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SubjectRe: [PATCH] dm-verity:unnecessary data blocks that need not read hash blocks
On Tue, Jan 07, 2020 at 10:48:43AM +0800, zhou_xianrong wrote:

> Subject: [PATCH] dm-verity:unnecessary data blocks that need not read

Please use a proper commit subject. It should begin with "dm verity: " and use
the imperative tense to describe the change, e.g.

dm verity: don't prefetch hash blocks for already-verified data

Also this should have been "PATCH v2", not simply PATCH, since you already sent
out a previous version.

You also sent out multiple copies of this email for some reason, so I just chose
one arbitrarily to reply to...

> diff --git a/drivers/md/dm-verity-target.c b/drivers/md/dm-verity-target.c
> index 4fb33e7..4127711 100644
> --- a/drivers/md/dm-verity-target.c
> +++ b/drivers/md/dm-verity-target.c
> @@ -611,8 +611,27 @@ static void verity_prefetch_io(struct work_struct *work)
>
> static void verity_submit_prefetch(struct dm_verity *v, struct dm_verity_io *io)
> {
> + sector_t block = io->block;
> + unsigned int n_blocks = io->n_blocks;
> struct dm_verity_prefetch_work *pw;
>
> + if (v->validated_blocks) {
> + while (n_blocks) {
> + if (unlikely(!test_bit(block, v->validated_blocks)))
> + break;
> + block++;
> + n_blocks--;
> + }
> + while (n_blocks) {
> + if (unlikely(!test_bit(block + n_blocks - 1,
> + v->validated_blocks)))
> + break;
> + n_blocks--;
> + }
> + if (!n_blocks)
> + return;
> + }

This looks fine now, though it's a bit more verbose than necessary, and I don't
think unlikely() will make any difference here. Consider simplifying it to:

if (v->validated_blocks) {
while (n_blocks && test_bit(block, v->validated_blocks)) {
block++;
n_blocks--;
}
while (n_blocks && test_bit(block + n_blocks - 1,
v->validated_blocks))
n_blocks--;
if (!n_blocks)
return;
}

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