[QUESTION] memcg page_counter seems broken in MADV_DONTNEED with THP enabled

[QUESTION] memcg page_counter seems broken in MADV_DONTNEED with THP enabled

[Yongqiang Liu]

Hi,

We use mm_counter to how much a process physical memory used. Meanwhile,
page_counter of a memcg is used to count how much a cgroup physical 
memory used.
If a cgroup only contains a process, they looks almost the same. But with
THP enabled, sometimes memory.usage_in_bytes in memcg may be twice or 
more than rss
in proc/[pid]/smaps_rollup as follow:

[root@localhost sda]# cat /sys/fs/cgroup/memory/test/memory.usage_in_bytes
1080930304
[root@localhost sda]# cat /sys/fs/cgroup/memory/test/cgroup.procs
1290
[root@localhost sda]# cat /proc/1290/smaps_rollup
55ba80600000-ffffffffff601000 ---p 00000000 00:00 0                      
[rollup]
Rss:              500648 kB
Pss:              498337 kB
Shared_Clean:       2732 kB
Shared_Dirty:          0 kB
Private_Clean:       364 kB
Private_Dirty:    497552 kB
Referenced:       500648 kB
Anonymous:        492016 kB
LazyFree:              0 kB
AnonHugePages:    129024 kB
ShmemPmdMapped:        0 kB
Shared_Hugetlb:        0 kB
Private_Hugetlb:       0 kB
Swap:                  0 kB
SwapPss:               0 kB
Locked:                0 kB
THPeligible:    0

I have found the differences was because that __split_huge_pmd decrease
the mm_counter but page_counter in memcg was not decreased with refcount
of a head page is not zero. Here are the follows:

do_madvise
   madvise_dontneed_free
     zap_page_range
       unmap_single_vma
         zap_pud_range
           zap_pmd_range
             __split_huge_pmd
               __split_huge_pmd_locked
                 __mod_lruvec_page_state
             zap_pte_range
                add_mm_rss_vec
                   add_mm_counter                    -> decrease the 
mm_counter
       tlb_finish_mmu
         arch_tlb_finish_mmu
           tlb_flush_mmu_free
             free_pages_and_swap_cache
               release_pages
                 folio_put_testzero(page)            -> not zero, skip
                   continue;
                 __folio_put_large
                   free_transhuge_page
                     free_compound_page
                       mem_cgroup_uncharge
                         page_counter_uncharge        -> decrease the 
page_counter

node_page_stat which shows in meminfo was also decreased. the 
__split_huge_pmd
seems free no physical memory unless the total THP was free.I am 
confused which
one is the true physical memory used of a process.


Kind regards,

Yongqiang Liu

Re: [QUESTION] memcg page_counter seems broken in MADV_DONTNEED with THP enabled

[Yang Shi]

On Sat, Nov 26, 2022 at 5:10 AM Yongqiang Liu <liuyongqiang13@huawei.com> wrote:
>
> Hi,
>
> We use mm_counter to how much a process physical memory used. Meanwhile,
> page_counter of a memcg is used to count how much a cgroup physical
> memory used.
> If a cgroup only contains a process, they looks almost the same. But with
> THP enabled, sometimes memory.usage_in_bytes in memcg may be twice or
> more than rss
> in proc/[pid]/smaps_rollup as follow:
>
> [root@localhost sda]# cat /sys/fs/cgroup/memory/test/memory.usage_in_bytes
> 1080930304
> [root@localhost sda]# cat /sys/fs/cgroup/memory/test/cgroup.procs
> 1290
> [root@localhost sda]# cat /proc/1290/smaps_rollup
> 55ba80600000-ffffffffff601000 ---p 00000000 00:00 0
> [rollup]
> Rss:              500648 kB
> Pss:              498337 kB
> Shared_Clean:       2732 kB
> Shared_Dirty:          0 kB
> Private_Clean:       364 kB
> Private_Dirty:    497552 kB
> Referenced:       500648 kB
> Anonymous:        492016 kB
> LazyFree:              0 kB
> AnonHugePages:    129024 kB
> ShmemPmdMapped:        0 kB
> Shared_Hugetlb:        0 kB
> Private_Hugetlb:       0 kB
> Swap:                  0 kB
> SwapPss:               0 kB
> Locked:                0 kB
> THPeligible:    0
>
> I have found the differences was because that __split_huge_pmd decrease
> the mm_counter but page_counter in memcg was not decreased with refcount
> of a head page is not zero. Here are the follows:
>
> do_madvise
>    madvise_dontneed_free
>      zap_page_range
>        unmap_single_vma
>          zap_pud_range
>            zap_pmd_range
>              __split_huge_pmd
>                __split_huge_pmd_locked
>                  __mod_lruvec_page_state
>              zap_pte_range
>                 add_mm_rss_vec
>                    add_mm_counter                    -> decrease the
> mm_counter
>        tlb_finish_mmu
>          arch_tlb_finish_mmu
>            tlb_flush_mmu_free
>              free_pages_and_swap_cache
>                release_pages
>                  folio_put_testzero(page)            -> not zero, skip
>                    continue;
>                  __folio_put_large
>                    free_transhuge_page
>                      free_compound_page
>                        mem_cgroup_uncharge
>                          page_counter_uncharge        -> decrease the
> page_counter
>
> node_page_stat which shows in meminfo was also decreased. the
> __split_huge_pmd
> seems free no physical memory unless the total THP was free.I am
> confused which
> one is the true physical memory used of a process.

This should be caused by the deferred split of THP. When MADV_DONTNEED
is called on the partial of the map, the huge PMD is split, but the
THP itself will not be split until the memory pressure is hit (global
or memcg limit). So the unmapped sub pages are actually not freed
until that point. So the mm counter is decreased due to the zapping
but the physical pages are not actually freed then uncharged from
memcg.

>
>
> Kind regards,
>
> Yongqiang Liu
>
>

Re: [QUESTION] memcg page_counter seems broken in MADV_DONTNEED with THP enabled

[Michal Hocko]

On Mon 28-11-22 12:01:37, Yang Shi wrote:
> On Sat, Nov 26, 2022 at 5:10 AM Yongqiang Liu <liuyongqiang13@huawei.com> wrote:
> >
> > Hi,
> >
> > We use mm_counter to how much a process physical memory used. Meanwhile,
> > page_counter of a memcg is used to count how much a cgroup physical
> > memory used.
> > If a cgroup only contains a process, they looks almost the same. But with
> > THP enabled, sometimes memory.usage_in_bytes in memcg may be twice or
> > more than rss
> > in proc/[pid]/smaps_rollup as follow:
[...]
> > node_page_stat which shows in meminfo was also decreased. the
> > __split_huge_pmd
> > seems free no physical memory unless the total THP was free.I am
> > confused which
> > one is the true physical memory used of a process.
> 
> This should be caused by the deferred split of THP. When MADV_DONTNEED
> is called on the partial of the map, the huge PMD is split, but the
> THP itself will not be split until the memory pressure is hit (global
> or memcg limit). So the unmapped sub pages are actually not freed
> until that point. So the mm counter is decreased due to the zapping
> but the physical pages are not actually freed then uncharged from
> memcg.

Yes, and this is not really bound to THP. Consider a page cache. It can
be accessed via syscalls when it doesn't correspondent to rss at all
while it is still charged to a memcg. Or it can be mapped and then later
unmapped so it disappear from rss while it is still charged until it
gets reclaimed by the memory pressure. Or it can be an in-memory object
that is not bound to any process life time (e.g. tmpfs). Or it can be a
kernel memory charged to a memcg which is not covered by rss because it
is either not mapped or it is unknown to rss counters.
-- 
Michal Hocko
SUSE Labs

Re: [QUESTION] memcg page_counter seems broken in MADV_DONTNEED with THP enabled

[Yongqiang Liu]

在 2022/11/29 16:10, Michal Hocko 写道:
> On Mon 28-11-22 12:01:37, Yang Shi wrote:
>> On Sat, Nov 26, 2022 at 5:10 AM Yongqiang Liu <liuyongqiang13@huawei.com> wrote:
>>> Hi,
>>>
>>> We use mm_counter to how much a process physical memory used. Meanwhile,
>>> page_counter of a memcg is used to count how much a cgroup physical
>>> memory used.
>>> If a cgroup only contains a process, they looks almost the same. But with
>>> THP enabled, sometimes memory.usage_in_bytes in memcg may be twice or
>>> more than rss
>>> in proc/[pid]/smaps_rollup as follow:
> [...]
>>> node_page_stat which shows in meminfo was also decreased. the
>>> __split_huge_pmd
>>> seems free no physical memory unless the total THP was free.I am
>>> confused which
>>> one is the true physical memory used of a process.
>> This should be caused by the deferred split of THP. When MADV_DONTNEED
>> is called on the partial of the map, the huge PMD is split, but the
>> THP itself will not be split until the memory pressure is hit (global
>> or memcg limit). So the unmapped sub pages are actually not freed
>> until that point. So the mm counter is decreased due to the zapping
>> but the physical pages are not actually freed then uncharged from
>> memcg.
> Yes, and this is not really bound to THP. Consider a page cache. It can
> be accessed via syscalls when it doesn't correspondent to rss at all
> while it is still charged to a memcg. Or it can be mapped and then later
> unmapped so it disappear from rss while it is still charged until it
> gets reclaimed by the memory pressure. Or it can be an in-memory object
> that is not bound to any process life time (e.g. tmpfs). Or it can be a
> kernel memory charged to a memcg which is not covered by rss because it
> is either not mapped or it is unknown to rss counters.
Thanks ! it's very nice to me.

Re: [QUESTION] memcg page_counter seems broken in MADV_DONTNEED with THP enabled

[Yang Shi]

On Tue, Nov 29, 2022 at 12:10 AM Michal Hocko <mhocko@suse.com> wrote:
>
> On Mon 28-11-22 12:01:37, Yang Shi wrote:
> > On Sat, Nov 26, 2022 at 5:10 AM Yongqiang Liu <liuyongqiang13@huawei.com> wrote:
> > >
> > > Hi,
> > >
> > > We use mm_counter to how much a process physical memory used. Meanwhile,
> > > page_counter of a memcg is used to count how much a cgroup physical
> > > memory used.
> > > If a cgroup only contains a process, they looks almost the same. But with
> > > THP enabled, sometimes memory.usage_in_bytes in memcg may be twice or
> > > more than rss
> > > in proc/[pid]/smaps_rollup as follow:
> [...]
> > > node_page_stat which shows in meminfo was also decreased. the
> > > __split_huge_pmd
> > > seems free no physical memory unless the total THP was free.I am
> > > confused which
> > > one is the true physical memory used of a process.
> >
> > This should be caused by the deferred split of THP. When MADV_DONTNEED
> > is called on the partial of the map, the huge PMD is split, but the
> > THP itself will not be split until the memory pressure is hit (global
> > or memcg limit). So the unmapped sub pages are actually not freed
> > until that point. So the mm counter is decreased due to the zapping
> > but the physical pages are not actually freed then uncharged from
> > memcg.
>
> Yes, and this is not really bound to THP. Consider a page cache. It can
> be accessed via syscalls when it doesn't correspondent to rss at all
> while it is still charged to a memcg. Or it can be mapped and then later
> unmapped so it disappear from rss while it is still charged until it
> gets reclaimed by the memory pressure. Or it can be an in-memory object
> that is not bound to any process life time (e.g. tmpfs). Or it can be a
> kernel memory charged to a memcg which is not covered by rss because it
> is either not mapped or it is unknown to rss counters.

Yes, good points. Thanks, Michal. And one more thing worth mentioning
is that the RSS shown by ps or smaps is different from the RSS shown
by memcg.

> --
> Michal Hocko
> SUSE Labs

Re: [QUESTION] memcg page_counter seems broken in MADV_DONTNEED with THP enabled

[Yongqiang Liu]

在 2022/11/29 4:01, Yang Shi 写道:
> On Sat, Nov 26, 2022 at 5:10 AM Yongqiang Liu <liuyongqiang13@huawei.com> wrote:
>> Hi,
>>
>> We use mm_counter to how much a process physical memory used. Meanwhile,
>> page_counter of a memcg is used to count how much a cgroup physical
>> memory used.
>> If a cgroup only contains a process, they looks almost the same. But with
>> THP enabled, sometimes memory.usage_in_bytes in memcg may be twice or
>> more than rss
>> in proc/[pid]/smaps_rollup as follow:
>>
>> [root@localhost sda]# cat /sys/fs/cgroup/memory/test/memory.usage_in_bytes
>> 1080930304
>> [root@localhost sda]# cat /sys/fs/cgroup/memory/test/cgroup.procs
>> 1290
>> [root@localhost sda]# cat /proc/1290/smaps_rollup
>> 55ba80600000-ffffffffff601000 ---p 00000000 00:00 0
>> [rollup]
>> Rss:              500648 kB
>> Pss:              498337 kB
>> Shared_Clean:       2732 kB
>> Shared_Dirty:          0 kB
>> Private_Clean:       364 kB
>> Private_Dirty:    497552 kB
>> Referenced:       500648 kB
>> Anonymous:        492016 kB
>> LazyFree:              0 kB
>> AnonHugePages:    129024 kB
>> ShmemPmdMapped:        0 kB
>> Shared_Hugetlb:        0 kB
>> Private_Hugetlb:       0 kB
>> Swap:                  0 kB
>> SwapPss:               0 kB
>> Locked:                0 kB
>> THPeligible:    0
>>
>> I have found the differences was because that __split_huge_pmd decrease
>> the mm_counter but page_counter in memcg was not decreased with refcount
>> of a head page is not zero. Here are the follows:
>>
>> do_madvise
>>     madvise_dontneed_free
>>       zap_page_range
>>         unmap_single_vma
>>           zap_pud_range
>>             zap_pmd_range
>>               __split_huge_pmd
>>                 __split_huge_pmd_locked
>>                   __mod_lruvec_page_state
>>               zap_pte_range
>>                  add_mm_rss_vec
>>                     add_mm_counter                    -> decrease the
>> mm_counter
>>         tlb_finish_mmu
>>           arch_tlb_finish_mmu
>>             tlb_flush_mmu_free
>>               free_pages_and_swap_cache
>>                 release_pages
>>                   folio_put_testzero(page)            -> not zero, skip
>>                     continue;
>>                   __folio_put_large
>>                     free_transhuge_page
>>                       free_compound_page
>>                         mem_cgroup_uncharge
>>                           page_counter_uncharge        -> decrease the
>> page_counter
>>
>> node_page_stat which shows in meminfo was also decreased. the
>> __split_huge_pmd
>> seems free no physical memory unless the total THP was free.I am
>> confused which
>> one is the true physical memory used of a process.
> This should be caused by the deferred split of THP. When MADV_DONTNEED
> is called on the partial of the map, the huge PMD is split, but the
> THP itself will not be split until the memory pressure is hit (global
> or memcg limit). So the unmapped sub pages are actually not freed
> until that point. So the mm counter is decreased due to the zapping
> but the physical pages are not actually freed then uncharged from
> memcg.

Thanks!

I don't know how much memory a real workload will cost.So I just

test the max_usage_in_bytes of memcg with THP disabled and add a little bit

more for the limit_in_byte of memcg with THP enabled which trigger a oom...

(actually it costed 100M more with THP enabled). Another testcase which I

known the amout of memory will cost don't trigger a oom with suitable

memcg limit  and I see the THP split when the memory hit the limit.


I have another concern that k8s usually use (rss - files) to estimate

the memory workload but the anon_thp in the defered list charged

in memcg will make it look higher than actucal. And it seems the

container will be killed without oom...

Is it suitable to add meminfo of a deferred split list of THP?

>>
>> Kind regards,
>>
>> Yongqiang Liu
>>
>>
> .

Re: [QUESTION] memcg page_counter seems broken in MADV_DONTNEED with THP enabled

[Yang Shi]

On Tue, Nov 29, 2022 at 5:14 AM Yongqiang Liu <liuyongqiang13@huawei.com> wrote:
>
>
> 在 2022/11/29 4:01, Yang Shi 写道:
> > On Sat, Nov 26, 2022 at 5:10 AM Yongqiang Liu <liuyongqiang13@huawei.com> wrote:
> >> Hi,
> >>
> >> We use mm_counter to how much a process physical memory used. Meanwhile,
> >> page_counter of a memcg is used to count how much a cgroup physical
> >> memory used.
> >> If a cgroup only contains a process, they looks almost the same. But with
> >> THP enabled, sometimes memory.usage_in_bytes in memcg may be twice or
> >> more than rss
> >> in proc/[pid]/smaps_rollup as follow:
> >>
> >> [root@localhost sda]# cat /sys/fs/cgroup/memory/test/memory.usage_in_bytes
> >> 1080930304
> >> [root@localhost sda]# cat /sys/fs/cgroup/memory/test/cgroup.procs
> >> 1290
> >> [root@localhost sda]# cat /proc/1290/smaps_rollup
> >> 55ba80600000-ffffffffff601000 ---p 00000000 00:00 0
> >> [rollup]
> >> Rss:              500648 kB
> >> Pss:              498337 kB
> >> Shared_Clean:       2732 kB
> >> Shared_Dirty:          0 kB
> >> Private_Clean:       364 kB
> >> Private_Dirty:    497552 kB
> >> Referenced:       500648 kB
> >> Anonymous:        492016 kB
> >> LazyFree:              0 kB
> >> AnonHugePages:    129024 kB
> >> ShmemPmdMapped:        0 kB
> >> Shared_Hugetlb:        0 kB
> >> Private_Hugetlb:       0 kB
> >> Swap:                  0 kB
> >> SwapPss:               0 kB
> >> Locked:                0 kB
> >> THPeligible:    0
> >>
> >> I have found the differences was because that __split_huge_pmd decrease
> >> the mm_counter but page_counter in memcg was not decreased with refcount
> >> of a head page is not zero. Here are the follows:
> >>
> >> do_madvise
> >>     madvise_dontneed_free
> >>       zap_page_range
> >>         unmap_single_vma
> >>           zap_pud_range
> >>             zap_pmd_range
> >>               __split_huge_pmd
> >>                 __split_huge_pmd_locked
> >>                   __mod_lruvec_page_state
> >>               zap_pte_range
> >>                  add_mm_rss_vec
> >>                     add_mm_counter                    -> decrease the
> >> mm_counter
> >>         tlb_finish_mmu
> >>           arch_tlb_finish_mmu
> >>             tlb_flush_mmu_free
> >>               free_pages_and_swap_cache
> >>                 release_pages
> >>                   folio_put_testzero(page)            -> not zero, skip
> >>                     continue;
> >>                   __folio_put_large
> >>                     free_transhuge_page
> >>                       free_compound_page
> >>                         mem_cgroup_uncharge
> >>                           page_counter_uncharge        -> decrease the
> >> page_counter
> >>
> >> node_page_stat which shows in meminfo was also decreased. the
> >> __split_huge_pmd
> >> seems free no physical memory unless the total THP was free.I am
> >> confused which
> >> one is the true physical memory used of a process.
> > This should be caused by the deferred split of THP. When MADV_DONTNEED
> > is called on the partial of the map, the huge PMD is split, but the
> > THP itself will not be split until the memory pressure is hit (global
> > or memcg limit). So the unmapped sub pages are actually not freed
> > until that point. So the mm counter is decreased due to the zapping
> > but the physical pages are not actually freed then uncharged from
> > memcg.
>
> Thanks!
>
> I don't know how much memory a real workload will cost.So I just
>
> test the max_usage_in_bytes of memcg with THP disabled and add a little bit
>
> more for the limit_in_byte of memcg with THP enabled which trigger a oom...
>
> (actually it costed 100M more with THP enabled). Another testcase which I
>
> known the amout of memory will cost don't trigger a oom with suitable
>
> memcg limit  and I see the THP split when the memory hit the limit.
>
>
> I have another concern that k8s usually use (rss - files) to estimate

Do you mean "workingset" used by some 3rd party k8s monitoring tools?
I recall that depends on what monitoring tools you use, for example,
some monitoring use active_anon + active_file.

>
> the memory workload but the anon_thp in the defered list charged
>
> in memcg will make it look higher than actucal. And it seems the

Yes, but the deferred split shrinker should handle this quite gracefully.

>
> container will be killed without oom...

If you have some userspace daemons which monitor the memory usage by
rss, and try to behave smarter to kill the container by looking at rss
solely, you may kill the container prematurely.

>
> Is it suitable to add meminfo of a deferred split list of THP?

We could, but I don't think of how it will be used to improve the
usecase. Any more thoughts?

>
> >>
> >> Kind regards,
> >>
> >> Yongqiang Liu
> >>
> >>
> > .

Re: [QUESTION] memcg page_counter seems broken in MADV_DONTNEED with THP enabled

[Yongqiang Liu]

在 2022/11/30 1:23, Yang Shi 写道:
> On Tue, Nov 29, 2022 at 5:14 AM Yongqiang Liu <liuyongqiang13@huawei.com> wrote:
>>
>> 在 2022/11/29 4:01, Yang Shi 写道:
>>> On Sat, Nov 26, 2022 at 5:10 AM Yongqiang Liu <liuyongqiang13@huawei.com> wrote:
>>>> Hi,
>>>>
>>>> We use mm_counter to how much a process physical memory used. Meanwhile,
>>>> page_counter of a memcg is used to count how much a cgroup physical
>>>> memory used.
>>>> If a cgroup only contains a process, they looks almost the same. But with
>>>> THP enabled, sometimes memory.usage_in_bytes in memcg may be twice or
>>>> more than rss
>>>> in proc/[pid]/smaps_rollup as follow:
>>>>
>>>> [root@localhost sda]# cat /sys/fs/cgroup/memory/test/memory.usage_in_bytes
>>>> 1080930304
>>>> [root@localhost sda]# cat /sys/fs/cgroup/memory/test/cgroup.procs
>>>> 1290
>>>> [root@localhost sda]# cat /proc/1290/smaps_rollup
>>>> 55ba80600000-ffffffffff601000 ---p 00000000 00:00 0
>>>> [rollup]
>>>> Rss:              500648 kB
>>>> Pss:              498337 kB
>>>> Shared_Clean:       2732 kB
>>>> Shared_Dirty:          0 kB
>>>> Private_Clean:       364 kB
>>>> Private_Dirty:    497552 kB
>>>> Referenced:       500648 kB
>>>> Anonymous:        492016 kB
>>>> LazyFree:              0 kB
>>>> AnonHugePages:    129024 kB
>>>> ShmemPmdMapped:        0 kB
>>>> Shared_Hugetlb:        0 kB
>>>> Private_Hugetlb:       0 kB
>>>> Swap:                  0 kB
>>>> SwapPss:               0 kB
>>>> Locked:                0 kB
>>>> THPeligible:    0
>>>>
>>>> I have found the differences was because that __split_huge_pmd decrease
>>>> the mm_counter but page_counter in memcg was not decreased with refcount
>>>> of a head page is not zero. Here are the follows:
>>>>
>>>> do_madvise
>>>>      madvise_dontneed_free
>>>>        zap_page_range
>>>>          unmap_single_vma
>>>>            zap_pud_range
>>>>              zap_pmd_range
>>>>                __split_huge_pmd
>>>>                  __split_huge_pmd_locked
>>>>                    __mod_lruvec_page_state
>>>>                zap_pte_range
>>>>                   add_mm_rss_vec
>>>>                      add_mm_counter                    -> decrease the
>>>> mm_counter
>>>>          tlb_finish_mmu
>>>>            arch_tlb_finish_mmu
>>>>              tlb_flush_mmu_free
>>>>                free_pages_and_swap_cache
>>>>                  release_pages
>>>>                    folio_put_testzero(page)            -> not zero, skip
>>>>                      continue;
>>>>                    __folio_put_large
>>>>                      free_transhuge_page
>>>>                        free_compound_page
>>>>                          mem_cgroup_uncharge
>>>>                            page_counter_uncharge        -> decrease the
>>>> page_counter
>>>>
>>>> node_page_stat which shows in meminfo was also decreased. the
>>>> __split_huge_pmd
>>>> seems free no physical memory unless the total THP was free.I am
>>>> confused which
>>>> one is the true physical memory used of a process.
>>> This should be caused by the deferred split of THP. When MADV_DONTNEED
>>> is called on the partial of the map, the huge PMD is split, but the
>>> THP itself will not be split until the memory pressure is hit (global
>>> or memcg limit). So the unmapped sub pages are actually not freed
>>> until that point. So the mm counter is decreased due to the zapping
>>> but the physical pages are not actually freed then uncharged from
>>> memcg.
>> Thanks!
>>
>> I don't know how much memory a real workload will cost.So I just
>>
>> test the max_usage_in_bytes of memcg with THP disabled and add a little bit
>>
>> more for the limit_in_byte of memcg with THP enabled which trigger a oom...
>>
>> (actually it costed 100M more with THP enabled). Another testcase which I
>>
>> known the amout of memory will cost don't trigger a oom with suitable
>>
>> memcg limit  and I see the THP split when the memory hit the limit.
>>
>>
>> I have another concern that k8s usually use (rss - files) to estimate
> Do you mean "workingset" used by some 3rd party k8s monitoring tools?
> I recall that depends on what monitoring tools you use, for example,
> some monitoring use active_anon + active_file.

Yes, I notice the k8s use a parent pod which set a memcg limit to cover all

child pods, and workingset monitor is watch the root memcg.

>
>> the memory workload but the anon_thp in the defered list charged
>>
>> in memcg will make it look higher than actucal. And it seems the
> Yes, but the deferred split shrinker should handle this quite gracefully.
>
>> container will be killed without oom...
> If you have some userspace daemons which monitor the memory usage by
> rss, and try to behave smarter to kill the container by looking at rss
> solely, you may kill the container prematurely.
Thanks.
>
>> Is it suitable to add meminfo of a deferred split list of THP?
> We could, but I don't think of how it will be used to improve the
> usecase. Any more thoughts?

In current k8s scenario, I think it will not kill the container with the 
parent

pod memcg limit set correctly.

Maybe  the meminfo with a split interface  will be helpful for user to

release memory in advance.

>>>> Kind regards,
>>>>
>>>> Yongqiang Liu
>>>>
>>>>
>>> .
> .