Re: [PATCH v3] block: make sure big bio is splitted into at most 256 bvecs

On Mon, Aug 22, 2016 at 1:58 AM, Kent Overstreet
[off-list ref] wrote:

On Sun, Aug 21, 2016 at 05:31:33PM +0800, Ming Lei wrote:

quoted

This patch is definitely correct, and I don't see dealing with 'no_merge'
should be removed.

In this case, the bio is still possible to merge with others because
it doesn't violate any limit of the queue because it just can't be held in
256 bvecs, that means it is correct to clear no_merge for this situation.

Also I don't think it is complicated or ugly to deal with the flag.

It's extra unnecessary code. All other things being equal, less code is always
better than more code. It works just fine without it, what's the justification
for adding the flag?

From rationality view, the 'no_merge' flag need to be cleared because

it doesn't violate any queue's limit and should be allowed to merge, and
actually it is possible to submit all these splitted bios into hardware via
one request, that is different with other splitting cases.

Given you introduced support of arbitrarily sized bios in commit 54efd50bf
(block:make generic_make_request handle arbitrarily sized bios), other
drivers/fs might use this to simplify bio submission too in the future.

Don't be so dismissive of other maintainer's concerns, we've got to deal with
this code too. Especially when I and Christoph are agreeing on something - how
often does that happen?

OK, I will submit a V4 and comment on not merging just for simplicity resaon.


Thanks,
Ming