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

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Date:   Wed, 30 May 2018 16:50:22 -0400
From:   Eric Dumazet <edumazet@...gle.com>
To:     Qing Huang <qing.huang@...cle.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>
Subject: Re: [PATCH net] mlx4_core: restore optimal ICM memory allocation

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.

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 !)

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 )