On 7/19/2023 1:21 PM, Mikulas Patocka wrote:
> This patch implements REQ_OP_WRITE_ZEROES on brd. Write zeroes will free
> the pages just like discard, but the difference is that it writes zeroes
> to the preceding and following page if the range is not aligned on page
> boundary.
>
> Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
>
> ---
> drivers/block/brd.c | 22 ++++++++++++++++++----
> 1 file changed, 18 insertions(+), 4 deletions(-)
>
> Index: linux-2.6/drivers/block/brd.c
> ===================================================================
> --- linux-2.6.orig/drivers/block/brd.c
> +++ linux-2.6/drivers/block/brd.c
> @@ -272,7 +272,8 @@ out:
>
> void brd_do_discard(struct brd_device *brd, struct bio *bio)
> {
> - sector_t sector, len, front_pad;
> + bool zero_padding = bio_op(bio) == REQ_OP_WRITE_ZEROES;
> + sector_t sector, len, front_pad, end_pad;
>
> if (unlikely(!discard)) {
> bio->bi_status = BLK_STS_NOTSUPP;
> @@ -282,11 +283,22 @@ void brd_do_discard(struct brd_device *b
> sector = bio->bi_iter.bi_sector;
> len = bio_sectors(bio);
> front_pad = -sector & (PAGE_SECTORS - 1);
> +
> + if (zero_padding && unlikely(front_pad != 0))
> + copy_to_brd(brd, page_address(ZERO_PAGE(0)),
> + sector, min(len, front_pad) << SECTOR_SHIFT);
> +
Is it possible to create different interface for discard and write
zeroes ? I think it is a lot of logic adding on one function if everyone
else is okay please discard my comment ..
> sector += front_pad;
> if (unlikely(len <= front_pad))
> return;
> len -= front_pad;
> - len = round_down(len, PAGE_SECTORS);
> +
> + end_pad = len & (PAGE_SECTORS - 1);
> + if (zero_padding && unlikely(end_pad != 0))
> + copy_to_brd(brd, page_address(ZERO_PAGE(0)),
> + sector + len - end_pad, end_pad << SECTOR_SHIFT);
> + len -= end_pad;
> +
> while (len) {
> brd_free_page(brd, sector);
> sector += PAGE_SECTORS;
> @@ -302,7 +314,8 @@ static void brd_submit_bio(struct bio *b
> struct bio_vec bvec;
> struct bvec_iter iter;
>
> - if (bio_op(bio) == REQ_OP_DISCARD) {
> + if (bio_op(bio) == REQ_OP_DISCARD ||
> + bio_op(bio) == REQ_OP_WRITE_ZEROES) {
> brd_do_discard(brd, bio);
> goto endio;
> }
can we please use switch ? unless there is a strong need for if
which I failed to understand ...
> @@ -355,7 +368,7 @@ MODULE_PARM_DESC(max_part, "Num Minors t
>
> static bool discard = false;
> module_param(discard, bool, 0444);
> -MODULE_PARM_DESC(discard, "Support discard");
> +MODULE_PARM_DESC(discard, "Support discard and write zeroes");
>
write-zeroes and discards are both different req_op and they should have
a separate module parameter ...
> MODULE_LICENSE("GPL");
> MODULE_ALIAS_BLOCKDEV_MAJOR(RAMDISK_MAJOR);
> @@ -425,6 +438,7 @@ static int brd_alloc(int i)
> if (discard) {
> disk->queue->limits.discard_granularity = PAGE_SIZE;
> blk_queue_max_discard_sectors(disk->queue, round_down(UINT_MAX, PAGE_SECTORS));
> + blk_queue_max_write_zeroes_sectors(disk->queue, round_down(UINT_MAX, PAGE_SECTORS));
above should be moved to new module parameter write_zeroes, unless there
is a reason to use one module parameter for both req_op...
> }
>
> /* Tell the block layer that this is not a rotational device */
>
-ck
