Re: write performance difference 3.18.21/git f2fs

From: Marc Lehmann <schmorp@schmorp.de>
To: Jaegeuk Kim <jaegeuk@kernel.org>
Cc: linux-f2fs-devel@lists.sourceforge.net
Subject: Re: write performance difference 3.18.21/git f2fs
Date: Sat, 26 Sep 2015 15:59:57 +0200	[thread overview]
Message-ID: <20150926135957.GB9860@schmorp.de> (raw)
In-Reply-To: <20150926075253.GD13619@jaegeuk-mac02.hsd1.ca.comcast.net>

On Sat, Sep 26, 2015 at 12:52:53AM -0700, Jaegeuk Kim <jaegeuk@kernel.org> wrote:
> > Just for fun I'll start doing a -s64 run.

(which had the same result).

> Okay, so before finding bad commits, if possible, can you get block traces?

If you can teach me how to, sure!

In the meantime, maybe what happened is that f2fs leaves some gaps (e.g.
for alignment) when writing now, and didn't in 3.18? That would somehow
explain what I see.

Except that with the 3.18 code, there is virtually no read access while
writing to the disk for hours. With f2fs git, there is a small 16kb read
every half a minute or so, and after a while, a lot of "reading a few
mb/s, while writing a few mb/s".

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