Messages in this thread | | | From | Waiman Long <> | Subject | Re: [PATCH v4 2/3] mm: memcg/slab: Create a new set of kmalloc-cg-<n> caches | Date | Fri, 7 May 2021 14:45:48 -0400 |
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On 5/6/21 12:00 PM, Vlastimil Babka wrote: > On 5/5/21 10:06 PM, Waiman Long wrote: >> There are currently two problems in the way the objcg pointer array >> (memcg_data) in the page structure is being allocated and freed. >> >> On its allocation, it is possible that the allocated objcg pointer >> array comes from the same slab that requires memory accounting. If this >> happens, the slab will never become empty again as there is at least >> one object left (the obj_cgroup array) in the slab. >> >> When it is freed, the objcg pointer array object may be the last one >> in its slab and hence causes kfree() to be called again. With the >> right workload, the slab cache may be set up in a way that allows the >> recursive kfree() calling loop to nest deep enough to cause a kernel >> stack overflow and panic the system. >> >> One way to solve this problem is to split the kmalloc-<n> caches >> (KMALLOC_NORMAL) into two separate sets - a new set of kmalloc-<n> >> (KMALLOC_NORMAL) caches for unaccounted objects only and a new set of >> kmalloc-cg-<n> (KMALLOC_CGROUP) caches for accounted objects only. All >> the other caches can still allow a mix of accounted and unaccounted >> objects. >> >> With this change, all the objcg pointer array objects will come from >> KMALLOC_NORMAL caches which won't have their objcg pointer arrays. So >> both the recursive kfree() problem and non-freeable slab problem are >> gone. >> >> Since both the KMALLOC_NORMAL and KMALLOC_CGROUP caches no longer have >> mixed accounted and unaccounted objects, this will slightly reduce the >> number of objcg pointer arrays that need to be allocated and save a bit >> of memory. On the other hand, creating a new set of kmalloc caches does >> have the effect of reducing cache utilization. So it is properly a wash. >> >> The new KMALLOC_CGROUP is added between KMALLOC_NORMAL and >> KMALLOC_RECLAIM so that the first for loop in create_kmalloc_caches() >> will include the newly added caches without change. >> >> Suggested-by: Vlastimil Babka <vbabka@suse.cz> >> Signed-off-by: Waiman Long <longman@redhat.com> >> Reviewed-by: Shakeel Butt <shakeelb@google.com> > Reviewed-by: Vlastimil Babka <vbabka@suse.cz> > > I still believe the cgroup.memory=nokmem parameter should be respected, > otherwise the caches are not only created, but also used. I offer this followup > for squashing into your patch if you and Andrew agree: > > ----8<---- > From c87378d437d9a59b8757033485431b4721c74173 Mon Sep 17 00:00:00 2001 > From: Vlastimil Babka <vbabka@suse.cz> > Date: Thu, 6 May 2021 17:53:21 +0200 > Subject: [PATCH] mm: memcg/slab: don't create kmalloc-cg caches with > cgroup.memory=nokmem > > The caches should not be created when kmemcg is disabled on boot, otherwise > they are also filled by kmalloc(__GFP_ACCOUNT) allocations. When booted with > cgroup.memory=nokmem, link the kmalloc_caches[KMALLOC_CGROUP] entries to > KMALLOC_NORMAL entries instead. > > Signed-off-by: Vlastimil Babka <vbabka@suse.cz> > --- > mm/internal.h | 5 +++++ > mm/memcontrol.c | 2 +- > mm/slab_common.c | 9 +++++++-- > 3 files changed, 13 insertions(+), 3 deletions(-) > > diff --git a/mm/internal.h b/mm/internal.h > index ef5f336f59bd..b2d60b3403c7 100644 > --- a/mm/internal.h > +++ b/mm/internal.h > @@ -135,6 +135,11 @@ extern void putback_lru_page(struct page *page); > */ > extern pmd_t *mm_find_pmd(struct mm_struct *mm, unsigned long address); > > +/* > + * in mm/memcontrol.c: > + */ > +extern bool cgroup_memory_nokmem; > + > /* > * in mm/page_alloc.c > */ > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 5e3b4f23b830..b9ec01f2b4f6 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -83,7 +83,7 @@ DEFINE_PER_CPU(struct mem_cgroup *, int_active_memcg); > static bool cgroup_memory_nosocket; > > /* Kernel memory accounting disabled? */ > -static bool cgroup_memory_nokmem; > +bool cgroup_memory_nokmem; > > /* Whether the swap controller is active */ > #ifdef CONFIG_MEMCG_SWAP > diff --git a/mm/slab_common.c b/mm/slab_common.c > index bbaf41a7c77e..363f90215401 100644 > --- a/mm/slab_common.c > +++ b/mm/slab_common.c > @@ -832,10 +832,15 @@ void __init setup_kmalloc_cache_index_table(void) > static void __init > new_kmalloc_cache(int idx, enum kmalloc_cache_type type, slab_flags_t flags) > { > - if (type == KMALLOC_RECLAIM) > + if (type == KMALLOC_RECLAIM) { > flags |= SLAB_RECLAIM_ACCOUNT; > - else if (IS_ENABLED(CONFIG_MEMCG_KMEM) && (type == KMALLOC_CGROUP)) > + } else if (IS_ENABLED(CONFIG_MEMCG_KMEM) && (type == KMALLOC_CGROUP)) { > + if (cgroup_memory_nokmem) { > + kmalloc_caches[type][idx] = kmalloc_caches[KMALLOC_NORMAL][idx]; > + return; > + } > flags |= SLAB_ACCOUNT; > + } > > kmalloc_caches[type][idx] = create_kmalloc_cache( > kmalloc_info[idx].name[type],
Thanks, the patch looks good to me.
Acked-by: Waiman Long <longman@redhat.com>
Cheers, Longman
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