linux-kernel - Re: [RFC][PATCH 02/11] blkiocg async: The main part of iotrack

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Date:	Wed, 14 Jul 2010 10:46:31 -0400
From:	Munehiro IKEDA <m-ikeda@...jp.nec.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
CC:	linux-kernel@...r.kernel.org, Vivek Goyal <vgoyal@...hat.com>,
	Ryo Tsuruta <ryov@...inux.co.jp>, taka@...inux.co.jp,
	Andrea Righi <righi.andrea@...il.com>,
	Gui Jianfeng <guijianfeng@...fujitsu.com>,
	akpm@...ux-foundation.org, balbir@...ux.vnet.ibm.com
Subject: Re: [RFC][PATCH 02/11] blkiocg async: The main part of iotrack

KAMEZAWA Hiroyuki wrote: 
> On Fri, 09 Jul 2010 19:06:28 -0400
> Munehiro Ikeda <m-ikeda@...jp.nec.com> wrote:
> 
>> OK, we can do it like:
>>
>> do {
>> 	old =  pc->flags;
>> 	new = old & ((1UL << PAGE_TRACKING_ID_SHIFT) - 1);
>> 	new |= (unsigned long)(id << PAGE_TRACKING_ID_SHIFT);
>> } while (cmpxchg(&pc->flags, old, new)  != old);
>>
>>
>>> IIUC, there is an generic version now even if it's heavy.
>> I couldn't find it out...is there already?  Or you mean we should
>> have generic one?
>>
> 
> generic cmpxchg in /include/asm-generic/cmpxchg.h
> But...ahh...in some arch, you can't use cmpxchg, sorry.
> 
> How about start from "a new field" for I/O cgroup in page_cgroup ?
> 
> struct page_cgroup {
>         unsigned long flags;
>         struct mem_cgroup *mem_cgroup;
> 	unsigned short blkio_cgroup_id;
>         struct page *page;
>         struct list_head lru;           /* per cgroup LRU list */
> };
> 
> We can consider how we optimize it out, later.
> (And, it's easier to debug and make development smooth.)
> 
> For example, If we can create a vmalloced-array of mem_cgroup,
> id->mem_cgroup lookup can be very fast and we can replace
> pc->mem_cgroup link with pc->mem_cgroup_id.

Nice suggestion.  Thanks Kame-san.


>>>> +unsigned long page_cgroup_get_owner(struct page *page);
>>>> +int page_cgroup_set_owner(struct page *page, unsigned long id);
>>>> +int page_cgroup_copy_owner(struct page *npage, struct page *opage);
>>>> +
>>>>   void __meminit pgdat_page_cgroup_init(struct pglist_data *pgdat);
>>>>
>>>>   #ifdef CONFIG_SPARSEMEM
>>>> diff --git a/init/Kconfig b/init/Kconfig
>>>> index 2e40f2f..337ee01 100644
>>>> --- a/init/Kconfig
>>>> +++ b/init/Kconfig
>>>> @@ -650,7 +650,7 @@ endif # CGROUPS
>>>>
>>>>   config CGROUP_PAGE
>>>>   	def_bool y
>>>> -	depends on CGROUP_MEM_RES_CTLR
>>>> +	depends on CGROUP_MEM_RES_CTLR || GROUP_IOSCHED_ASYNC
>>>>
>>>>   config MM_OWNER
>>>>   	bool
>>>> diff --git a/mm/page_cgroup.c b/mm/page_cgroup.c
>>>> index 6c00814..69e080c 100644
>>>> --- a/mm/page_cgroup.c
>>>> +++ b/mm/page_cgroup.c
>>>> @@ -9,6 +9,7 @@
>>>>   #include<linux/vmalloc.h>
>>>>   #include<linux/cgroup.h>
>>>>   #include<linux/swapops.h>
>>>> +#include<linux/blk-iotrack.h>
>>>>
>>>>   static void __meminit
>>>>   __init_page_cgroup(struct page_cgroup *pc, unsigned long pfn)
>>>> @@ -74,7 +75,7 @@ void __init page_cgroup_init_flatmem(void)
>>>>
>>>>   	int nid, fail;
>>>>
>>>> -	if (mem_cgroup_disabled())
>>>> +	if (mem_cgroup_disabled()&&  blk_iotrack_disabled())
>>>>   		return;
>>>>
>>>>   	for_each_online_node(nid)  {
>>>> @@ -83,12 +84,13 @@ void __init page_cgroup_init_flatmem(void)
>>>>   			goto fail;
>>>>   	}
>>>>   	printk(KERN_INFO "allocated %ld bytes of page_cgroup\n", total_usage);
>>>> -	printk(KERN_INFO "please try 'cgroup_disable=memory' option if you"
>>>> -	" don't want memory cgroups\n");
>>>> +	printk(KERN_INFO "please try 'cgroup_disable=memory,blkio' option"
>>>> +	" if you don't want memory and blkio cgroups\n");
>>>>   	return;
>>>>   fail:
>>>>   	printk(KERN_CRIT "allocation of page_cgroup failed.\n");
>>>> -	printk(KERN_CRIT "please try 'cgroup_disable=memory' boot option\n");
>>>> +	printk(KERN_CRIT
>>>> +		"please try 'cgroup_disable=memory,blkio' boot option\n");
>>>>   	panic("Out of memory");
>>>>   }
>>> Hmm, io-track is always done if blkio-cgroup is used, Right ?
>> No, iotrack is enabled only when CONFIG_GROUP_IOSCHED_ASYNC=y.
>> If =n, iotrack is disabled even if blkio-cgroup is enabled.
>>
> 
> 
>>> Then, why you have extra config as CONFIG_GROUP_IOSCHED_ASYNC ?
>>> Is it necessary ?
>> Current purpose of the option is only for debug because it is
>> experimental functionality.
>> It can be removed if this work is completed, or dynamic switch
>> might be useful.
>>
>> In fact, just "cgroup_disable=memory" is enough for the failure
>> case.  Let me think right messages.
>>
> 
> IMHO, once you add boot-option or sysctl, it's very hard to remove it, lator.
> So, if you think you'll remove it lator, don't add it or just add CONFIG.

OK.  I understand we need to seriously think over to add a new boot option.


Thanks,
Muuhh


-- 
IKEDA, Munehiro
  NEC Corporation of America
    m-ikeda@...jp.nec.com

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