[Devel] Re: [PATCH 2/4] swapcgroup: add member to swap_info_struct for cgroup

[Daisuke Nishimura]

Hi.

On 2008/05/22 16:23 +0900, KAMEZAWA Hiroyuki wrote:
> On Thu, 22 May 2008 15:18:51 +0900
> Daisuke Nishimura <nishimura at mxp.nes.nec.co.jp> wrote:
> 
>> This patch add a member to swap_info_struct for cgroup.
>>
>> This member, array of pointers to mem_cgroup, is used to
>> remember to which cgroup each swap entries are charged.
>>
>> The memory for this array of pointers is allocated on swapon,
>> and freed on swapoff.
>>
> Hi, in general, #ifdefs in the middle of functions are not good style.
> I'd like to comment some hints.
> 
I completely agree that it's not good style.

>> Signed-off-by: Daisuke Nishimura <nishimura at mxp.nes.nec.co.jp>
>>
>> ---
>>  include/linux/swap.h |    3 +++
>>  mm/swapfile.c        |   32 ++++++++++++++++++++++++++++++++
>>  2 files changed, 35 insertions(+), 0 deletions(-)
>>
>> diff --git a/include/linux/swap.h b/include/linux/swap.h
>> index de40f16..67de27b 100644
>> --- a/include/linux/swap.h
>> +++ b/include/linux/swap.h
>> @@ -141,6 +141,9 @@ struct swap_info_struct {
>>  	struct swap_extent *curr_swap_extent;
>>  	unsigned old_block_size;
>>  	unsigned short * swap_map;
>> +#ifdef CONFIG_CGROUP_SWAP_RES_CTLR
>> +	struct mem_cgroup **memcg;
>> +#endif
>>  	unsigned int lowest_bit;
>>  	unsigned int highest_bit;
>>  	unsigned int cluster_next;
>> diff --git a/mm/swapfile.c b/mm/swapfile.c
>> index d3caf3a..232bf20 100644
>> --- a/mm/swapfile.c
>> +++ b/mm/swapfile.c
>> @@ -1207,6 +1207,9 @@ asmlinkage long sys_swapoff(const char __user * specialfile)
>>  {
>>  	struct swap_info_struct * p = NULL;
>>  	unsigned short *swap_map;
>> +#ifdef CONFIG_CGROUP_SWAP_RES_CTLR
>> +	struct mem_cgroup **memcg;
>> +#endif
> Remove #ifdef.
> 
>  struct mem_cgroup **memcg = NULL;
> 
good idea.
I'll do it.

>>  	struct file *swap_file, *victim;
>>  	struct address_space *mapping;
>>  	struct inode *inode;
>> @@ -1309,10 +1312,17 @@ asmlinkage long sys_swapoff(const char __user * specialfile)
>>  	p->max = 0;
>>  	swap_map = p->swap_map;
>>  	p->swap_map = NULL;
>> +#ifdef CONFIG_CGROUP_SWAP_RES_CTLR
>> +	memcg = p->memcg;
>> +	p->memcg = NULL;
>> +#endif
> 
> 
> ==
> #ifdef CONFIG_CGROUP_SWAP_RES_CTR
>   void  swap_cgroup_init_memcg(p, memcg)
>   {
>     do something.
>   }
> #else
>    void  swap_cgroup_init_memcg(p, memcg)
>   {
>   }
> #endif
> ==
> 
I think swap_cgroup_init_memcg should return old value
of p->memcg, and I would like to name it swap_cgroup_clear_memcg,
because it is called by sys_swapoff, so "clear" rather than "init"
would be better.

How about something like this?

struct mem_cgroup **swap_cgroup_clear_memcg(p, memcg)
{
	struct mem_cgroup **mem;

	mem = p->memcg;
	p->memcg = NULL;

	return mem;
}

and at sys_swapoff():

struct mem_cgroup **memcg;
 :
memcg = swap_cgroup_clear_memcg(p, memcg);
 :
if (memcg)
	vfree(memcg);

>>  	p->flags = 0;
>>  	spin_unlock(&swap_lock);
>>  	mutex_unlock(&swapon_mutex);
>>  	vfree(swap_map);
>> +#ifdef CONFIG_CGROUP_SWAP_RES_CTLR
>> +	vfree(memcg);
>> +#endif
>  if (memcg)
>       vfree(memcg);
> 
> 
will do.

>>  	inode = mapping->host;
>>  	if (S_ISBLK(inode->i_mode)) {
>>  		struct block_device *bdev = I_BDEV(inode);
>> @@ -1456,6 +1466,9 @@ asmlinkage long sys_swapon(const char __user * specialfile, int swap_flags)
>>  	unsigned long maxpages = 1;
>>  	int swapfilesize;
>>  	unsigned short *swap_map;
>> +#ifdef CONFIG_CGROUP_SWAP_RES_CTLR
>> +	struct mem_cgroup **memcg;
>> +#endif
> Remove #ifdefs
> 
will do.

>>  	struct page *page = NULL;
>>  	struct inode *inode = NULL;
>>  	int did_down = 0;
>> @@ -1479,6 +1492,9 @@ asmlinkage long sys_swapon(const char __user * specialfile, int swap_flags)
>>  	p->swap_file = NULL;
>>  	p->old_block_size = 0;
>>  	p->swap_map = NULL;
>> +#ifdef CONFIG_CGROUP_SWAP_RES_CTLR
>> +	p->memcg = NULL;
>> +#endif
> 
> void init_swap_ctlr_memcg(p);
> 
I would like to call this one swap_cgroup_init_memcg.

>>  	p->lowest_bit = 0;
>>  	p->highest_bit = 0;
>>  	p->cluster_nr = 0;
>> @@ -1651,6 +1667,15 @@ asmlinkage long sys_swapon(const char __user * specialfile, int swap_flags)
>>  				1 /* header page */;
>>  		if (error)
>>  			goto bad_swap;
>> +
>> +#ifdef CONFIG_CGROUP_SWAP_RES_CTLR
>> +		p->memcg = vmalloc(maxpages * sizeof(struct mem_cgroup *));
>> +		if (!p->memcg) {
>> +			error = -ENOMEM;
>> +			goto bad_swap;
>> +		}
>> +		memset(p->memcg, 0, maxpages * sizeof(struct mem_cgroup *));
>> +#endif
> void alloc_swap_ctlr_memcg(p)
> 
OK.
I'll implement swap_cgroup_alloc_memcg.

> But this implies swapon will fail at memory shortage. Is it good ?
> 
Hum.
Would it be better to just disabling this feature?

>>  	}
>>  
>>  	if (nr_good_pages) {
>> @@ -1710,11 +1735,18 @@ bad_swap_2:
>>  	swap_map = p->swap_map;
>>  	p->swap_file = NULL;
>>  	p->swap_map = NULL;
>> +#ifdef CONFIG_CGROUP_SWAP_RES_CTLR
>> +	memcg = p->memcg;
>> +	p->memcg = NULL;
>> +#endif
>>  	p->flags = 0;
>>  	if (!(swap_flags & SWAP_FLAG_PREFER))
>>  		++least_priority;
>>  	spin_unlock(&swap_lock);
>>  	vfree(swap_map);
>> +#ifdef CONFIG_CGROUP_SWAP_RES_CTLR
>> +	vfree(memcg);
>> +#endif
>>  	if (swap_file)
>>  		filp_close(swap_file, NULL);
>>  out:
>>
I'll handle these 2 #ifdefs as sys_swapoff.

>>
> 
> Thanks,
> -Kame
> 

Thank you for your advice!


Daisuke Nishimura.
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