added >> SECTOR_SHIFT;
> + nr_sects -= len >> SECTOR_SHIFT;
> + sector += len >> SECTOR_SHIFT;
> } while (nr_sects);
>
> *biop = bio_chain_and_submit(*biop, bio);
> --
> 2.49.0
>
