netdev - Re: [PATCH] prevent the read ahead of /proc/slabinfo in ss take 2

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Message-ID: <54D9FB96.6080401@cogentembedded.com>
Date:	Tue, 10 Feb 2015 15:37:42 +0300
From:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:	Bryton Lee <brytonlee01@...il.com>, stephen@...workplumber.org,
	netdev@...r.kernel.org, davem@...emloft.net
CC:	eric.dumazet@...il.com
Subject: Re: [PATCH] prevent the read ahead of /proc/slabinfo in ss take 2

Hello.

On 2/10/2015 5:46 AM, Bryton Lee wrote:

> ss reads ahead of /proc/slabinfo whatever slabstat will be used or not in future.
> this will cause huge system delay when the kernel hires SLAB allocator(SLUB allocator is ok). when program reads
> /proc/slabinfo, it will call s_show() in SLAB allocator level, and s_show() calls spin_lock_irq(&l3->list_lock)
> then iterate on whole three lists. if one slab has about 900 million objects (for example dentry),
> it will cause more than 1000ms delay.

> so this patch prevents the read ahead of /proc/slabinfo, ss runs with most parameters not using slabstat at all.
> and this patch also change slabstat and slabstat_valid to static.

> Signed-off-by: Bryton Lee <brytonlee01@...il.com>
> ---
>   misc/ss.c | 11 ++++++++---
>   1 file changed, 8 insertions(+), 3 deletions(-)

> diff --git a/misc/ss.c b/misc/ss.c
> index 7fc0a99..5fa6259 100644
> --- a/misc/ss.c
> +++ b/misc/ss.c
> @@ -616,7 +616,8 @@ struct slabstat
>   	int skbs;
>   };
>
> -struct slabstat slabstat;
> +static struct slabstat slabstat;
> +static int slabstat_valid = 0;

    No need to initialize to 0.

[...]

WBR, Sergei

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