On Fri, Jul 08, 2022 at 03:39:38PM +0200, Jan Beulich wrote: > While in principle possible also under other conditions as long as other > parallel operations potentially consuming memory aren't "locked out", in > particular with IOMMU large page mappings used in Dom0 (for PV when in > strict mode; for PVH when not sharing page tables with HAP) ballooning > out of individual pages can actually lead to less free memory available > afterwards. This is because to split a large page, one or more page > table pages are necessary (one per level that is split). > > When rebooting a guest I've observed freemem() to fail: A single page > was required to be ballooned out (presumably because of heap > fragmentation in the hypervisor). This ballooning out of a single page > of course went fast, but freemem() then found that it would require to > balloon out another page. This repeating just another time leads to the > function to signal failure to the caller - without having come anywhere > near the designated 30s that the whole process is allowed to not make > any progress at all. > > Convert from a simple retry count to actually calculating elapsed time, > subtracting from an initial credit of 30s. Don't go as far as limiting > the "wait_secs" value passed to libxl_wait_for_memory_target(), though. > While this leads to the overall process now possibly taking longer (if > the previous iteration ended very close to the intended 30s), this > compensates to some degree for the value passed really meaning "allowed > to run for this long without making progress". > > Signed-off-by: Jan Beulich <jbeul...@suse.com> > --- > I further wonder whether the "credit expired" loop exit wouldn't better > be moved to the middle of the loop, immediately after "return true". > That way having reached the goal on the last iteration would be reported > as success to the caller, rather than as "timed out".
That would sound like a good improvement to the patch. Thanks, -- Anthony PERARD
