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From: Atemu <atemu.main@gmail.com>
To: Qu Wenruo <quwenruo.btrfs@gmx.com>
Cc: linux-btrfs@vger.kernel.org
Subject: Re: BUG: btrfs send: Kernel's memory usage rises until OOM kernel panic after sending ~37GiB
Date: Sun, 27 Oct 2019 11:33:40 +0100	[thread overview]
Message-ID: <CAE4GHgmW2A-2SUUw8FzgafRhQ2BoViBx2DsLigwBrrbbp=oOsw@mail.gmail.com> (raw)
In-Reply-To: <cb5f9048-919f-0ff9-0765-d5a33e58afa7@gmx.com>

> That's the problem.
>
> Deduped files caused heavy overload for backref walk.
> And send has to do backref walk, and you see the problem...

Interesting!
But should it really be able to make btrfs send use up >15GiB of RAM
and cause a kernel panic because of that? The btrfs doesn't even have
that much metadata on-disk in total.

> I'm very interested how heavily deduped the file is.

So am I, how could I get my hands on that information?

Are that particular file's extents what causes btrfs send's memory
usage to spiral out of control?

> If it's just all 0 pages, hole punching is more effective than dedupe,
> and causes 0 backref overhead.

I did punch holes into the disk images I have stored on it by mounting
and fstrim'ing them and the duperemove command I used has a flag that
ignores all 0 pages (those get compressed down to next to nothing
anyways) but it's likely that I ran duperememove once or twice before
I knew about that flag.

Is there a way to find such extents that could cause the backref walk
to overload?

Thanks,
Atemu

  reply	other threads:[~2019-10-27 10:33 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-26 17:46 BUG: btrfs send: Kernel's memory usage rises until OOM kernel panic after sending ~37GiB Atemu
2019-10-27  0:50 ` Qu Wenruo
2019-10-27 10:33   ` Atemu [this message]
2019-10-27 11:34     ` Qu Wenruo
2019-10-27 12:55       ` Atemu
2019-10-27 13:43         ` Qu Wenruo
2019-10-27 15:19           ` Atemu
2019-10-27 15:19       ` Atemu
2019-10-27 23:16         ` Qu Wenruo
2019-10-28 12:26           ` Atemu
2019-10-28 11:30         ` Filipe Manana
2019-10-28 12:36           ` Qu Wenruo
2019-10-28 12:43             ` Filipe Manana
2019-10-28 14:58               ` Martin Raiber
2019-10-28 12:44           ` Atemu
2019-10-28 13:01             ` Filipe Manana
2019-10-28 13:44               ` Atemu
2019-10-31 13:55                 ` Atemu

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