[Experimental] [PATCH 0/5] page_cgroup->flags diet.

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

For reducing size of page_cgroup, we need to reduce flags.

This patch is a trial to remove flags based on

linux-next + 
memcg-add-mem_cgroup_replace_page_cache-to-fix-lru-issue.patch +
4 patches for 'simplify LRU handling' I posted.

So, I don't ask anyone to test this but want to hear another idea
or comments on implemenation.

After this patch series, page_cgroup flags are 

enum {
        /* flags for mem_cgroup */
        PCG_LOCK,  /* Lock for pc->mem_cgroup and following bits. */
        PCG_USED, /* this object is in use. */
        PCG_MIGRATION, /* under page migration */
        __NR_PCG_FLAGS,
};

3bits. I thought I could remove PCG_MIGRATION ....but failed.

BTW, because of kmalloc()'s alignment, low 3bits of pc->mem_cgroup must be 0.
So, we can move these flags to low bits in pc->mem_cgroup...I guess.

(But in another thoughts, we need to track blkio per page finally. So, I'm
 not sure whether we can remove page_cgroup at the end.)

Anyway, I dump a current trial series. Please comment when you have time.
I'm not in hurry and will not be able to make a quick response.

Thanks,
-Kame


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