From: Chris Mason <chris.mason@oracle.com>
To: Atila Romero <atila.alr@dpf.gov.br>
Cc: linux-btrfs@vger.kernel.org
Subject: Re: Compression of large files
Date: Wed, 27 May 2009 10:41:27 -0400 [thread overview]
Message-ID: <20090527144127.GA11706@think> (raw)
In-Reply-To: <4A1D49C1.8070903@dpf.gov.br>
On Wed, May 27, 2009 at 11:10:09AM -0300, Atila Romero wrote:
> During a file write, if the compression doesn't proves to be economical
> to a portion of the file, the whole file is marked as nocompress, and
> subsequent writes don't use compression at all. This can be seen as a
> feature, as it saves CPU in files like videos. But if the file is a dd
> image of a disk, or other types of large files, this behavior is
> undesirable, since different portions of the file will have different
> compression ratios.
> I only became aware of this after searching the source code, after
> spending some hours trying to find out why the compression wasn't
> working. This can be a really unexpected behavior for a end user who is
> looking for compression.
> The specific part of the code is at inode.c:
> 477 <#l477>
> /* flag the file so we don't compress in the future */
> 478 <#l478> btrfs_set_flag(inode, NOCOMPRESS);
>
> How about commenting line 478?
The plan is to add a flag for the file to make it always compress even
when parts of the file do not compress well.
-chris
prev parent reply other threads:[~2009-05-27 14:41 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-05-27 14:10 Compression of large files Atila Romero
2009-05-27 14:41 ` Chris Mason [this message]
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