Re: Tom Lane 2014-06-23 <17054.1403542164@sss.pgh.pa.us>
> > While I'd love to reduce the number of future installations without
> > this fix in place, I respect the decision to honor project policy. At
> > the same time, this change does not break anything. It introduces new
> > environment variables which change the behaviour, but behaves the old
> > way in the absence of those variables.
>
> Uh, no, it doesn't. We removed the dependence on -DLINUX_OOM_SCORE_ADJ.
> If a packager is expecting that to still work in 9.4, he's going to be
> unpleasantly surprised, because the system will silently fail to do what
> he's expecting: it will run all the backend processes at no-OOM-kill
> priority, which is likely to be bad.
Ok I'm late to the party, but the reason I'm still joining is we have
proper unit tests which just told me the 9.5 packages have changed OOM
handling. So it wouldn't just slip through if you changed that in 9.4
as well, but would get fixed.
I have two comments on the patch:
The choice to make the behavior depend first on PG_OOM_ADJUST_FILE and
only secondly on PG_OOM_ADJUST_VALUE seems the wrong way round to me.
On every modestly new kernel oom_score_adj is present, so
PG_OOM_ADJUST_FILE should default to using it. On the other hand, what
people really want to achieve (or tune) with this feature is to set
the OOM adjustment back to 0 (or some other value), so to me, it would
be much more natural to set PG_OOM_ADJUST_VALUE=0 to activate the
feature, and only have to mess with PG_OOM_ADJUST_FILE if my kernel is
older. (Which it isn't on any kernel supported by Debian and Ubuntu
LTS.)
The other bit is the non-deprecation of OOM_ADJ in
contrib/start-scripts/linux. It took me a while to understand the
logic of the variables used there - the interface would be much
clearer if it just was like this:
... set default PG_OOM_ADJUST_FILE=/proc/self/oom_score_adj
... and then this in the configurable part of the script:
PG_MASTER_OOM_SCORE_ADJ=-1000
PG_OOM_SCORE_ADJ=0
# Older Linux kernels may not have /proc/self/oom_score_adj, but instead
# /proc/self/oom_adj, which works similarly except the disable value is -17.
# For such a system, uncomment these three lines instead.
#PG_OOM_ADJUST_FILE=/proc/self/oom_adj
#PG_MASTER_OOM_SCORE_ADJ=-17
#PG_OOM_SCORE_ADJ=0
... and then use PG_OOM_ADJUST_FILE below instead of manually figuring
out which proc file to write to by looking at OOM.*_ADJ.
Christoph
--
cb@df7cb.de | http://www.df7cb.de/
