Re: [f2fs-dev] write performance difference 3.18.21/4.2.1

[Jaegeuk K. <ja...@ke...>]

On Fri, Sep 25, 2015 at 05:47:12PM +0800, Chao Yu wrote:
> Hi Marc Jaegeuk,
> 
> > -----Original Message-----
> > From: Marc Lehmann [mailto:sc...@sc...]
> > Sent: Friday, September 25, 2015 2:51 PM
> > To: Jaegeuk Kim
> > Cc: lin...@li...
> > Subject: Re: [f2fs-dev] write performance difference 3.18.21/4.2.1
> > 
> > On Thu, Sep 24, 2015 at 11:28:36AM -0700, Jaegeuk Kim <ja...@ke...> wrote:
> > > One thing that we can try is to run the latest f2fs source in v3.18.
> > > This branch supports f2fs for v3.18.
> > 
> > Ok, please bear with me, the last time I built my own kernel was during
> > the 2.4 timeframe, and this is a ubuntu kernel. What I did is this:
> > 
> >    git clone -b linux-3.18 git://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs.git
> >    cd f2fs/fs/f2fs
> >    rsync -avPR include/linux/f2fs_fs.h include/trace/events/f2fs.h
> > /usr/src/linux-headers-3.18.21-031821/.
> >    make -C /lib/modules/3.18.21-031821-generic/build/ M=$PWD modules modules_install
> > 
> > I then rmmod f2fs/insmod the resulting module, and tried to mount my
> > existing f2fs fs for a quick test, but got a null ptr exception on "mount":
> > 
> > http://ue.tst.eu/e4628dcee97324e580da1bafad938052.txt
> 
> This is my fault, sorry about introducing this oops. :(
> 
> Please revert the commit 7c5e466755ff ("f2fs: readahead cp payload
> pages when mount") since in this commit we try to access invalid
> SIT_I(sbi)->sit_base_addr which should be inited later.

Oops, I'll just remove this patch which was not going too far away.

Thanks,

> 
> Thanks,
> 
> > 
> > Probably caused me not building a full kernel, but recreating how ubuntu
> > build their kernels on a debian system isn't something I look forward to.
> > 
> > > For example, if I can represent blocks like:
> > [number of logs discussion]
> > 
> > Thanks for this explanation - two logs doesn't look so bad, from a
> > locality viewpoint (not a big issue for flash, but a big issue for
> > rotational devices - I also realised I can't use dmcache as dmcache, even
> > in writethrough mode, writes back all data after an unclean shutdown,
> > which would positively kill the disk).
> > 
> > Since whatever speed difference I saw with two logs wasn't big, you
> > completely sold me on 6 logs, or 4 (especially if it seepds up the gc,
> > which I haven't much tested yet). Two logs was merely a test anyway (the
> > same with no_heap, I don't know what it does, but I thought it is worth
> > a try, as metadata + data nearer together is better than having them at
> > opposite ends of the log or so).
> > 
> > --
> >                 The choice of a       Deliantra, the free code+content MORPG
> >       -----==-     _GNU_              http://www.deliantra.net
> >       ----==-- _       generation
> >       ---==---(_)__  __ ____  __      Marc Lehmann
> >       --==---/ / _ \/ // /\ \/ /      sc...@sc...
> >       -=====/_/_//_/\_,_/ /_/\_\
> > 
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