Balbir Singh wrote:
> 
> -------- Original Message --------
> Subject: [PATCH -RSS 2/2] Fix limit check after reclaim
> Date: Mon, 04 Jun 2007 21:03:04 +0530
> From: Balbir Singh <balbir@linux.vnet.ibm.com>
> To: Andrew Morton <akpm@osdl.org>
> CC: Linux Containers <containers@lists.osdl.org>,        Balbir Singh <balbir@linux.vnet.ibm.com>,        Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>,        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
> References: <20070604153244.31748.50043.sendpatchset@balbir-laptop>
> 
> 
> 
> This patch modifies the reclaim behaviour such that before calling the
> container out of memory routine, it checks if as a result of the reclaim
> (even though pages might not be fully reclaimed), the resident set size
> of the container decreased before declaring the container as out of memory
> 
> Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com>
> ---
> 
>  include/linux/res_counter.h |   23 +++++++++++++++++++++++
>  mm/rss_container.c          |   11 +++++++++++
>  2 files changed, 34 insertions(+)
> 
> diff -puN mm/rss_container.c~rss-fix-limit-check-after-reclaim mm/rss_container.c
> --- linux-2.6.22-rc2-mm1/mm/rss_container.c~rss-fix-limit-check-after-reclaim	2007-06-04 20:13:40.000000000 +0530
> +++ linux-2.6.22-rc2-mm1-balbir/mm/rss_container.c	2007-06-04 20:13:40.000000000 +0530
> @@ -114,6 +114,17 @@ int container_rss_prepare(struct page *p
>  			continue;
>  		}
> 
> +		/*
> + 		 * try_to_free_pages() might not give us a full picture
> + 		 * of reclaim. Some pages are reclaimed and might be moved
> + 		 * to swap cache or just unmapped from the container.
> + 		 * Check the limit again to see if the reclaim reduced the
> + 		 * current usage of the container before calling the
> + 		 * container OOM routine
> + 		 */
> +		if (res_counter_check_under_limit(&rss->res))
> +			continue;
> +
>  		container_out_of_memory(rss);
>  		if (test_thread_flag(TIF_MEMDIE))
>  			goto out_charge;
> diff -puN include/linux/res_counter.h~rss-fix-limit-check-after-reclaim include/linux/res_counter.h
> --- linux-2.6.22-rc2-mm1/include/linux/res_counter.h~rss-fix-limit-check-after-reclaim	2007-06-04 20:13:40.000000000 +0530
> +++ linux-2.6.22-rc2-mm1-balbir/include/linux/res_counter.h	2007-06-04 20:15:46.000000000 +0530
> @@ -99,4 +99,27 @@ int res_counter_charge(struct res_counte
>  void res_counter_uncharge_locked(struct res_counter *cnt, unsigned long val);
>  void res_counter_uncharge(struct res_counter *cnt, unsigned long val);
> 
> +static inline bool res_counter_limit_check_locked(struct res_counter *cnt)
> +{
> +	if (cnt->usage < cnt->limit)
> +		return true;
> +
> +	return false;
> +}
> +
> +/*
> + * Helper function to detect if the container is within it's limit or
> + * not. It's currently called from container_rss_prepare()
> + */
> +static inline bool res_counter_check_under_limit(struct res_counter *cnt)
> +{
> +	bool ret;
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&cnt->lock, flags);
> +	ret = res_counter_limit_check_locked(cnt);

We don't have to take the lock for such a check.

> +	spin_unlock_irqrestore(&cnt->lock, flags);
> +	return ret;
> +}
> +
>  #endif
> diff -puN mm/vmscan.c~rss-fix-limit-check-after-reclaim mm/vmscan.c
> _
> 

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Balbir Singh wrote:
> Pavel Emelianov wrote:
>>> +static inline bool res_counter_check_under_limit(struct res_counter *cnt)
>>> +{
>>> +	bool ret;
>>> +	unsigned long flags;
>>> +
>>> +	spin_lock_irqsave(&cnt->lock, flags);
>>> +	ret = res_counter_limit_check_locked(cnt);
>> We don't have to take the lock for such a check.
>>
>  
> This check without the lock could be racy and return incorrect
> results -- leading to OOM.

Maybe. Nevertheless, if we do not trust the return value of
try_to_free_pages() then the code should probably look like

while (1) {
	if (res_counter_charge() == 0)
		break;

	did_progress = try_to_free_pages();
	if (res_counter_charge() == 0)
		break;

	if (!did_progress)
		out_of_memory();
}

But in any case we must know for sure was at least one page
freed or not...

Thanks,
Pavel
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Pavel Emelianov wrote:
>> +static inline bool res_counter_check_under_limit(struct res_counter *cnt)
>> +{
>> +	bool ret;
>> +	unsigned long flags;
>> +
>> +	spin_lock_irqsave(&cnt->lock, flags);
>> +	ret = res_counter_limit_check_locked(cnt);
> 
> We don't have to take the lock for such a check.
> 
 
This check without the lock could be racy and return incorrect
results -- leading to OOM.


-- 
	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL
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Pavel Emelianov wrote:
> Balbir Singh wrote:
>> Pavel Emelianov wrote:
>>>> +static inline bool res_counter_check_under_limit(struct res_counter *cnt)
>>>> +{
>>>> +	bool ret;
>>>> +	unsigned long flags;
>>>> +
>>>> +	spin_lock_irqsave(&cnt->lock, flags);
>>>> +	ret = res_counter_limit_check_locked(cnt);
>>> We don't have to take the lock for such a check.
>>>
>>  
>> This check without the lock could be racy and return incorrect
>> results -- leading to OOM.
> 
> Maybe. Nevertheless, if we do not trust the return value of
> try_to_free_pages() then the code should probably look like
> 
> while (1) {
> 	if (res_counter_charge() == 0)
> 		break;
> 
> 	did_progress = try_to_free_pages();
> 	if (res_counter_charge() == 0)
> 		break;
> 
> 	if (!did_progress)
> 		out_of_memory();
> }
> 

Yes, this looks better.

> But in any case we must know for sure was at least one page
> freed or not...
> 
> Thanks,
> Pavel


-- 
	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL
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