Snap installed lxd can not map memory limits

Hi, I’m using Centos 7 and snap.
After installed lxd 5.15, I tried to create a container with limits.memory 512M, but when I exec bin bash inside it,
I saw the free is 2G, and the bytes in memory cgroup mount file shows a huge number.

I don’t know how to fix that problem, I think snap already have a how can I solve this problem? Thanks