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

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Message-ID: <19b7818e-16f6-2349-dc34-245c2f215f6f@oracle.com>
Date:   Thu, 17 May 2018 14:45:20 -0700
From:   Qing Huang <qing.huang@...cle.com>
To:     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 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.

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