Messages in this thread | | | Date | Mon, 3 Apr 2006 01:27:53 -0700 | From | Andrew Morton <> | Subject | Re: [patch 1/1] sys_sync_file_range() |
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Jens Axboe <axboe@suse.de> wrote: > > 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...
Yeah. PF_SYNCWRITE was a performance tweak for the anticipatory scheduler. As cfq is using it as well now (hopefully to good effect) I guess it could be formalised more.
> > 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! :-)
I think once someone starts coding it, they'll become a big fan of PF_SYNCWRITE...
For the page writeback functions it's probably possible to use writeback_control.sync_mode=WB_SYNC_ALL as a trigger, propagate that into the IO layer. Maybe that'll always be sufficient - it's hard to tell. The writeback paths are twisty and deep...
Then again, using WB_SYNC_ALL as a hint that this process will be waiting for this writeout to complete is a bit hacky too - it doesn't _really_ mean that - it just means that I/O should be _started_ against all relevant dirty data.
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