On Mon, 2009-03-23 at 13:58 -0400, Mathieu Desnoyers wrote: > * Masahiro Tamori (masahiro.tamori@xxxxxxxxx) wrote: > > 2009/3/21 Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxx>: > > > * Masahiro Tamori (masahiro.tamori@xxxxxxxxx) wrote: > [...] > > >> Our customer will use NFS to store trace data not storage device for > > >> embedded devices. > > >> Since newer lttng use splice() even if NFS can not support splice(), > > >> I create a patch to support to mmap of ltt-relay-alloc. > > >> > [...] > > >> ltt-relay-alloc mmap support > > >> > > >> Splice syscall does not support NFS. We can not save trace data to > > >> NFS directory. If this feature is enabled, you can use mmap() > > >> instead of splice(). > > >> > > > > > > > > > Hi Masahiro, > > > > > > Maybe we should consider implementing splice() support in NFS instead ? > > > > > > I removed the mmap support from the ltt-relay-alloc files because splice > > > is more efficient and does not require to vmap the pages. Unless there > > > is a strong argument telling what in NFS makes it impossible to > > > implement splice(), I don't really see the gain in putting back the > > > old mmap() mechanism we had. > > > > > > Maybe the NFS people will have some information about this ? > > > > > > Thanks, > > > > > > Mathieu > > > > > > > Hello Mathieu, > > > > I think that the best solution is NFS can support splice() even if > > it cannot zero copy. > > > > The splice() will be used by any other tools, hence NFS should support > > it sooner or later. > > > > If technical issue is remained to support splice() in NFS, > > we should support mmap in LTTng until the problem is resolved. > > Embedded people will want to use LTTng with NFS, > > though this is a bad choice. > > > > Thank you, > > Masahiro Tamori > > > > There was a LKML thread on NFS splice support back in 2006 : > > http://lkml.indiana.edu/hypermail/linux/kernel/0603.3/2102.html > > I don't know what happened with this ? I have tested NFS v2 and v3 and > have seen they do not support splice, but haven't tested NFSv4. > > Mathieu We do support splice reads and apparently don't support splice writes. However I don't see what has been stopping anybody from implementing the latter. In fact, it looks to me as if we should just be able to use generic_file_splice_write() as is. There is no O_APPEND support or anything that would require us to revalidate file lengths; it's just a perfectly ordinary write into the page cache... Cheers Trond -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html