linux-kernel - Re: [PATCH] mm: memcontrol: only manage socket pressure for CONFIG

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Message-ID: <20151209185858.GA2342@cmpxchg.org>
Date:	Wed, 9 Dec 2015 13:58:58 -0500
From:	Johannes Weiner <hannes@...xchg.org>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	netdev@...r.kernel.org, cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: memcontrol: only manage socket pressure for
 CONFIG_INET

On Wed, Dec 09, 2015 at 05:32:16PM +0100, Arnd Bergmann wrote:
> When IPV4 support is disabled, the memcg->socket_pressure field is
> not defined and we get a build error from the vmpressure code:
> 
> mm/vmpressure.c: In function 'vmpressure':
> mm/vmpressure.c:287:9: error: 'struct mem_cgroup' has no member named 'socket_pressure'
>     memcg->socket_pressure = jiffies + HZ;
> mm/built-in.o: In function `mem_cgroup_css_free':
> :(.text+0x1c03a): undefined reference to `tcp_destroy_cgroup'
> mm/built-in.o: In function `mem_cgroup_css_online':
> :(.text+0x1c20e): undefined reference to `tcp_init_cgroup'
> 
> This puts the code causing this in the same #ifdef that guards the
> struct member and the TCP implementation.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> Fixes: 20cc40e66c42 ("mm: memcontrol: hook up vmpressure to socket pressure")

Acked-by: Johannes Weiner <hannes@...xchg.org>

> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 6faea81e66d7..73cd572167bb 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -4220,13 +4220,13 @@ mem_cgroup_css_online(struct cgroup_subsys_state *css)
>  	if (ret)
>  		return ret;
>  
> +#ifdef CONFIG_INET
>  #ifdef CONFIG_MEMCG_LEGACY_KMEM
>  	ret = tcp_init_cgroup(memcg);
>  	if (ret)
>  		return ret;
>  #endif

The calls to tcp_init_cgroup() appear earlier in the series than "mm:
memcontrol: hook up vmpressure to socket pressure". However, they get
moved around a few times so fixing it earlier means respinning the
series. Andrew, it's up to you whether we take the bisectability hit
for !CONFIG_INET && CONFIG_MEMCG (how common is this?) or whether you
want me to resend the series.

Sorry about the trouble. I don't have a git tree on kernel.org because
we don't really use git in -mm, but the downside is that we don't get
the benefits of the automatic build testing for all kinds of configs.
I'll try to set up a git tree to expose series to full build coverage
before they hit -mm and -next.
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