On 11.07.2022 18:21, Anthony PERARD wrote: > 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.
Oh. I would have made it a separate one, if deemed sensible. Order shouldn't matter as I'd consider both backporting candidates. Jan
