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Date: Mon, 30 Nov 2015 20:08:31 +0300
From: Vladimir Davydov <vdavydov@...tuozzo.com>
To: Johannes Weiner <hannes@...xchg.org>
CC: Andrew Morton <akpm@...ux-foundation.org>,
David Miller <davem@...emloft.net>,
Michal Hocko <mhocko@...e.cz>, Tejun Heo <tj@...nel.org>,
Eric Dumazet <eric.dumazet@...il.com>,
<netdev@...r.kernel.org>, <linux-mm@...ck.org>,
<cgroups@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
<kernel-team@...com>
Subject: Re: [PATCH 12/13] mm: memcontrol: account socket memory in unified
hierarchy memory controller
On Mon, Nov 30, 2015 at 10:26:38AM -0500, Johannes Weiner wrote:
> On Mon, Nov 30, 2015 at 01:54:21PM +0300, Vladimir Davydov wrote:
> > On Tue, Nov 24, 2015 at 04:58:44PM -0500, Johannes Weiner wrote:
> > ...
> > > @@ -5520,15 +5557,30 @@ void sock_release_memcg(struct sock *sk)
> > > */
> > > bool mem_cgroup_charge_skmem(struct mem_cgroup *memcg, unsigned int nr_pages)
> > > {
> > > - struct page_counter *counter;
> > > + gfp_t gfp_mask = GFP_KERNEL;
> > >
> > > - if (page_counter_try_charge(&memcg->tcp_mem.memory_allocated,
> > > - nr_pages, &counter)) {
> > > - memcg->tcp_mem.memory_pressure = 0;
> > > - return true;
> > > +#ifdef CONFIG_MEMCG_KMEM
> > > + if (!cgroup_subsys_on_dfl(memory_cgrp_subsys)) {
> > > + struct page_counter *counter;
> > > +
> > > + if (page_counter_try_charge(&memcg->tcp_mem.memory_allocated,
> > > + nr_pages, &counter)) {
> > > + memcg->tcp_mem.memory_pressure = 0;
> > > + return true;
> > > + }
> > > + page_counter_charge(&memcg->tcp_mem.memory_allocated, nr_pages);
> > > + memcg->tcp_mem.memory_pressure = 1;
> > > + return false;
> > > }
> > > - page_counter_charge(&memcg->tcp_mem.memory_allocated, nr_pages);
> > > - memcg->tcp_mem.memory_pressure = 1;
> > > +#endif
> > > + /* Don't block in the packet receive path */
> > > + if (in_softirq())
> > > + gfp_mask = GFP_NOWAIT;
> > > +
> > > + if (try_charge(memcg, gfp_mask, nr_pages) == 0)
> > > + return true;
> > > +
> > > + try_charge(memcg, gfp_mask|__GFP_NOFAIL, nr_pages);
> >
> > We won't trigger high reclaim if we get here, because try_charge does
> > not check high threshold if failing or forcing charge. I think this
> > should be fixed regardless of this patch. The fix is attached below.
>
> We kind of assume that max is either set above high, or not at
> all. That means when max is hit the high limit has already failed and
> it's of limited use to schedule background reclaim.
Yeah, you're right. No point scheduling the work here - it must be
already running.
>
> > Also, I don't like calling try_charge twice: the second time will go
> > through all the try_charge steps for nothing. What about checking
> > page_counter value after calling try_charge instead:
> >
> > try_charge(memcg, gfp_mask|__GFP_NOFAIL, nr_pages);
> > return page_counter_read(&memcg->memory) <= memcg->memory.limit;
> >
> > or adding an out parameter to try_charge that would inform us if charge
> > was forced?
>
> That's a complete cold path where we are going to drop the packet in
> all but a few cases. It's not worth the trouble.
Right
>
> > > @@ -5539,10 +5591,32 @@ bool mem_cgroup_charge_skmem(struct mem_cgroup *memcg, unsigned int nr_pages)
> > > */
> > > void mem_cgroup_uncharge_skmem(struct mem_cgroup *memcg, unsigned int nr_pages)
> > > {
> > > - page_counter_uncharge(&memcg->tcp_mem.memory_allocated, nr_pages);
> > > +#ifdef CONFIG_MEMCG_KMEM
> > > + if (!cgroup_subsys_on_dfl(memory_cgrp_subsys)) {
> > > + page_counter_uncharge(&memcg->tcp_mem.memory_allocated,
> > > + nr_pages);
> > > + return;
> > > + }
> > > +#endif
> > > + page_counter_uncharge(&memcg->memory, nr_pages);
> > > + css_put_many(&memcg->css, nr_pages);
> >
> > cancel_charge(memcg, nr_pages);
>
> It does the same, but it's a weird name for regular uncharging.
Right
>
> > From: Vladimir Davydov <vdavydov@...tuozzo.com>
> > Subject: [PATCH] memcg: check high threshold if forcing allocation
> >
> > try_charge() does not result in checking high threshold if it forces
> > charge. This is incorrect, because we could have failed to reclaim
> > memory due to the current context, so we do need to check high threshold
> > and try to compensate for the excess once we are in the safe context.
> >
> > Signed-off-by: Vladimir Davydov <vdavydov@...tuozzo.com>
> >
> > diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> > index 79a29d564bff..e922965b572b 100644
> > --- a/mm/memcontrol.c
> > +++ b/mm/memcontrol.c
> > @@ -2112,13 +2112,14 @@ static int try_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
> > page_counter_charge(&memcg->memsw, nr_pages);
> > css_get_many(&memcg->css, nr_pages);
> >
> > - return 0;
> > + goto check_high;
> >
> > done_restock:
> > css_get_many(&memcg->css, batch);
> > if (batch > nr_pages)
> > refill_stock(memcg, batch - nr_pages);
> >
> > +check_high:
> > /*
> > * If the hierarchy is above the normal consumption range, schedule
> > * reclaim on returning to userland. We can perform reclaim here
>
> One problem is that OOM victims force their charges so they can exit
> quickly. It'd be contradictory to then task them with high reclaim.
>
Yeah, scratch that patch. It isn't necessary anyway, because, as you
pointed out, we don't really need to schedule high reclaim when we fail
hard in mem_cgroup_charge_skmem.
No more questions left,
Reviewed-by: Vladimir Davydov <vdavydov@...tuozzo.com>
Thanks,
Vladimir
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