On 17.02.21 14:59, Michal Hocko wrote:
On Wed 17-02-21 14:53:37, David Hildenbrand wrote:
On 17.02.21 14:50, Michal Hocko wrote:
[...]
Do we have any real life examples? Or does this fall more into, let's
optimize an existing implementation category.
It's a big TODO item I have on my list and I am happy that Oscar is looking
into it. So yes, I noticed it while working on virtio-mem. It's real.
Do not take me wrong, I am not opposing to the functionality. I am
asking for the specific usecase.
Makes sense, and a proper motivation should be included in the
patches/cover letter. So here comes a quick-n-dirty example:
Start a VM with 4G. Hotplug 1G via virtio-mem and online it to
ZONE_MOVABLE. Allocate 512 huge pages.
[root@localhost ~]# cat /proc/meminfo
MemTotal: 5061512 kB
MemFree: 3319396 kB
MemAvailable: 3457144 kB
...
HugePages_Total: 512
HugePages_Free: 512
HugePages_Rsvd: 0
HugePages_Surp: 0
Hugepagesize: 2048 kB
The huge pages get partially allocate from ZONE_MOVABLE. Try unplugging
1G via virtio-mem (remember, all ZONE_MOVABLE). Inside the guest:
[ 180.058992] alloc_contig_range: [1b8000, 1c0000) PFNs busy
[ 180.060531] alloc_contig_range: [1b8000, 1c0000) PFNs busy
[ 180.061972] alloc_contig_range: [1b8000, 1c0000) PFNs busy
[ 180.063413] alloc_contig_range: [1b8000, 1c0000) PFNs busy
[ 180.064838] alloc_contig_range: [1b8000, 1c0000) PFNs busy
[ 180.065848] alloc_contig_range: [1bfc00, 1c0000) PFNs busy
[ 180.066794] alloc_contig_range: [1bfc00, 1c0000) PFNs busy
[ 180.067738] alloc_contig_range: [1bfc00, 1c0000) PFNs busy
[ 180.068669] alloc_contig_range: [1bfc00, 1c0000) PFNs busy
[ 180.069598] alloc_contig_range: [1bfc00, 1c0000) PFNs busy
I succeed in unplugging 540MB - 484 MB remain blocked by huge pages
("which did not end up there by pure luck"). These pages are movable
(and even free!) and can easily be reallocated.
--
Thanks,
David / dhildenb
