Re: [PATCH v7 4/4] mm: swap: filter swap allocation by memcg tier mask

[Nhat Pham]

On Sat, May 30, 2026 at 10:51 AM Nhat Pham <nphamcs@xxxxxxxxx> wrote:
>
>
> How expensive is it to add per-cpu caching for each device :(

to clarify - a percpu_swap_cluster per si for every si.

>

... or for each tier (assuming devices in each tier share the same
performance characteristics, and could be used interchangeably?).

Basically:

struct percpu_swap_cluster {
    struct swap_info_struct *si[MAX_SWAPTIER][SWAP_NR_ORDERS];
    unsigned long offset[MAX_SWAPTIER][SWAP_NR_ORDERS];
    local_lock_t lock;
};

Seems like 4 is the default number of tier right? So the extra
overhead is just (nr cpu) * 10 * 3 * (sizeof(unsigned long) +
sizeof(*ptr)) or wev?