On Wed, Feb 19, 2020 at 08:12:23PM -0600, Eric Sandeen wrote: > > > On 2/19/20 6:17 PM, Luis Chamberlain wrote: > > On Wed, Feb 19, 2020 at 02:01:04PM -0800, Darrick J. Wong wrote: > >> On Wed, Feb 19, 2020 at 05:55:02PM +0000, Luis Chamberlain wrote: > >>> On Wed, Feb 19, 2020 at 09:09:45AM -0800, Darrick J. Wong wrote: > >>>> On Wed, Feb 19, 2020 at 02:38:24PM +0000, Luis Chamberlain wrote: > >>>>> On Wed, Feb 19, 2020 at 03:32:27PM +0100, Carlos Maiolino wrote: > >>>>>> On Wed, Feb 19, 2020 at 01:57:15PM +0000, Luis Chamberlain wrote: > >>>>>>> I hear some folks still use CONFIG_XFS_RT, I was curious what was the > >>>>>>> actual modern typical use case for it. I thought this was somewhat > >>>>>>> realted to DAX use but upon a quick code inspection I see direct > >>>>>>> realtionship. > >>>>>> > >>>>>> Hm, not sure if there is any other use other than it's original purpose of > >>>>>> reducing latency jitters. Also XFS_RT dates way back from the day DAX was even a > >>>>>> thing. But anyway, I don't have much experience using XFS_RT by myself, and I > >>>>>> probably raised more questions than answers to yours :P > >>>>> > >>>>> What about another question, this would certainly drive the users out of > >>>>> the corners: can we remove it upstream? > >>>> > >>>> My DVR and TV still use it to record video data. > >>> > >>> Is anyone productizing on that though? > >>> > >>> I was curious since most distros are disabling CONFIG_XFS_RT so I was > >>> curious who was actually testing this stuff or caring about it. > >> > >> Most != All. We enabled it here, for development of future products. > > > > Ah great to know, thanks! > > > >>>> I've also been pushing the realtime volume for persistent memory devices > >>>> because you can guarantee that all the expensive pmem gets used for data > >>>> storage, that the extents will always be perfectly aligned to large page > >>>> sizes, and that fs metadata will never defeat that alignment guarantee. > >>> > >>> For those that *are* using XFS in production with realtime volume with dax... > >>> I wonder whatcha doing about all these tests on fstests which we don't > >>> have a proper way to know if the test succeeded / failed [0] when an > >>> external logdev is used, this then applies to regular external log dev > >>> users as well [1]. > >> > >> Huh? How did we jump from realtime devices to external log files? > > > > They share the same problem with fstests when using an alternative log > > device, which I pointed out on [0] and [1]. > > > > [0] https://github.com/mcgrof/oscheck/blob/master/expunges/linux-next-xfs/xfs/unassigned/xfs_realtimedev.txt > > [1] https://github.com/mcgrof/oscheck/blob/master/expunges/linux-next-xfs/xfs/unassigned/xfs_logdev.txt > > > >>> Which makes me also wonder then, what are the typical big users of the > >>> regular external log device? > >>> > >>> Reviewing a way to address this on fstests has been on my TODO for > >>> a while, but it begs the question of how much do we really care first. > >>> And that's what I was really trying to figure out. > >>> > >>> Can / should we phase out external logdev / realtime dev? Who really is > >>> caring about this code these days? > >> > >> Not many, I guess. :/ > >> > >> There seem to be a lot more tests these days that use dmflakey on the > >> data device to simulate a temporary disk failure... but those aren't > >> going to work for external log devices because they seem to assume that > >> what we call the data device is also the log device. > > > > That goes to show that the fstests assumption on a shared data/log device was > > not only a thing of the past, its still present, and unless we address > > soon, the gap will only get bigger. > > > > OK thanks for the feedback. The situation in terms of testing rtdev or > > external logs seems actually worse than I expected given the outlook for > > the future and no one seeming to really care too much right now. If the > > dax folks didn't care, then the code will likely just bit rot even more. > > Is it too nutty for us to consider removing it as a future goal? > > Less nutty would be to analyze the failures and fix the tests. > > Here's a start, I'll send this one to fstests. > > diff --git a/common/repair b/common/repair > index 5a9097f4..cf69dde9 100644 > --- a/common/repair > +++ b/common/repair > @@ -9,8 +9,12 @@ _zero_position() > value=$1 > struct="$2" > > + SCRATCH_OPTIONS="" > + [ "$USE_EXTERNAL" = yes -a ! -z "$SCRATCH_LOGDEV" ] && \ > + SCRATCH_OPTIONS="-l$SCRATCH_LOGDEV" > + > # set values for off/len variables provided by db > - eval `xfs_db -r -c "$struct" -c stack $SCRATCH_DEV | perl -ne ' > + eval `xfs_db -r -c "$struct" -c stack $SCRATCH_OPTIONS $SCRATCH_DEV | perl -ne ' > if (/byte offset (\d+), length (\d+)/) { > print "offset=$1\nlength=$2\n"; exit > }'` > diff --git a/tests/xfs/030 b/tests/xfs/030 > index efdb6a18..e1cc32ef 100755 > --- a/tests/xfs/030 > +++ b/tests/xfs/030 > @@ -77,7 +77,10 @@ else > _scratch_unmount > fi > clear="" > -eval `xfs_db -r -c "sb 1" -c stack $SCRATCH_DEV | perl -ne ' > +SCRATCH_OPTIONS="" > +[ "$USE_EXTERNAL" = yes -a ! -z "$SCRATCH_LOGDEV" ] && \ > + SCRATCH_OPTIONS="-l$SCRATCH_LOGDEV" > +eval `xfs_db -r -c "sb 1" -c stack $SCRATCH_OPTIONS $SCRATCH_DEV | perl -ne ' _scratch_xfs_db --D > if (/byte offset (\d+), length (\d+)/) { > print "clear=", $1 / 512, "\n"; exit > }'` > > >
