Re: [patch 1/1] sys_sync_file_range()

[Jens Axboe <axboe@suse.de>]

On Mon, Apr 03 2006, Neil Brown wrote:
> On Friday March 31, nathans@sgi.com wrote:
> > On Thu, Mar 30, 2006 at 06:58:46PM +1100, Neil Brown wrote:
> > > On Wednesday March 29, akpm@osdl.org wrote:
> > > > Remove the recently-added LINUX_FADV_ASYNC_WRITE and LINUX_FADV_WRITE_WAIT
> > > > fadvise() additions, do it in a new sys_sync_file_range() syscall
> > > > instead. 
> > > 
> > > Hmmm... any chance this could be split into a sys_sync_file_range and
> > > a vfs_sync_file_range which takes a 'struct file*' and does less (or
> > > no) sanity checking, so I can call it from nfsd?
> > > 
> > > Currently I implement COMMIT (which has a range) with a by messing
> > > around with filemap_fdatawrite and filemap_fdatawait (ignoring the
> > > range) and I'd rather than a vfs helper.
> > 
> > I'm not 100% sure, but it looks like the PF_SYNCWRITE process flag
> > should be set on the nfsd's while they're doing that, which doesn't
> > seem to be happening atm.  Looks like a couple of the IO schedulers
> > will make use of that knowledge now.  All the more reason for a VFS
> > helper here I guess. ;)
> 
> PF_SYNCWRITE? What's that???
> 
> (find | xargs grep ...)
> Oh.  The block device schedulers like to know if a request is sync or
> async (and all reads are assumed to be sync) - which is reasonable -
> and so have a per-task flag to tell them - which isn't (IMO).
> 
> md/raid (particularly raid5) often does the write from a different
> process than generated the original request, so that will break
> completely. 

I don't think any disagrees with you, the sync-write process flag is
indeed an atrocious beast...

> What is wrong with a bio flag I wonder....

Nothing, in fact I would love for it to be changed. I'm sure such a
patch would be accepted with open arms! :-)

-- 
Jens Axboe