linux-kernel - Re: [PATCH v3] mlx4_core: allocate ICM memory in page size chunks

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Message-ID: <35ba0f14-7b24-96ff-6b2d-610a4b2980c2@mellanox.com>
Date:   Tue, 22 May 2018 18:33:21 +0300
From:   Tariq Toukan <tariqt@...lanox.com>
To:     Qing Huang <qing.huang@...cle.com>,
        Eric Dumazet <eric.dumazet@...il.com>, tariqt@...lanox.com,
        davem@...emloft.net, haakon.bugge@...cle.com, yanjun.zhu@...cle.com
Cc:     netdev@...r.kernel.org, linux-rdma@...r.kernel.org,
        linux-kernel@...r.kernel.org, gi-oh.kim@...fitbricks.com
Subject: Re: [PATCH v3] mlx4_core: allocate ICM memory in page size chunks



On 18/05/2018 12:45 AM, Qing Huang wrote:
> 
> 
> On 5/17/2018 2:14 PM, Eric Dumazet wrote:
>> On 05/17/2018 01:53 PM, Qing Huang wrote:
>>> When a system is under memory presure (high usage with fragments),
>>> the original 256KB ICM chunk allocations will likely trigger kernel
>>> memory management to enter slow path doing memory compact/migration
>>> ops in order to complete high order memory allocations.
>>>
>>> When that happens, user processes calling uverb APIs may get stuck
>>> for more than 120s easily even though there are a lot of free pages
>>> in smaller chunks available in the system.
>>>
>>> Syslog:
>>> ...
>>> Dec 10 09:04:51 slcc03db02 kernel: [397078.572732] INFO: task
>>> oracle_205573_e:205573 blocked for more than 120 seconds.
>>> ...
>>>
>> NACK on this patch.
>>
>> You have been asked repeatedly to use kvmalloc()
>>
>> This is not a minor suggestion.
>>
>> Take a look 
>> athttps://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=d8c13f2271ec5178c52fbde072ec7b562651ed9d 
>>
> 
> Would you please take a look at how table->icm is being used in the mlx4 
> driver? It's a meta data used for individual pointer variable referencing,
> not as data frag or in/out buffer. It has no need for contiguous phy. 
> memory.
> 
> Thanks.
> 

NACK.

This would cause a degradation when iterating the entries of table->icm.
For example, in mlx4_table_get_range.

Thanks,
Tariq

>> And you'll understand some people care about this.
>>
>> Strongly.
>>
>> Thanks.
>>
>