Re: [PATCH v3 0/2] Make alloc_contig_range handle Hugetlb pages

Oscar Salvador
2021-03-01T12:59:05Z

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