netdev - Re: [PATCH net] mlx4_core: restore optimal ICM memory allocation

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Date:   Wed, 30 May 2018 14:08:47 -0700
From:   Qing Huang <qing.huang@...cle.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     David Miller <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        John Sperbeck <jsperbeck@...gle.com>,
        Tarick Bedeir <tarick@...gle.com>,
        Daniel Jurgens <danielj@...lanox.com>,
        Zhu Yanjun <yanjun.zhu@...cle.com>,
        Tariq Toukan <tariqt@...lanox.com>, linux-rdma@...r.kernel.org,
        "santosh.shilimkar@...cle.com" <santosh.shilimkar@...cle.com>
Subject: Re: [PATCH net] mlx4_core: restore optimal ICM memory allocation



On 5/30/2018 1:50 PM, Eric Dumazet wrote:
> On Wed, May 30, 2018 at 4:30 PM Qing Huang <qing.huang@...cle.com> wrote:
>>
>>
>> On 5/29/2018 9:11 PM, Eric Dumazet wrote:
>>> Commit 1383cb8103bb ("mlx4_core: allocate ICM memory in page size chunks")
>>> brought a regression caught in our regression suite, thanks to KASAN.
>> If KASAN reported issue was really caused by smaller chunk sizes,
>> changing allocation
>> order dynamically will eventually hit the same issue.
> Sigh, you have little idea of what your patch really did...
>
> The KASAN part only shows the tip of the iceberg, but our main concern
> is an increase of memory overhead.

Well, the commit log only mentioned KASAN and but the change here didn't 
seem to solve
the issue.

>
> Alternative is to revert your patch, since we are now very late in 4.17 cycle.
>
> Memory usage has grown a lot with your patch, since each 4KB page needs a full
> struct mlx4_icm_chunk (256 bytes of overhead !)

Going to smaller chunks will have some overhead. It depends on the 
application though.
What's the total increased memory consumption in your env?

>
> Really we have no choice here, your patch went too far and increased
> memory consumption quite a lot.



>
> My patch is simply the best way to address your original concern, and
> not increase overall overhead.
>
> ( each struct mlx4_icm_chunk should be able to store
> MLX4_ICM_CHUNK_LEN pages, instead of one page of 4KB )