linux-kernel - Re: next bio iters break discard?

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Mon, 13 Jan 2014 20:48:41 -0800
From:	Kent Overstreet <kmo@...erainc.com>
To:	"Martin K. Petersen" <martin.petersen@...cle.com>
Cc:	Hugh Dickins <hughd@...gle.com>, Jens Axboe <axboe@...nel.dk>,
	Shaohua Li <shli@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: next bio iters break discard?

On Mon, Jan 13, 2014 at 11:06:33PM -0500, Martin K. Petersen wrote:
> >>>>> "Kent" == Kent Overstreet <kmo@...erainc.com> writes:
> 
> Kent,
> 
> Kent> I think for discards we can deal with this easily enough -
> Kent> __blk_recalc_rq_segments() will have to special case them - but
> Kent> there's a similar (but worse) issue with WRITE_SAME, and looking
> Kent> at the code it does attempt to merge WRITE_SAME requests too.
> 
> DISCARD bios have no payload going down the stack. They get a payload
> attached in the sd driver and will therefore have a single bvec at
> completion time.
> 
> WRITE_SAME bios have a single bvec payload throughout their lifetime.
> 
> For both these types of requests we never attempt to merge the actual
> payloads. But the block range worked on may shrink or grow as the bio is
> split or merged going down the stack.
> 
> IOW, DISCARD, WRITE SAME and the impending COPY requests do not have a
> 1:1 mapping between the block range worked on and the size of any bvecs
> attached. Your recent changes must have changed the way we handled that
> in the past.

Yeah - but with WRITE_SAME bios, wouldn't we at least have to check that they're
writing the same data to merge them?
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/