LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Eric Wheeler <drbd-dev@lists.ewheeler.net>
To: Lars Ellenberg <lars.ellenberg@linbit.com>
Cc: drbd-dev@lists.linbit.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] drbd: fix discard_zeroes_if_aligned regression
Date: Sun, 2 Jun 2019 00:28:31 +0000 (UTC)	[thread overview]
Message-ID: <alpine.LRH.2.11.1906012121470.27699@mx.ewheeler.net> (raw)
In-Reply-To: <20190528131823.GD5803@soda.linbit>

[-- Attachment #1: Type: TEXT/PLAIN, Size: 2608 bytes --]

On Tue, 28 May 2019, Lars Ellenberg wrote:

> On Fri, May 10, 2019 at 05:36:32PM +0000, Eric Wheeler wrote:
> > Hi Lars,
> > 
> > We just tried 4.19.x and this bugs still exists. We applied the patch 
> > which was originally submitted to this thread and it still applies cleanly 
> > and seems to work for our use case. You mentioned that you had some older 
> > code which zeroed out unaligned discard requests (or perhaps it was for a 
> > different purpose) that you may be able to use to patch this. Could you 
> > dig those up and see if we can get this solved?
> > 
> > It would be nice to be able to use drbd with thin backing volumes from the 
> > vanilla kernel. If this has already been fixed in something newer than 
> > 4.19, then please point me to the commit.
> 
> I think it was merged upstream in 5.0
> f31e583aa2c2 drbd: introduce P_ZEROES (REQ_OP_WRITE_ZEROES on the "wire")

Thanks Lars, I appreciate your patch.  

Your unaligned zerout code in drbd_issue_discard_or_zero_out() looks 
great.  I particulary like how you adjusted max_discard_sectors to the 
granularity, as well as alignment handling.  Well thought out.

Your commit notes that "for backward compatibility, P_TRIM means zero-out, 
unless the DRBD_FF_WZEROES feature flag is agreed upon during handshake."

We test our environment by deploying the newer kernel on one of the DRBD 
servers and checking for regressions---but this will cause a zero-out on 
the new server because the old server doesn't yet support DRBD_FF_WZEROES.

For our purpose, can you think of any reason that it would be unsafe to 
hack the following into drbd_do_features() so the newer version will not 
zero-out while we test and get both nodes up to the newer version?

diff --git a/drivers/block/drbd/drbd_receiver.c b/drivers/block/drbd/drbd_receiver.c
index c7ad88d..76191e6 100644
--- a/drivers/block/drbd/drbd_receiver.c
+++ b/drivers/block/drbd/drbd_receiver.c
@@ -5382,6 +5382,8 @@ static int drbd_do_features(struct drbd_connection *connection)
 	connection->agreed_pro_version = min_t(int, PRO_VERSION_MAX, p->protocol_max);
 	connection->agreed_features = PRO_FEATURES & be32_to_cpu(p->feature_flags);
 
+	connection->agreed_features |= DRBD_FF_WZEROES;
+
 	drbd_info(connection, "Handshake successful: "
 	     "Agreed network protocol version %d\n", connection->agreed_pro_version);


--
Eric Wheeler



> 
> -- 
> : Lars Ellenberg
> : LINBIT | Keeping the Digital World Running
> : DRBD -- Heartbeat -- Corosync -- Pacemaker
> : R&D, Integration, Ops, Consulting, Support
> 
> DRBD® and LINBIT® are registered trademarks of LINBIT
> 

  reply	other threads:[~2019-06-02  0:28 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <15124635.GA4107@soda.linbit>
2018-01-15 23:00 ` Eric Wheeler
2018-01-16  7:26   ` Christoph Hellwig
2018-01-16  9:49     ` Lars Ellenberg
2019-05-10 17:36       ` Eric Wheeler
2019-05-28 13:18         ` Lars Ellenberg
2019-06-02  0:28           ` Eric Wheeler [this message]
2018-01-17  0:43     ` Eric Wheeler

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=alpine.LRH.2.11.1906012121470.27699@mx.ewheeler.net \
    --to=drbd-dev@lists.ewheeler.net \
    --cc=drbd-dev@lists.linbit.com \
    --cc=lars.ellenberg@linbit.com \
    --cc=linux-kernel@vger.kernel.org \
    --subject='Re: [PATCH] drbd: fix discard_zeroes_if_aligned regression' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).