linux-kernel - Re: [GIT PULL] DRBD bits for 2.6.39

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: <4D78CF3A.7000408@kernel.dk>
Date:	Thu, 10 Mar 2011 14:16:42 +0100
From:	Jens Axboe <axboe@...nel.dk>
To:	Philipp Reisner <philipp.reisner@...bit.com>
CC:	linux-kernel@...r.kernel.org, drbd-dev@...ts.linbit.com
Subject: Re: [GIT PULL] DRBD bits for 2.6.39

On 2011-03-10 13:10, Philipp Reisner wrote:
> [...]
>>
>> Now that I have your attention... Did you look at the plugging changes?
> 
> You always have it :)
> I looked at the changes, and I noticed that we no longer get the unplug
> events. 
> 
>> As Christoph mentioned, you seem to be passing plugging information on
>> the wire. What is the reason for that? With the on-stack plugging, these
>> events are not seen by the block device anymore.
>>
> 
> Imagine DRBD in synchronous mode (protocol C in DRBD speak) on an older
> kernel. We mirror a write, in order to get the write-ack packet from the
> peer, the peer needs to unplug as well. -> Send the unplug events via the
> wire.
> 
> Now, it we would connect a current-head-of-git DRBD on one node to
> a older one (which still needs unplug packets to respond quickly),
> we would have a tar pit block device. (At least for single synchronous
> writes)
> 
> We are in brainstorming mode right now here.
> One idea is to have a timer, that gets touched with every request we get
> in, in case it expires, we send out a unplug event over the wire.
> 
> But having the unplug events would be more elegant of course...

The unplug is essentially the ->request_fn() being run now. So for older
clients you could just always include an unplug even when you pulled
whatever off the queue there is and sent it to the device.

-- 
Jens Axboe

--
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/