mnt_pcp
struct mnt_pcp __percpu *mnt_pcp;
this_cpu_add(mnt->mnt_pcp->mnt_count, n);
count += per_cpu_ptr(mnt->mnt_pcp, cpu)->mnt_count;
mnt->mnt_pcp = alloc_percpu(struct mnt_pcp);
if (!mnt->mnt_pcp)
this_cpu_add(mnt->mnt_pcp->mnt_count, 1);
this_cpu_inc(mnt->mnt_pcp->mnt_writers);
this_cpu_dec(mnt->mnt_pcp->mnt_writers);
count += per_cpu_ptr(mnt->mnt_pcp, cpu)->mnt_writers;
free_percpu(mnt->mnt_pcp);