----- Original Message ---- > From: Greg Banks <gnb@xxxxxxxxxxxxxxxxx> > To: Martin Knoblauch <knobi@xxxxxxxxxxxx> > Cc: linux-nfs list <linux-nfs@xxxxxxxxxxxxxxx>; linux-kernel@xxxxxxxxxxxxxxx > Sent: Thursday, September 18, 2008 10:45:01 AM > Subject: Re: [RFC][Resend] Make NFS-Client readahead tunable > > Martin Knoblauch wrote: > > ----- Original Message ---- > > > > > >> > >> I think having a tunable for client readahead is an excellent idea, > >> although not to solve your particular problem. The SLES10 kernel has a > >> patch which does precisely that, perhaps Neil could post it. > >> > >> I don't think there's a lot of point having both a module parameter and > >> a sysctl. > >> > >> > > > > Actually there is a good reason. The module parameter can be used to set the > new value at load time and never bother again. The sysctl is very convenient > when doing experiments. > > > You can set module parameters after module load in > /sys/module/$module/parameters. OK, one always learns new stuff :-) > > As Andrew already pointed out, the best solution would be a mount option. > Yep. > > But that seems much more involved as my workaround patch. > > > > > Yep. Seeing Andrews Mails, it might be less involved that I thought :-) Will have a look. > >> A maximum of 15 is unwise. I've found that (at least with the older > >> readahead mechanisms in SLES10) a multiple of 4 is required to preserve > >> rsize-alignment of READ rpcs to the server, which helps a lot with wide > >> RAID backends. So in SGI we tune client readahead to 16. > >> > >> > > > > 15 is the value that the Linux NFS client uses., at least since 2.6.3. > It's a silly value. I was not sure whether it was just arbitrary, or caused by some other internal limit. The definition made it look like it was somehow related to RPC_DEF_SLOT. > > As it is not tunable up to today, the comment seems moot :-) But it opens the > questions: > > > > a) should 1 be the minimum, or 0? > > > Turning off client RA entirely is potentially useful. > > b) can the backing_dev_info.ra_pages field safely be set to something higher > than 15? > > > Yes. Did I mention 16 ? You also mentioned that you do that at SGI. So, who knows whatelse there is changed :-) Anyway, thanks for the hint. > > > >> Your patch seems to have a bunch of other unrelated stuff mixed in. > >> > >> > > > > Yeah, someone already pointed out, that the Makefile hunk does not belong > there. But you say "a bunch" - anything else? > > > I rapidly scrolled past some stuff about 64bit inodes. Ahh. Now I remember... when I implemented the module parameter, I found that "enable_ino64" lacks a description. Yeah, should be a separate patch. Cheers Martin -- 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
