Re: [PATCH v2 1/2] hugetlb: memcg: account hugetlb-backed memory in memory controller

From: Nhat Pham
Date: Thu Sep 28 2023 - 20:33:31 EST

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On Thu, Sep 28, 2023 at 3:59 PM Frank van der Linden <fvdl@xxxxxxxxxx> wrote:
>
> On Wed, Sep 27, 2023 at 5:57 PM Nhat Pham <nphamcs@xxxxxxxxx> wrote:
>>
>> Currently, hugetlb memory usage is not acounted for in the memory
>> controller, which could lead to memory overprotection for cgroups with
>> hugetlb-backed memory. This has been observed in our production system.
>>
>> This patch rectifies this issue by charging the memcg when the hugetlb
>> folio is allocated, and uncharging when the folio is freed (analogous to
>> the hugetlb controller).
>>
>> Signed-off-by: Nhat Pham <nphamcs@xxxxxxxxx>
>> ---
>> Documentation/admin-guide/cgroup-v2.rst | 9 ++++++
>> fs/hugetlbfs/inode.c | 2 +-
>> include/linux/cgroup-defs.h | 5 +++
>> include/linux/hugetlb.h | 6 ++--
>> include/linux/memcontrol.h | 8 +++++
>> kernel/cgroup/cgroup.c | 15 ++++++++-
>> mm/hugetlb.c | 23 ++++++++++----
>> mm/memcontrol.c | 41 +++++++++++++++++++++++++
>> 8 files changed, 99 insertions(+), 10 deletions(-)
>>
>> diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
>> index 622a7f28db1f..e6267b8cbd1d 100644
>> --- a/Documentation/admin-guide/cgroup-v2.rst
>> +++ b/Documentation/admin-guide/cgroup-v2.rst
>> @@ -210,6 +210,15 @@ cgroup v2 currently supports the following mount options.
>> relying on the original semantics (e.g. specifying bogusly
>> high 'bypass' protection values at higher tree levels).
>>
>> + memory_hugetlb_accounting
>> + Count hugetlb memory usage towards the cgroup's overall
>> + memory usage for the memory controller. This is a new behavior
>> + that could regress existing setups, so it must be explicitly
>> + opted in with this mount option. Note that hugetlb pages
>> + allocated while this option is not selected will not be
>> + tracked by the memory controller (even if cgroup v2 is
>> + remounted later on).
>> +
>>
>> Organizing Processes and Threads
>> --------------------------------
>> diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
>> index 60fce26ff937..034967319955 100644
>> --- a/fs/hugetlbfs/inode.c
>> +++ b/fs/hugetlbfs/inode.c
>> @@ -902,7 +902,7 @@ static long hugetlbfs_fallocate(struct file *file, int mode, loff_t offset,
>> * to keep reservation accounting consistent.
>> */
>> hugetlb_set_vma_policy(&pseudo_vma, inode, index);
>> - folio = alloc_hugetlb_folio(&pseudo_vma, addr, 0);
>> + folio = alloc_hugetlb_folio(&pseudo_vma, addr, 0, true);
>> hugetlb_drop_vma_policy(&pseudo_vma);
>> if (IS_ERR(folio)) {
>> mutex_unlock(&hugetlb_fault_mutex_table[hash]);
>> diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
>> index f1b3151ac30b..8641f4320c98 100644
>> --- a/include/linux/cgroup-defs.h
>> +++ b/include/linux/cgroup-defs.h
>> @@ -115,6 +115,11 @@ enum {
>> * Enable recursive subtree protection
>> */
>> CGRP_ROOT_MEMORY_RECURSIVE_PROT = (1 << 18),
>> +
>> + /*
>> + * Enable hugetlb accounting for the memory controller.
>> + */
>> + CGRP_ROOT_MEMORY_HUGETLB_ACCOUNTING = (1 << 19),
>> };
>>
>> /* cftype->flags */
>> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
>> index a30686e649f7..9b73db1605a2 100644
>> --- a/include/linux/hugetlb.h
>> +++ b/include/linux/hugetlb.h
>> @@ -713,7 +713,8 @@ struct huge_bootmem_page {
>>
>> int isolate_or_dissolve_huge_page(struct page *page, struct list_head *list);
>> struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma,
>> - unsigned long addr, int avoid_reserve);
>> + unsigned long addr, int avoid_reserve,
>> + bool restore_reserve_on_memcg_failure);
>> struct folio *alloc_hugetlb_folio_nodemask(struct hstate *h, int preferred_nid,
>> nodemask_t *nmask, gfp_t gfp_mask);
>> struct folio *alloc_hugetlb_folio_vma(struct hstate *h, struct vm_area_struct *vma,
>> @@ -1016,7 +1017,8 @@ static inline int isolate_or_dissolve_huge_page(struct page *page,
>>
>> static inline struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma,
>> unsigned long addr,
>> - int avoid_reserve)
>> + int avoid_reserve,
>> + bool restore_reserve_on_memcg_failure)
>> {
>> return NULL;
>> }
>> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
>> index e0cfab58ab71..8094679c99dd 100644
>> --- a/include/linux/memcontrol.h
>> +++ b/include/linux/memcontrol.h
>> @@ -677,6 +677,8 @@ static inline int mem_cgroup_charge(struct folio *folio, struct mm_struct *mm,
>> return __mem_cgroup_charge(folio, mm, gfp);
>> }
>>
>> +int mem_cgroup_hugetlb_charge_folio(struct folio *folio, gfp_t gfp);
>> +
>> int mem_cgroup_swapin_charge_folio(struct folio *folio, struct mm_struct *mm,
>> gfp_t gfp, swp_entry_t entry);
>> void mem_cgroup_swapin_uncharge_swap(swp_entry_t entry);
>> @@ -1251,6 +1253,12 @@ static inline int mem_cgroup_charge(struct folio *folio,
>> return 0;
>> }
>>
>> +static inline int mem_cgroup_hugetlb_charge_folio(struct folio *folio,
>> + gfp_t gfp)
>> +{
>> + return 0;
>> +}
>> +
>> static inline int mem_cgroup_swapin_charge_folio(struct folio *folio,
>> struct mm_struct *mm, gfp_t gfp, swp_entry_t entry)
>> {
>> diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
>> index 1fb7f562289d..f11488b18ceb 100644
>> --- a/kernel/cgroup/cgroup.c
>> +++ b/kernel/cgroup/cgroup.c
>> @@ -1902,6 +1902,7 @@ enum cgroup2_param {
>> Opt_favordynmods,
>> Opt_memory_localevents,
>> Opt_memory_recursiveprot,
>> + Opt_memory_hugetlb_accounting,
>> nr__cgroup2_params
>> };
>>
>> @@ -1910,6 +1911,7 @@ static const struct fs_parameter_spec cgroup2_fs_parameters[] = {
>> fsparam_flag("favordynmods", Opt_favordynmods),
>> fsparam_flag("memory_localevents", Opt_memory_localevents),
>> fsparam_flag("memory_recursiveprot", Opt_memory_recursiveprot),
>> + fsparam_flag("memory_hugetlb_accounting", Opt_memory_hugetlb_accounting),
>> {}
>> };
>>
>> @@ -1936,6 +1938,9 @@ static int cgroup2_parse_param(struct fs_context *fc, struct fs_parameter *param
>> case Opt_memory_recursiveprot:
>> ctx->flags |= CGRP_ROOT_MEMORY_RECURSIVE_PROT;
>> return 0;
>> + case Opt_memory_hugetlb_accounting:
>> + ctx->flags |= CGRP_ROOT_MEMORY_HUGETLB_ACCOUNTING;
>> + return 0;
>> }
>> return -EINVAL;
>> }
>> @@ -1960,6 +1965,11 @@ static void apply_cgroup_root_flags(unsigned int root_flags)
>> cgrp_dfl_root.flags |= CGRP_ROOT_MEMORY_RECURSIVE_PROT;
>> else
>> cgrp_dfl_root.flags &= ~CGRP_ROOT_MEMORY_RECURSIVE_PROT;
>> +
>> + if (root_flags & CGRP_ROOT_MEMORY_HUGETLB_ACCOUNTING)
>> + cgrp_dfl_root.flags |= CGRP_ROOT_MEMORY_HUGETLB_ACCOUNTING;
>> + else
>> + cgrp_dfl_root.flags &= ~CGRP_ROOT_MEMORY_HUGETLB_ACCOUNTING;
>> }
>> }
>>
>> @@ -1973,6 +1983,8 @@ static int cgroup_show_options(struct seq_file *seq, struct kernfs_root *kf_root
>> seq_puts(seq, ",memory_localevents");
>> if (cgrp_dfl_root.flags & CGRP_ROOT_MEMORY_RECURSIVE_PROT)
>> seq_puts(seq, ",memory_recursiveprot");
>> + if (cgrp_dfl_root.flags & CGRP_ROOT_MEMORY_HUGETLB_ACCOUNTING)
>> + seq_puts(seq, ",memory_hugetlb_accounting");
>> return 0;
>> }
>>
>> @@ -7050,7 +7062,8 @@ static ssize_t features_show(struct kobject *kobj, struct kobj_attribute *attr,
>> "nsdelegate\n"
>> "favordynmods\n"
>> "memory_localevents\n"
>> - "memory_recursiveprot\n");
>> + "memory_recursiveprot\n"
>> + "memory_hugetlb_accounting\n");
>> }
>> static struct kobj_attribute cgroup_features_attr = __ATTR_RO(features);
>>
>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
>> index de220e3ff8be..ff88ea4df11a 100644
>> --- a/mm/hugetlb.c
>> +++ b/mm/hugetlb.c
>> @@ -1902,6 +1902,7 @@ void free_huge_folio(struct folio *folio)
>> pages_per_huge_page(h), folio);
>> hugetlb_cgroup_uncharge_folio_rsvd(hstate_index(h),
>> pages_per_huge_page(h), folio);
>> + mem_cgroup_uncharge(folio);
>> if (restore_reserve)
>> h->resv_huge_pages++;
>>
>> @@ -3004,7 +3005,8 @@ int isolate_or_dissolve_huge_page(struct page *page, struct list_head *list)
>> }
>>
>> struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma,
>> - unsigned long addr, int avoid_reserve)
>> + unsigned long addr, int avoid_reserve,
>> + bool restore_reserve_on_memcg_failure)
>> {
>> struct hugepage_subpool *spool = subpool_vma(vma);
>> struct hstate *h = hstate_vma(vma);
>> @@ -3119,6 +3121,15 @@ struct folio *alloc_hugetlb_folio(struct vm_area_struct *vma,
>> hugetlb_cgroup_uncharge_folio_rsvd(hstate_index(h),
>> pages_per_huge_page(h), folio);
>> }
>> +
>> + /* undo allocation if memory controller disallows it. */
>> + if (mem_cgroup_hugetlb_charge_folio(folio, GFP_KERNEL)) {
>> + if (restore_reserve_on_memcg_failure)
>> + restore_reserve_on_error(h, vma, addr, folio);
>> + folio_put(folio);
>> + return ERR_PTR(-ENOMEM);
>> + }
>> +
>> return folio;
>>
>> out_uncharge_cgroup:
>> @@ -5179,7 +5190,7 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
>> spin_unlock(src_ptl);
>> spin_unlock(dst_ptl);
>> /* Do not use reserve as it's private owned */
>> - new_folio = alloc_hugetlb_folio(dst_vma, addr, 1);
>> + new_folio = alloc_hugetlb_folio(dst_vma, addr, 1, false);
>> if (IS_ERR(new_folio)) {
>> folio_put(pte_folio);
>> ret = PTR_ERR(new_folio);
>> @@ -5656,7 +5667,7 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma,
>> * be acquired again before returning to the caller, as expected.
>> */
>> spin_unlock(ptl);
>> - new_folio = alloc_hugetlb_folio(vma, haddr, outside_reserve);
>> + new_folio = alloc_hugetlb_folio(vma, haddr, outside_reserve, true);
>>
>> if (IS_ERR(new_folio)) {
>> /*
>> @@ -5930,7 +5941,7 @@ static vm_fault_t hugetlb_no_page(struct mm_struct *mm,
>> VM_UFFD_MISSING);
>> }
>>
>> - folio = alloc_hugetlb_folio(vma, haddr, 0);
>> + folio = alloc_hugetlb_folio(vma, haddr, 0, true);
>> if (IS_ERR(folio)) {
>> /*
>> * Returning error will result in faulting task being
>> @@ -6352,7 +6363,7 @@ int hugetlb_mfill_atomic_pte(pte_t *dst_pte,
>> goto out;
>> }
>>
>> - folio = alloc_hugetlb_folio(dst_vma, dst_addr, 0);
>> + folio = alloc_hugetlb_folio(dst_vma, dst_addr, 0, true);
>> if (IS_ERR(folio)) {
>> ret = -ENOMEM;
>> goto out;
>> @@ -6394,7 +6405,7 @@ int hugetlb_mfill_atomic_pte(pte_t *dst_pte,
>> goto out;
>> }
>>
>> - folio = alloc_hugetlb_folio(dst_vma, dst_addr, 0);
>> + folio = alloc_hugetlb_folio(dst_vma, dst_addr, 0, false);
>> if (IS_ERR(folio)) {
>> folio_put(*foliop);
>> ret = -ENOMEM;
>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>> index d1a322a75172..d5dfc9b36acb 100644
>> --- a/mm/memcontrol.c
>> +++ b/mm/memcontrol.c
>> @@ -7050,6 +7050,47 @@ int __mem_cgroup_charge(struct folio *folio, struct mm_struct *mm, gfp_t gfp)
>> return ret;
>> }
>>
>> +static struct mem_cgroup *get_mem_cgroup_from_current(void)
>> +{
>> + struct mem_cgroup *memcg;
>> +
>> +again:
>> + rcu_read_lock();
>> + memcg = mem_cgroup_from_task(current);
>> + if (!css_tryget(&memcg->css)) {
>> + rcu_read_unlock();
>> + goto again;
>> + }
>> + rcu_read_unlock();
>> + return memcg;
>> +}
>> +
>> +/**
>> + * mem_cgroup_hugetlb_charge_folio - Charge a newly allocated hugetlb folio.
>> + * @folio: folio to charge.
>> + * @gfp: reclaim mode
>> + *
>> + * This function charges an allocated hugetlbf folio to the memcg of the
>> + * current task.
>> + *
>> + * Returns 0 on success. Otherwise, an error code is returned.
>> + */
>> +int mem_cgroup_hugetlb_charge_folio(struct folio *folio, gfp_t gfp)
>> +{
>> + struct mem_cgroup *memcg;
>> + int ret;
>> +
>> + if (mem_cgroup_disabled() ||
>> + !(cgrp_dfl_root.flags & CGRP_ROOT_MEMORY_HUGETLB_ACCOUNTING))
>> + return 0;
>> +
>> + memcg = get_mem_cgroup_from_current();
>> + ret = charge_memcg(folio, memcg, gfp);
>> + mem_cgroup_put(memcg);
>> +
>> + return ret;
>> +}
>> +
>> /**
>> * mem_cgroup_swapin_charge_folio - Charge a newly allocated folio for swapin.
>> * @folio: folio to charge.
>> --
>> 2.34.1
>>
>
> With the mount option added, I'm fine with this. There are reasons to want and reasons not to want this, so everybody's happy!

And the default is no accounting, so this should be safe on impact!

>
> Out of curiosity: is anyone aware of any code that may behave badly when folio_memcg(hugetlb_folio) != NULL, not expecting it?

Good point. My understanding of the memory controller mechanism
is that it should be fine - we're just essentially storing some memcg
metadata in the struct folio, and then charging values towards the
memcg counters. I don't think we fiddle with anything else in
the folio itself that could be ruinous?

I also did my best to trace the code paths that go through
alloc_hugetlb_folio and free_huge_folio (the places where charging
and uncharging happens) to make sure no funny business is going
on, and it seems a lot of these paths have special, dedicated handling
for hugetlb folio. The usual pattern is checking if the folio is a hugetlb
one first, so we're unlikely to even call folio_memcg on a hugetlb
folio in existing code in the first place.

But if anyone knows something I missed please let me know!
And feel free to loop more people in if there's anyone I miss in
the cc list :)

>
> - Frank

Next message: Yosry Ahmed: "Re: [PATCH v2 1/2] hugetlb: memcg: account hugetlb-backed memory in memory controller"
Previous message: Thomas Gleixner: "Re: [PATCH 1/3] SCHEDULER: Add an interface for counting real utilization."
In reply to: Nhat Pham: "[PATCH v2 1/2] hugetlb: memcg: account hugetlb-backed memory in memory controller"
Next in thread: Yosry Ahmed: "Re: [PATCH v2 1/2] hugetlb: memcg: account hugetlb-backed memory in memory controller"
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