From: A L <mail@lechevalier.se>
To: Nikolay Borisov <nborisov@suse.com>,
Hamish Moffatt <hamish-btrfs@moffatt.email>,
linux-btrfs@vger.kernel.org
Cc: linux-btrfs@vger.kernel.org
Subject: Re: new database files not compressed
Date: Wed, 2 Sep 2020 11:57:41 +0200 (GMT+02:00) [thread overview]
Message-ID: <dede53e.d98f7053.1744e402728@lechevalier.se> (raw)
In-Reply-To: <03ec55ee-5cf3-54fa-1a81-abc93006ca7b@suse.com>
---- From: Nikolay Borisov <nborisov@suse.com> -- Sent: 2020-09-02 - 07:57 ----
>>
>> I've been able to reproduce this with a trivial test program which
>> mimics the I/O behaviour of Firebird.
>>
>> It is calling fallocate() to set up a bunch of blocks and then writing
>> them with pwrite(). It seems to be the fallocate() step which is
>> preventing compression.
>>
>> Here is my trivial test program which just writes zeroes to a file. The
>> output file does not get compressed by btrfs.
>
> Ag yes, this makes sense, because fallocate creates PREALLOC extents
> which are NOCOW (since they are essentially empty so it makes no sense
> to CoW them) hence they go through a different path which doesn't
> perform compression.
>
Hi,
This is interesting. I think that a lot of applications use fallocate in their normal operations. This is probably why we see weird compsize results every now and then.
A file that is nocow will also not have checksums. Is this true for these fallocated files (that has data written to them) too?
I would really like to see that Btrfs was corrected so that writes to an fallocated area will be compressed (if one is using compression that is).
Thanks.
next prev parent reply other threads:[~2020-09-02 9:57 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-30 9:35 new database files not compressed Hamish Moffatt
2020-08-31 2:20 ` Eric Wong
2020-08-31 2:44 ` Hamish Moffatt
2020-08-31 3:15 ` A L
2020-08-31 3:47 ` Zygo Blaxell
2020-08-31 8:53 ` Hamish Moffatt
2020-08-31 9:25 ` Nikolay Borisov
2020-08-31 10:40 ` Hamish Moffatt
2020-08-31 10:47 ` Nikolay Borisov
2020-08-31 12:56 ` Hamish Moffatt
2020-08-31 11:15 ` Roman Mamedov
2020-08-31 12:54 ` Hamish Moffatt
2020-08-31 12:57 ` Nikolay Borisov
2020-08-31 23:50 ` Hamish Moffatt
2020-09-01 5:15 ` Nikolay Borisov
2020-09-01 8:55 ` Hamish Moffatt
2020-09-02 0:32 ` Hamish Moffatt
2020-09-02 5:57 ` Nikolay Borisov
2020-09-02 6:05 ` Hamish Moffatt
2020-09-02 6:10 ` Nikolay Borisov
2020-09-02 9:57 ` A L [this message]
2020-09-02 10:09 ` Nikolay Borisov
2020-09-03 15:04 ` A L
2020-09-02 16:16 ` Zygo Blaxell
2020-09-03 12:53 ` Hamish Moffatt
2020-09-03 19:44 ` Zygo Blaxell
2020-09-04 8:07 ` Hamish Moffatt
2020-09-05 4:07 ` Zygo Blaxell
2020-09-03 15:03 ` A L
2020-09-03 21:52 ` Zygo Blaxell
2020-09-01 1:43 ` Chris Murphy
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