Re: RFC: multiple concurrent I/O ops for copy_file_range(2)

On Sat, Sep 03, 2022 at 03:11:03AM +0000, Rick Macklem wrote:
> Hi,
> 
> A recent discussion involving copy_file_range(2) performance
> included a suggestion that, maybe, copying of subranges
> should be done concurrently.
> 
> Although I cannot be 100% sure, I think that this would
> involve using multiple kernel threads (taskqueue or similar)
> to issue I/O operations on the file system(s) for blocks
> (of f_iosize maybe?) concurrently, to improve performance.
> 
> Doing this in a system call is unusual, to say the least but, then,
> copy_file_range(2) is an unusual system call to begin with.
> 
> I have not attempted to code this up as of yet.
> 
> So, what do others think of this idea?
> 
Note that UFS does not understand more than one stream of writes to
single vnode.  The result could be a severe fragmentation, which is
relevant even for SSDs (due to large internal block size).