linux-ext4 - Re: [Bug 15910] zero-length files and performance degradation

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Message-ID: <20100510143433.GS18762@thunk.org>
Date:	Mon, 10 May 2010 10:34:33 -0400
From:	tytso@....edu
To:	Peng Tao <bergwolf@...il.com>
Cc:	bugzilla-daemon@...zilla.kernel.org, linux-ext4@...r.kernel.org
Subject: Re: [Bug 15910] zero-length files and performance degradation

On Mon, May 10, 2010 at 10:22:47PM +0800, Peng Tao wrote:
> What about letting fsync() on dir recursively fsync() all
> files/sub-dirs in the dir?
> Then apps can unpack package in a temp dir, fsync(), and rename.

There are programs to do who execute fsync() on a directory, and they
do not expect a recursive fsync() on all files/subdirectories in a
directory.

At least for Linux, sync() is synchronous and will do what you want.
There is unfortunately not a portable way to do what you want short of
fsync'ing all of the files after they are written.  This case is
mostly optimized under ext3/4 (we could do a bit better for ext4, but
the performance shouldn't be disastrous --- certainly much better than
write a file, fsync, rename a file, repeat).

					- Ted
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