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SubjectRe: [PATCH] use CSS ID in swap_cgroup for saving memory
>  static inline
> -struct mem_cgroup *swap_cgroup_record(swp_entry_t ent, struct mem_cgroup *mem)
> +unsigned short swap_cgroup_record(swp_entry_t ent, unsigned short id)
> {
> return NULL;

return 0;

> }
>
> static inline
> -struct mem_cgroup *lookup_swap_cgroup(swp_entry_t ent)
> +unsigned short lookup_swap_cgroup(swp_entry_t ent)
> {
> return NULL;

return 0;

> }

> @@ -1265,12 +1286,20 @@ int mem_cgroup_cache_charge(struct page
>
> if (do_swap_account && !ret && PageSwapCache(page)) {
> swp_entry_t ent = {.val = page_private(page)};
> + unsigned short id;
> /* avoid double counting */
> - mem = swap_cgroup_record(ent, NULL);
> + id = swap_cgroup_record(ent, 0);
> + rcu_read_lock();
> + mem = mem_cgroup_lookup(id);
> if (mem) {
> + /*
> + * Recorded ID can be obsolete. We avoid calling
> + * css_tryget()
> + */
> res_counter_uncharge(&mem->memsw, PAGE_SIZE);
> mem_cgroup_put(mem);
> }
> + rcu_read_unlock();
> }
> return ret;
> }
> @@ -1335,13 +1364,21 @@ void mem_cgroup_commit_charge_swapin(str
> */
> if (do_swap_account && PageSwapCache(page)) {
> swp_entry_t ent = {.val = page_private(page)};
> + unsigned short id;
> struct mem_cgroup *memcg;
> - memcg = swap_cgroup_record(ent, NULL);
> +
> + id = swap_cgroup_record(ent, 0);
> + rcu_read_lock();
> + memcg = mem_cgroup_lookup(id);
> if (memcg) {
> + /*
> + * This recorded memcg can be obsolete one. So, avoid
> + * calling css_tryget
> + */
> res_counter_uncharge(&memcg->memsw, PAGE_SIZE);
> mem_cgroup_put(memcg);
> }
> -
> + rcu_read_unlock();
> }
> /* add this page(page_cgroup) to the LRU we want. */
>
> @@ -1462,7 +1499,7 @@ void mem_cgroup_uncharge_swapcache(struc
> MEM_CGROUP_CHARGE_TYPE_SWAPOUT);
> /* record memcg information */
> if (do_swap_account && memcg) {
> - swap_cgroup_record(ent, memcg);
> + swap_cgroup_record(ent, css_id(&memcg->css));
> mem_cgroup_get(memcg);
> }
> if (memcg)
> @@ -1477,15 +1514,22 @@ void mem_cgroup_uncharge_swapcache(struc
> void mem_cgroup_uncharge_swap(swp_entry_t ent)
> {
> struct mem_cgroup *memcg;
> + unsigned short id;
>
> if (!do_swap_account)
> return;
>
> - memcg = swap_cgroup_record(ent, NULL);
> + id = swap_cgroup_record(ent, 0);
> + rcu_read_lock();
> + memcg = mem_cgroup_lookup(id);
> if (memcg) {
> + /*
> + * This memcg can be obsolete one. We avoid calling css_tryget
> + */
> res_counter_uncharge(&memcg->memsw, PAGE_SIZE);
> mem_cgroup_put(memcg);
> }
> + rcu_read_unlock();

can we have a common function for the above 3 pieces of code?

> }
> #endif
>
> Index: mmotm-2.6.29-Feb24/mm/page_cgroup.c
> ===================================================================
> --- mmotm-2.6.29-Feb24.orig/mm/page_cgroup.c
> +++ mmotm-2.6.29-Feb24/mm/page_cgroup.c
> @@ -290,7 +290,7 @@ struct swap_cgroup_ctrl swap_cgroup_ctrl
> * cgroup rather than pointer.
> */

this comment should be updated/removed:

/*
* This 8bytes seems big..maybe we can reduce this when we can use "id" for
* cgroup rather than pointer.
*/

> struct swap_cgroup {
> - struct mem_cgroup *val;
> + unsigned short id;
> };
> #define SC_PER_PAGE (PAGE_SIZE/sizeof(struct swap_cgroup))
> #define SC_POS_MASK (SC_PER_PAGE - 1)


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