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

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Message-Id: <20151209151326.f7efba4e5697e1b0f212ea34@linux-foundation.org>
Date:	Wed, 9 Dec 2015 15:13:26 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	Arnd Bergmann <arnd@...db.de>, 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, 9 Dec 2015 18:05:05 -0500 Johannes Weiner <hannes@...xchg.org> wrote:

> On Wed, Dec 09, 2015 at 02:28:36PM -0800, Andrew Morton wrote:
> > On Wed, 9 Dec 2015 13:58:58 -0500 Johannes Weiner <hannes@...xchg.org> wrote:
> > > 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.
> > 
> > hm, drat, I was suspecting dependency issues here, but a test build
> > said it was OK.
> > 
> > Actually, I was expecting this patch series to depend on the linux-next
> > cgroup2 changes, but that doesn't appear to be the case.  *should* this
> > series be staged after the cgroup2 code?
> 
> Code-wise they are independent. My stuff is finishing up the new memcg
> control knobs, the cgroup2 stuff is changing how and when those knobs
> are exposed from within the cgroup core. I'm not relying on any recent
> changes in the cgroup core AFAICS, so the order shouldn't matter here.

OK, thanks.

> > Regarding this particular series: yes, I think we can live with a
> > bisection hole for !CONFIG_INET && CONFIG_MEMCG users.  But I'm not
> > sure why we're discussing bisection issues, because Arnd's build
> > failure occurs with everything applied?
> 
> Arnd's patches apply to the top of the stack, but they address issues
> introduced early in the series and the problematic code gets touched a
> lot in subsequent patches. E.g. the first build breakage is in ("net:
> tcp_memcontrol: simplify linkage between socket and page counter")
> when the tcp_init_cgroup() and tcp_destroy_cgroup() function calls get
> moved around and lose the CONFIG_INET protection.

Yeah, this is a pain.  I think I'll fold Arnd's fix into
mm-memcontrol-introduce-config_memcg_legacy_kmem.patch (which is staged
after all the other MM patches and after linux-next) and will pretend I
didn't know about the issue ;)

> Anyway, if we can live with the bisection caveat then Arnd's fixes on
> top of the kmem series look good to me. Depending on what Vladimir
> thinks we might want to replace the CONFIG_SLOB fix with something
> else later on, but that shouldn't be a problem, either.

I don't have a fix for the CONFIG_SLOB&&CONFIG_MEMCG issue yet.  I
agree that it would be best to make the combination work correctly
rather than banning it, but that does require a bit of runtime testing.

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