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 ' if (/byte offset (\d+), length (\d+)/) { print "clear=", $1 / 512, "\n"; exit }'`
