netdev - Re: [PATCH net-next 0/2] net/sctp: Avoid allocating high order memory with kmalloc()

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Message-ID: <20180423213314.GG3711@localhost.localdomain>
Date:   Mon, 23 Apr 2018 18:33:15 -0300
From:   Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
To:     Oleg Babin <obabin@...tuozzo.com>
Cc:     netdev@...r.kernel.org, linux-sctp@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        Vlad Yasevich <vyasevich@...il.com>,
        Neil Horman <nhorman@...driver.com>,
        Xin Long <lucien.xin@...il.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>
Subject: Re: [PATCH net-next 0/2] net/sctp: Avoid allocating high order
 memory with kmalloc()

Hi,

On Mon, Apr 23, 2018 at 09:41:04PM +0300, Oleg Babin wrote:
> Each SCTP association can have up to 65535 input and output streams.
> For each stream type an array of sctp_stream_in or sctp_stream_out
> structures is allocated using kmalloc_array() function. This function
> allocates physically contiguous memory regions, so this can lead
> to allocation of memory regions of very high order, i.e.:
>
>   sizeof(struct sctp_stream_out) == 24,
>   ((65535 * 24) / 4096) == 383 memory pages (4096 byte per page),
>   which means 9th memory order.
>
> This can lead to a memory allocation failures on the systems
> under a memory stress.

Did you do performance tests while actually using these 65k streams
and with 256 (so it gets 2 pages)?

This will introduce another deref on each access to an element, but
I'm not expecting any impact due to it.

  Marcelo