On 12.07.2022 09:01, Jan Beulich wrote: > 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.
Except, of course, if the change here is controversial or needs a lot of further refinement, in which case the other one may better go first. Please let me know ... Jan
