On Mon, Oct 06, 2014 at 04:30:19PM +0200, Jan Kara wrote: > On Mon 06-10-14 11:33:23, Thanos Makatos wrote: > > > > Trond also had a comment that if we extended the ioctl to work for all > > > > inodes (not just blkdev) and allowed some additional flags of what > > > > needs to be invalidated, the new ioctl would be also useful to NFS > > > > userspace - see Trond's email at > > > > > > > > http://www.spinics.net/lists/linux-fsdevel/msg78917.html > > > > > > > > and the following thread. I would prefer to cover that usecase when we > > > > are introducing new invalidation ioctl. Have you considered that Thanos? > > > > > > Sure, though I don't really know how to do it. I'll start by looking at the code > > > flow when someone does " echo 3 > /proc/sys/vm/drop_caches", unless you > > > already have a rough idea how to do that. > > > > I realise I haven't clearly understood what the semantics of this new ioctl > > should be. > > > > My initial goal was to implement an ioctl that would _completely_ invalidate > > the buffer cache of a block device when there is no file-system involved. > > Unless I'm mistaken the patch I posted achieves this goal. > Yes. > > > We now want to extend this patch to take care of cached metadata, which seems > > to be of particular importance for NFS, and I suspect that this piece of > > functionality will still be applicable to any kind of file-system, correct? > So most notably they want the ioctl to work not only for block devices > but also for any regular file. That's easily doable - you just call > filemap_write_and_wait() and invalidate_inode_pages2() in the ioctl handler > for regular files. > > Also they wanted to be able to specify a range of a mapping to invalidate - > that's easily doable as well. Finally they wanted a 'flags' argument so you > can additionally ask fs to invalidate also some metadata. How invalidation > is done will be a fs specific thing and for now I guess we don't need to go > into details. NFS guys can sort that out when they decide to implement it. > So in the beginning we can just have u64 flags argument and in > it a single 'INVAL_DATA' flag meaning that invalidation of data in a given > range is requested. Later NFS guys can add further flags. Why do we need a new ioctl to do this? fadvise64() seems like it's the exact fit for "FADV_INVALIDATE_[META]DATA" flags... And before anyone shouts "posix_fadvise sucks!" note that I'm talking about adding flags to the syscall that the kernel defines, not the glibc posix wrapper.... Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
