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Subject: Re: [PATCH v3] mlx4_core: allocate ICM memory in page size chunks
To:     Qing Huang <qing.huang@oracle.com>, tariqt@mellanox.com,
        davem@davemloft.net, haakon.bugge@oracle.com, yanjun.zhu@oracle.com
Cc:     netdev@vger.kernel.org, linux-rdma@vger.kernel.org,
        linux-kernel@vger.kernel.org, gi-oh.kim@profitbricks.com
References: <20180517205343.8401-1-qing.huang@oracle.com>
From:   Eric Dumazet <eric.dumazet@gmail.com>
Message-ID: <e6c470f0-f2ae-5efd-09ed-0c9562a4a764@gmail.com>
Date:   Thu, 17 May 2018 14:14:20 -0700
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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 at https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=d8c13f2271ec5178c52fbde072ec7b562651ed9d

And you'll understand some people care about this.

Strongly.

Thanks.