Messages in this thread | | | Date | Thu, 26 Mar 2009 18:25:19 -0700 | From | Andrew Morton <> | Subject | Re: Linux 2.6.29 |
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On Thu, 26 Mar 2009 18:03:15 -0700 (PDT) Linus Torvalds <torvalds@linux-foundation.org> wrote:
> > > On Thu, 26 Mar 2009, Andrew Morton wrote: > > > > userspace can get closer than the kernel can. > > Andrew, that's SIMPLY NOT TRUE. > > You state that without any amount of data to back it up, as if it was some > kind of truism. It's not.
I've seen you repeatedly fiddle the in-kernel defaults based on in-field experience. That could just as easily have been done in initscripts by distros, and much more effectively because it doesn't need a new kernel. That's data.
The fact that this hasn't even been _attempted_ (afaik) is deplorable.
Why does everyone just sit around waiting for the kernel to put a new value into two magic numbers which userspace scripts could have set?
My /etc/rc.local has been tweaking dirty_ratio, dirty_background_ratio and swappiness for many years. I guess I'm just incredibly advanced.
> Everybody accepts that if you've written a 20MB file and then call > "fsync()" on it, it's going to take a while. But when you've written a 2kB > file, and "fsync()" takes 20 seconds, because somebody else is just > writing normally, _that_ is a bug. And it is actually almost totally > unrelated to the whole 'dirty_limit' thing. > > At least it _should_ be.
That's different. It's inherent JBD/ext3-ordered brain damage. Unfixable without turning the fs into something which just isn't jbd/ext3 any more. data=writeback is a workaround, with the obvious integrity issues.
The JBD journal is a massive designed-in contention point. It's why for several years I've been telling anyone who will listen that we need a new fs. Hopefully our response to all these problems will soon be "did you try btrfs?".
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