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Subject(reiserfs) Re: More on 2.2.18pre2aa2
On Mon, Sep 11, 2000 at 08:15:15AM -0400, Chris Mason wrote:
> LFS changes for filldir, reiserfs_readpage, and adds limit checking in
> file_write to make sure we don't go above 2GB (Andi Kleen). Also fixes
> include/linux/fs.h, which does not patch cleanly for 3.5.25 because of usb.
>
> Note, you might see debugging messages about items moving during
> copy_from_user. These are safe, but I'm leaving them in for now as I'd
> like to find out why copy_from_user is suddenly scheduling much more than
> it used to.

That's easy to explain. Andrea's latest aa contains some low latency
patches, which add a if (current->need_resched) schedule() to copy*user
to avoid bad schedule latencies for big copies. The result is that you
see a lot more schedules, everytime the copy*user happens to hit the
end of a time slice.

BTW, there is a another optimization that could help reiserfs a lot
on SMP settings: do a unlock_kernel()/lock_kernel() around the user
copies. It is quite legal to do that (you have to handle sleeping
anyways in case of a page fault), and it allows CPUs to run in parallel
for long running copies.


-Andi


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