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

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Date:   Wed, 30 May 2018 17:30:18 -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>,
        linux-rdma <linux-rdma@...r.kernel.org>,
        Santosh Shilimkar <santosh.shilimkar@...cle.com>
Subject: Re: [PATCH net] mlx4_core: restore optimal ICM memory allocation

On Wed, May 30, 2018 at 5:08 PM Qing Huang <qing.huang@...cle.com> wrote:
>
>
>
> 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.

Can you elaborate ?

My patch solves our problems.

Both the memory overhead and KASAN splats are gone.

>
> >
> > 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?


As I explained, your patch adds 256 bytes of overhead per 4KB.

Your changelog did not mentioned that at all, and we discovered this
the hard way.

That is pretty intolerable, and is a blocker for us, memory is precious.