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

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]

Message-ID: <20160406024031.GB7793@kmo-pixel>
Date:	Tue, 5 Apr 2016 18:40:31 -0800
From:	Kent Overstreet <kent.overstreet@...il.com>
To:	Ming Lei <ming.lei@...onical.com>
Cc:	Jens Axboe <axboe@...com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-block@...r.kernel.org, Christoph Hellwig <hch@...radead.org>,
	Eric Wheeler <bcache@...ts.ewheeler.net>,
	Sebastian Roesner <sroesner-kernelorg@...sner-online.de>,
	"4.2+" <stable@...r.kernel.org>, Shaohua Li <shli@...com>
Subject: Re: [PATCH] block: make sure big bio is splitted into at most 256
 bvecs

On Wed, Apr 06, 2016 at 10:37:05AM +0800, Ming Lei wrote:
> On Wed, Apr 6, 2016 at 10:34 AM, Kent Overstreet
> <kent.overstreet@...il.com> wrote:
> > On Wed, Apr 06, 2016 at 10:30:22AM +0800, Ming Lei wrote:
> >> Now limit.max_segments is for limiting segments from hw view, one this
> >> segment may include lots of pages/bvecs.
> >>
> >> The current bio_clone() issue is that we can't clone from one bio which
> >> includes more than 256 bvecs, maybe all these 256 bvecs belong to
> >> one same hw segment.
> >
> > So the distinction is purely a post multipage bvec thing?
> 
> Even after multipage bvec is applied, the limit for max bvecs is still needed
> for some cases like bio bounce, in which bio_clone() need to
> clone single page bvec.

s/max bvecs/max pages/?

What I meant is that until we have multipage bvecs, unless I'm missing something
max_segments is exactly what we want. After multipage bvecs, things do get more
complicated I agree.