Re: [RFC][PATCH] radix-tree based page_cgroup. [6/7] radix-tree based page cgroup

[Hirokazu Takahashi <taka@valinux.co.jp>]

Hi,

> Hirokazu Takahashi <taka@valinux.co.jp> wrote:
> > The size of struct page_cgroup on 32bit will be 28byte,
> > so that sizeof(struct page_cgroup) * 2^8 = 28 * 2^8 = 7168 byte.
> > I'm not sure it is acceptable if we lose (8192 - 7168)/8192 = 0.125 = 12.5%
> > of memory for page_cgroup.
> > 
> > +struct page_cgroup {
> > +	struct page 		*page;       /* the page this accounts for*/
> > +	struct mem_cgroup 	*mem_cgroup; /* current cgroup subsys */
> > +	int    			flags;	     /* See below */
> > +	int    			refcnt;      /* reference count */
> > +	spinlock_t		lock;        /* lock for all above members */
> > +	struct list_head 	lru;         /* for per cgroup LRU */
> > +};
> > 
> 
> - 28bytes * (2^7) = 3584 bytes. wastes 608 bytes per 512k of user memory. 
> - 28bytes * (2^8) = 7168 bytes. wastes 1024 bytes per 1M of user memory.
> 
> loss is 0.1%. or any room user for page_cgroup's extra 4 bytes ?
> 
> Thanks,
> -Kame

I feel kernel memory is an expensive resource especially on 32 bit linux
machines. I think this is one of the reasones why a lot of people don't
want to increase the size of page structure.

Thank you,
Hirokazu Takahashi.

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