From: Duncan <1i5t5.duncan@cox.net>
To: Jim Salter <jim@jrs-s.net>
Cc: Marc MERLIN <marc@merlins.org>, linux-btrfs@vger.kernel.org
Subject: Re: btrfs-transaction blocked for more than 120 seconds
Date: Sun, 5 Jan 2014 13:44:25 -0700 [thread overview]
Message-ID: <20140105134425.22063890@ws> (raw)
In-Reply-To: <ADin1n00P0VAdqd01DioM9>
On Sun, 05 Jan 2014 08:42:46 -0500
Jim Salter <jim@jrs-s.net> wrote:
> On Jan 5, 2014 1:39 AM, Marc MERLIN <marc@merlins.org> wrote:
> >
> > On Fri, Jan 03, 2014 at 09:34:10PM +0000, Duncan wrote:
> > Yes, I got that. That why I ran btrfs defrag on the files after that
>
> Why are you trying to defrag an SSD? There's no seek penalty for
> moving between fragmented blocks, so defrag isn't really desirable in
> the first place.
[I normally try to reply directly to list but don't believe I've seen
this there yet, but got it direct-mailed so will reply-all in response.]
There's no seek penalty so the overall problem is dramatically lessened
as that's the significant part of it on spinning rust, correct, but...
SSDs do remain IOPS-bound, and tens or hundreds of thousands of extents
do exact an IOPS (as well as general extent bookkeeping) toll, too.
That's why I ended up enabling autodefrag here when I was first setting
up, even tho I'm on SSD. (Only after asking the list basically the same
question, what good it is autodefrag on SSD, tho.)
Luckily I don't happen to deal with any of the
internal-write-in-huge-files scenarios, however, and I enabled
autodefrag to cover the internal-write-in-small-file scenarios BEFORE I
started putting any data on the filesystems at all, so I'm basically
covered, here, without actually having to do chattr +C on anything.
> That doesn't change the fact that the described lockup sounds like a
> bug not a feature of course, but I think the answer to your personal
> issue on that particular machine is "don't defrag a solid state
> drive".
I now believe the lockup must be due to processing the hundreds of
thousands of extents on all those snapshots, too, in addition to doing
it on the main volume. I don't actually make very extensive use of
snapshots here anyway, so I didn't think about that aspect originally,
but that's gotta be what's throwing the real spanner in the works,
turning a possibly long but workable normal defrag (O(1)) into a lockup
scenario (O(n)) where virtually no progress is made as currently
coded.
--
Duncan - No HTML messages please, as they are filtered as spam.
"Every nonfree program has a lord, a master --
and if you use the program, he is your master." Richard Stallman
next parent reply other threads:[~2014-01-05 21:22 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <ADin1n00P0VAdqd01DioM9>
2014-01-05 20:44 ` Duncan [this message]
2013-12-31 11:46 btrfs-transaction blocked for more than 120 seconds Sulla
2014-01-01 12:37 ` Duncan
2014-01-01 20:08 ` Sulla
2014-01-02 8:38 ` Duncan
2014-01-03 1:24 ` Kai Krakow
2014-01-03 9:18 ` Duncan
2014-01-05 0:12 ` Sulla
2014-01-03 17:25 ` Marc MERLIN
2014-01-03 21:34 ` Duncan
2014-01-05 6:39 ` Marc MERLIN
2014-01-05 17:09 ` Chris Murphy
2014-01-05 17:54 ` Jim Salter
2014-01-05 19:57 ` Duncan
2014-01-05 20:44 ` Chris Murphy
2014-01-08 3:22 ` Marc MERLIN
2014-01-08 9:45 ` Duncan
2014-01-04 20:48 ` Roger Binns
2014-01-02 8:49 ` Jojo
2014-01-05 20:32 ` Chris Murphy
2014-01-05 21:17 ` Sulla
2014-01-05 22:36 ` Brendan Hide
2014-01-05 22:57 ` Roman Mamedov
2014-01-07 10:22 ` Brendan Hide
2014-01-06 0:15 ` Chris Murphy
2014-01-06 0:19 ` Chris Murphy
2014-01-05 23:48 ` Chris Murphy
2014-01-05 23:57 ` Chris Murphy
2014-01-06 0:25 ` Sulla
2014-01-06 0:49 ` Chris Murphy
[not found] ` <52CA06FE.2030802@gmx.at>
2014-01-06 1:55 ` Chris Murphy
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