From: Roman Gushchin <guro@fb.com>
To: Johannes Weiner <hannes@cmpxchg.org>
Cc: <linux-mm@kvack.org>, Andrew Morton <akpm@linux-foundation.org>,
Michal Hocko <mhocko@kernel.org>,
Shakeel Butt <shakeelb@google.com>,
Vladimir Davydov <vdavydov.dev@gmail.com>,
<linux-kernel@vger.kernel.org>, <kernel-team@fb.com>,
Bharata B Rao <bharata@linux.ibm.com>,
Yafang Shao <laoar.shao@gmail.com>
Subject: Re: [PATCH v2 16/28] mm: memcg/slab: allocate obj_cgroups for non-root slab pages
Date: Mon, 3 Feb 2020 13:19:15 -0800 [thread overview]
Message-ID: <20200203211915.GB6781@xps.dhcp.thefacebook.com> (raw)
In-Reply-To: <20200203204627.GB6380@cmpxchg.org>
On Mon, Feb 03, 2020 at 03:46:27PM -0500, Johannes Weiner wrote:
> On Mon, Feb 03, 2020 at 10:34:52AM -0800, Roman Gushchin wrote:
> > On Mon, Feb 03, 2020 at 01:27:56PM -0500, Johannes Weiner wrote:
> > > On Mon, Jan 27, 2020 at 09:34:41AM -0800, Roman Gushchin wrote:
> > > > Allocate and release memory to store obj_cgroup pointers for each
> > > > non-root slab page. Reuse page->mem_cgroup pointer to store a pointer
> > > > to the allocated space.
> > > >
> > > > To distinguish between obj_cgroups and memcg pointers in case
> > > > when it's not obvious which one is used (as in page_cgroup_ino()),
> > > > let's always set the lowest bit in the obj_cgroup case.
> > > >
> > > > Signed-off-by: Roman Gushchin <guro@fb.com>
> > > > ---
> > > > include/linux/mm.h | 25 ++++++++++++++++++--
> > > > include/linux/mm_types.h | 5 +++-
> > > > mm/memcontrol.c | 5 ++--
> > > > mm/slab.c | 3 ++-
> > > > mm/slab.h | 51 +++++++++++++++++++++++++++++++++++++++-
> > > > mm/slub.c | 2 +-
> > > > 6 files changed, 83 insertions(+), 8 deletions(-)
> > > >
> > > > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > > > index 080f8ac8bfb7..65224becc4ca 100644
> > > > --- a/include/linux/mm.h
> > > > +++ b/include/linux/mm.h
> > > > @@ -1264,12 +1264,33 @@ static inline void set_page_links(struct page *page, enum zone_type zone,
> > > > #ifdef CONFIG_MEMCG
> > > > static inline struct mem_cgroup *page_memcg(struct page *page)
> > > > {
> > > > - return page->mem_cgroup;
> > > > + struct mem_cgroup *memcg = page->mem_cgroup;
> > > > +
> > > > + /*
> > > > + * The lowest bit set means that memcg isn't a valid memcg pointer,
> > > > + * but a obj_cgroups pointer. In this case the page is shared and
> > > > + * isn't charged to any specific memory cgroup. Return NULL.
> > > > + */
> > > > + if ((unsigned long) memcg & 0x1UL)
> > > > + memcg = NULL;
> > > > +
> > > > + return memcg;
> > >
> > > That should really WARN instead of silently returning NULL. Which
> > > callsite optimistically asks a page's cgroup when it has no idea
> > > whether that page is actually a userpage or not?
> >
> > For instance, look at page_cgroup_ino() called from the
> > reading /proc/kpageflags.
>
> But that checks PageSlab() and implements memcg_from_slab_page() to
> handle that case properly. And that's what we expect all callsites to
> do: make sure that the question asked actually makes sense, instead of
> having the interface paper over bogus requests.
>
> If that function is completely racy and PageSlab isn't stable, then it
> should really just open-code the lookup, rather than require weakening
> the interface for everybody else.
Why though?
Another example: process stack can be depending on the machine config and
platform a vmalloc allocation, a slab allocation or a "high-order slab allocation",
which is executed by the page allocator directly.
It's kinda nice to have a function that hides accounting details
and returns a valid memcg pointer for any kind of objects.
To me it seems to be a valid question:
for a given kernel object give me a pointer to the memory cgroup.
Why it's weakening?
Moreover, open-coding of this question leads to bugs like one fixed by
ec9f02384f60 ("mm: workingset: fix vmstat counters for shadow nodes").
>
> > > > static inline struct mem_cgroup *page_memcg_rcu(struct page *page)
> > > > {
> > > > + struct mem_cgroup *memcg = READ_ONCE(page->mem_cgroup);
> > > > +
> > > > WARN_ON_ONCE(!rcu_read_lock_held());
> > > > - return READ_ONCE(page->mem_cgroup);
> > > > +
> > > > + /*
> > > > + * The lowest bit set means that memcg isn't a valid memcg pointer,
> > > > + * but a obj_cgroups pointer. In this case the page is shared and
> > > > + * isn't charged to any specific memory cgroup. Return NULL.
> > > > + */
> > > > + if ((unsigned long) memcg & 0x1UL)
> > > > + memcg = NULL;
> > > > +
> > > > + return memcg;
> > >
> > > Same here.
> > >
> > > > }
> > > > #else
> > > > static inline struct mem_cgroup *page_memcg(struct page *page)
> > > > diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> > > > index 270aa8fd2800..5102f00f3336 100644
> > > > --- a/include/linux/mm_types.h
> > > > +++ b/include/linux/mm_types.h
> > > > @@ -198,7 +198,10 @@ struct page {
> > > > atomic_t _refcount;
> > > >
> > > > #ifdef CONFIG_MEMCG
> > > > - struct mem_cgroup *mem_cgroup;
> > > > + union {
> > > > + struct mem_cgroup *mem_cgroup;
> > > > + struct obj_cgroup **obj_cgroups;
> > > > + };
> > >
> > > Since you need the casts in both cases anyway, it's safer (and
> > > simpler) to do
> > >
> > > unsigned long mem_cgroup;
> > >
> > > to prevent accidental direct derefs in future code.
> >
> > Agree. Maybe even mem_cgroup_data?
>
> Personally, I don't think the suffix adds much. The type makes it so
> the compiler catches any accidental use, and access is very
> centralized so greppability doesn't matter much.
next prev parent reply other threads:[~2020-02-03 21:19 UTC|newest]
Thread overview: 84+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-27 17:34 [PATCH v2 00/28] The new cgroup slab memory controller Roman Gushchin
2020-01-27 17:34 ` [PATCH v2 01/28] mm: kmem: cleanup (__)memcg_kmem_charge_memcg() arguments Roman Gushchin
2020-01-27 17:34 ` [PATCH v2 02/28] mm: kmem: cleanup memcg_kmem_uncharge_memcg() arguments Roman Gushchin
2020-01-27 17:34 ` [PATCH v2 03/28] mm: kmem: rename memcg_kmem_(un)charge() into memcg_kmem_(un)charge_page() Roman Gushchin
2020-01-27 17:34 ` [PATCH v2 04/28] mm: kmem: switch to nr_pages in (__)memcg_kmem_charge_memcg() Roman Gushchin
2020-01-27 17:34 ` [PATCH v2 05/28] mm: memcg/slab: cache page number in memcg_(un)charge_slab() Roman Gushchin
2020-01-27 17:34 ` [PATCH v2 06/28] mm: kmem: rename (__)memcg_kmem_(un)charge_memcg() to __memcg_kmem_(un)charge() Roman Gushchin
2020-01-27 17:34 ` [PATCH v2 07/28] mm: memcg/slab: introduce mem_cgroup_from_obj() Roman Gushchin
2020-02-03 16:05 ` Johannes Weiner
2020-01-27 17:34 ` [PATCH v2 08/28] mm: fork: fix kernel_stack memcg stats for various stack implementations Roman Gushchin
2020-02-03 16:12 ` Johannes Weiner
2020-01-27 17:34 ` [PATCH v2 09/28] mm: memcg/slab: rename __mod_lruvec_slab_state() into __mod_lruvec_obj_state() Roman Gushchin
2020-02-03 16:13 ` Johannes Weiner
2020-01-27 17:34 ` [PATCH v2 10/28] mm: memcg: introduce mod_lruvec_memcg_state() Roman Gushchin
2020-02-03 17:39 ` Johannes Weiner
2020-01-27 17:34 ` [PATCH v2 11/28] mm: slub: implement SLUB version of obj_to_index() Roman Gushchin
2020-02-03 17:44 ` Johannes Weiner
2020-01-27 17:34 ` [PATCH v2 12/28] mm: vmstat: use s32 for vm_node_stat_diff in struct per_cpu_nodestat Roman Gushchin
2020-02-03 17:58 ` Johannes Weiner
2020-02-03 18:25 ` Roman Gushchin
2020-02-03 20:34 ` Johannes Weiner
2020-02-03 22:28 ` Roman Gushchin
2020-02-03 22:39 ` Johannes Weiner
2020-02-04 1:44 ` Roman Gushchin
2020-01-27 17:34 ` [PATCH v2 13/28] mm: vmstat: convert slab vmstat counter to bytes Roman Gushchin
2020-01-27 17:34 ` [PATCH v2 14/28] mm: memcontrol: decouple reference counting from page accounting Roman Gushchin
2020-01-27 17:34 ` [PATCH v2 15/28] mm: memcg/slab: obj_cgroup API Roman Gushchin
2020-02-03 19:31 ` Johannes Weiner
2020-01-27 17:34 ` [PATCH v2 16/28] mm: memcg/slab: allocate obj_cgroups for non-root slab pages Roman Gushchin
2020-02-03 18:27 ` Johannes Weiner
2020-02-03 18:34 ` Roman Gushchin
2020-02-03 20:46 ` Johannes Weiner
2020-02-03 21:19 ` Roman Gushchin [this message]
2020-02-03 22:29 ` Johannes Weiner
2020-01-27 17:34 ` [PATCH v2 17/28] mm: memcg/slab: save obj_cgroup for non-root slab objects Roman Gushchin
2020-02-03 19:53 ` Johannes Weiner
2020-01-27 17:34 ` [PATCH v2 18/28] mm: memcg/slab: charge individual slab objects instead of pages Roman Gushchin
2020-01-27 17:34 ` [PATCH v2 19/28] mm: memcg/slab: deprecate memory.kmem.slabinfo Roman Gushchin
2020-01-27 17:34 ` [PATCH v2 20/28] mm: memcg/slab: move memcg_kmem_bypass() to memcontrol.h Roman Gushchin
2020-01-27 17:34 ` [PATCH v2 21/28] mm: memcg/slab: use a single set of kmem_caches for all memory cgroups Roman Gushchin
2020-02-03 19:50 ` Johannes Weiner
2020-02-03 20:58 ` Roman Gushchin
2020-02-03 22:17 ` Johannes Weiner
2020-02-03 22:38 ` Roman Gushchin
2020-02-04 1:15 ` Roman Gushchin
2020-02-04 2:47 ` Johannes Weiner
2020-02-04 4:35 ` Roman Gushchin
2020-02-04 18:41 ` Johannes Weiner
2020-02-05 15:58 ` Roman Gushchin
2020-01-27 17:34 ` [PATCH v2 22/28] mm: memcg/slab: simplify memcg cache creation Roman Gushchin
2020-01-27 17:34 ` [PATCH v2 23/28] mm: memcg/slab: deprecate memcg_kmem_get_cache() Roman Gushchin
2020-01-27 17:34 ` [PATCH v2 24/28] mm: memcg/slab: deprecate slab_root_caches Roman Gushchin
2020-01-27 17:34 ` [PATCH v2 25/28] mm: memcg/slab: remove redundant check in memcg_accumulate_slabinfo() Roman Gushchin
2020-01-27 17:34 ` [PATCH v2 26/28] tools/cgroup: add slabinfo.py tool Roman Gushchin
2020-01-27 17:34 ` [PATCH v2 27/28] tools/cgroup: make slabinfo.py compatible with new slab controller Roman Gushchin
2020-01-30 2:17 ` Bharata B Rao
2020-01-30 2:44 ` Roman Gushchin
2020-01-31 22:24 ` Roman Gushchin
2020-02-12 5:21 ` Bharata B Rao
2020-02-12 20:42 ` Roman Gushchin
2020-01-27 17:34 ` [PATCH v2 28/28] kselftests: cgroup: add kernel memory accounting tests Roman Gushchin
2020-01-30 2:06 ` [PATCH v2 00/28] The new cgroup slab memory controller Bharata B Rao
2020-01-30 2:41 ` Roman Gushchin
2020-08-12 23:16 ` Pavel Tatashin
2020-08-12 23:18 ` Pavel Tatashin
2020-08-13 0:04 ` Roman Gushchin
2020-08-13 0:31 ` Pavel Tatashin
2020-08-28 16:47 ` Pavel Tatashin
2020-09-01 5:28 ` Bharata B Rao
2020-09-01 12:52 ` Pavel Tatashin
2020-09-02 6:23 ` Bharata B Rao
2020-09-02 12:34 ` Pavel Tatashin
2020-09-02 9:53 ` Vlastimil Babka
2020-09-02 10:39 ` David Hildenbrand
2020-09-02 12:42 ` Pavel Tatashin
2020-09-02 13:50 ` Michal Hocko
2020-09-02 14:20 ` Pavel Tatashin
2020-09-03 18:09 ` David Hildenbrand
2020-09-02 11:26 ` Michal Hocko
2020-09-02 12:51 ` Pavel Tatashin
2020-09-02 13:51 ` Michal Hocko
2020-09-02 11:32 ` Michal Hocko
2020-09-02 12:53 ` Pavel Tatashin
2020-09-02 13:52 ` Michal Hocko
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