On Mon, Mar 01, 2021 at 01:43:00PM +0100, David Hildenbrand wrote: > Same experiment with ZONE_MOVABLE: > > a) Free huge pages: all memory can get unplugged again. > > b) Allocated/populated but idle huge pages: all memory can get unplugged > again. > > c) Allocated/populated but all 512 huge pages are read/written in a loop: > all memory can get unplugged again, but I get a single > > [ 121.192345] alloc_contig_range: [180000, 188000) PFNs busy > > Most probably because it happened to try migrating a huge page while it was > busy. As virtio-mem retries on ZONE_MOVABLE a couple of times, it can deal > with this temporary failure. > > > > Last but not least, I did something extreme: > > ]# cat /proc/meminfo > MemTotal: 5061568 kB > MemFree: 186560 kB > MemAvailable: 354524 kB > ... > HugePages_Total: 2048 > HugePages_Free: 2048 > HugePages_Rsvd: 0 > HugePages_Surp: 0 > > > Triggering unplug would require to dissolve+alloc - which now fails when > trying to allocate an additional ~512 huge pages (1G). > > > As expected, I can properly see memory unplug not fully succeeding. + I get > a fairly continuous stream of > > [ 226.611584] alloc_contig_range: [19f400, 19f800) PFNs busy > ... > > But more importantly, the hugepage count remains stable, as configured by > the admin (me): > > HugePages_Total: 2048 > HugePages_Free: 2048 > HugePages_Rsvd: 0 > HugePages_Surp: 0 Thanks for giving it a spin David, that is highly appreciated ;-)! I will add above information in next's version changelog if you do not mind, so the before-and-after can be seen clearly. I shall send v4 in the course of the next few days. -- Oscar Salvador SUSE L3
