linux-kernel - Re: [PATCH RFC 2/2] net: Optimize snmp stat aggregation by walking all the percpu data at once

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Message-ID: <55DC9272.4050402@linux.vnet.ibm.com>
Date:	Tue, 25 Aug 2015 21:36:10 +0530
From:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	davem@...emloft.net, kuznet@....inr.ac.ru, jmorris@...ei.org,
	yoshfuji@...ux-ipv6.org, kaber@...sh.net, jiri@...nulli.us,
	edumazet@...gle.com, hannes@...essinduktion.org,
	tom@...bertland.com, azhou@...ira.com, ebiederm@...ssion.com,
	ipm@...rality.org.uk, nicolas.dichtel@...nd.com,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	anton@....ibm.com, nacc@...ux.vnet.ibm.com,
	srikar@...ux.vnet.ibm.com
Subject: Re: [PATCH RFC 2/2] net: Optimize snmp stat aggregation by walking
 all the percpu data at once

On 08/25/2015 09:30 PM, Eric Dumazet wrote:
> On Tue, 2015-08-25 at 21:17 +0530, Raghavendra K T wrote:
>> On 08/25/2015 07:58 PM, Eric Dumazet wrote:
>
>>>
>>>
>>> This is a great idea, but kcalloc()/kmalloc() can fail and you'll crash
>>> the whole kernel at this point.
>>>
>>
>> Good catch, and my bad. Though system is in bad memory condition,
>> since fill_stat is not critical for the system do you think silently
>> returning from here is a good idea?
>> or do you think we should handle with -ENOMEM way up.?
>
> Hmm... presumably these 288 bytes could be allocated in
> inet6_fill_ifla6_attrs() stack frame.
>
> Also it is weird we fill all these stats for a device we just created
> and never enabled : initial stats are all 0 for them.
>

Yes it is.. Initially I was even thinking

1. if we could disable the stat filling just after creation ( only
allocate the space for statistics but do not fill).

2. should we have a PROC_FS_NET_SNMP config which we can disable if not
necessary.

3. should we defer this snmp_fold_walk to a workqueue. (unfortunately
there is not much to do after this stat filling which can run in
parallel before we wait for completion.. or may be there is a way).





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