From: Liu Bo <bo.li.liu@oracle.com>
To: Thorn Roby <Thorn.Roby@harlandfs.com>
Cc: "linux-btrfs@vger.kernel.org" <linux-btrfs@vger.kernel.org>
Subject: Re: Mounted compress-force=zlib, compresses when files copied in, but not when written directly by application
Date: Thu, 6 Dec 2012 14:59:15 +0800 [thread overview]
Message-ID: <20121206065914.GA5294@liubo.jp.oracle.com> (raw)
In-Reply-To: <6726B0D4C83B3047A636A714BAB0B92306C5A4@DSM-SRV-MBX2.harlandfs.com>
On Wed, Dec 05, 2012 at 05:42:51PM +0000, Thorn Roby wrote:
> My previous reply was incorrect in one point - the data is never copied from the transaction log into the sparse datafiles, instead the application writes the same data independently to both locations.
> Also, I failed to mention that the files are memmapped, and it's possible that the write operations attempt to use DIRECT_IO, which I believe is disabled by btrfs with compression - is it possible that an attempt to use DIRECT_IO or memmapped files would prevent compression?
>
Actually, writting with DIRECT_IO will fall back to buffer write for
safety, and mmap files just dirty pages, should be same with buffer
write, so it might be other reasons.
thanks,
liubo
next prev parent reply other threads:[~2012-12-06 7:00 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-12-04 19:44 Mounted compress-force=zlib, compresses when files copied in, but not when written directly by application Thorn Roby
2012-12-05 2:01 ` Liu Bo
2012-12-05 17:21 ` Thorn Roby
2012-12-05 17:42 ` Thorn Roby
2012-12-06 6:59 ` Liu Bo [this message]
2012-12-06 20:34 ` Thorn Roby
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