On Wed, Nov 29 2017, Ian Kent wrote: > On 29/11/17 10:13, Mike Marion wrote: >> On Wed, Nov 29, 2017 at 12:17:27PM +1100, NeilBrown wrote: >> >>> How big do people see /proc/self/mount* getting? What size reads >>> does 'strace' show the various programs using to read it? >> >> We already have line counts into 5 figures. This wasn't an issue until >> the change of /etc/mtab to a link. The large count is due to our large >> direct automount maps. >> So .... 90,000 lines with a length of may 120 chars or about 10Meg. Presumably these machines would have so many gigabytes of RAM that caching a 10M mountinfo file would go unnoticed? Reading that in 128K chunks without generating bits on the fly will help a lot I suspect. We could probably ensure proper alignment by searching backwards for '\n' when deciding how much to return for a read. > > And, admittedly, the testing I was doing was with 15k+ size maps. > > Of course it's necessary to have this number of mounts to see serious > problems which is easiest to do with large direct mount maps. > > The thing that's different now is that before applications started > using /proc directly for mount table information using mount(2) > instead of mount(8) was enough to prevent the mount entries from > being added to the table seen by applications. I wonder who would notice if untriggered direct mounts quietly disappeared from /proc/mounts... I suspect systemd would, but there is a good chance it would fail-safe: assume that the mount worked. Alternately we could introduce /proc/self/mountinfo2 which doesn't list direct automounts and encourage problematic programs to use that where available. NeilBrown
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