On 01.03.21 13:57, Oscar Salvador wrote:
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.
I'll have some review feedback on error handling that might be improved,
I'll share that shortly.
--
Thanks,
David / dhildenb
