Re: [PATCH] mm, memcg: Add memory.transparent_hugepage_disabled

teawater
2020-03-24T12:30:32Z

> 2020年3月24日 19:00，Michal Hocko <mhocko-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> 写道：
>
> On Tue 24-03-20 18:31:56, Hui Zhu wrote:
>> /sys/kernel/mm/transparent_hugepage/enabled is the only interface to
>> control if the application can use THP in system level.
>> Sometime, we would not want an application use THP even if
>> transparent_hugepage/enabled is set to "always" or "madvise" because
>> thp may need more cpu and memory resources in some cases.
>
> Could you specify that sometime by a real usecase in the memcg context
> please?

Thanks for your review.

We use thp+balloon to supply more memory flexibility for vm.
https://lore.kernel.org/linux-mm/1584893097-12317-1-git-send-email-teawater-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org/
This is another thread that I am working around thp+balloon.

Other applications are already deployed on these machines. The transparent_hugepage/enabled is set to never because they used to have a lot of THP related performance issues.
And some of them may call madvise thp with itself.

Then even if I set transparent_hugepage/enabled to madvise. These programs are still at risk of THP-related performance issues. That is why I need this cgroup thp switch.

>
>> This commit add a new interface memory.transparent_hugepage_disabled
>> in memcg.
>> When it set to 1, the application inside the cgroup cannot use THP
>> except dax.
>
> Why should this interface differ from the global semantic. How does it
> relate to the kcompactd. Your patch also doesn't seem to define this
> knob to have hierarchical semantic. Why?
>

According to my previous description, I didn’t get any need to add transparent_hugepage/enabled like interface.
That is why just add a switch.

What about add a transparent_hugepage/enabled like interface?

Thanks,
Hui

> All that being said, this patch is lacking both proper justification and
> the semantic is dubious to be honest. I have also say that I am not a
> great fan. THP semantic is overly complex already and adding more on top
> would require really strong usecase.
>
>> Signed-off-by: Hui Zhu <teawaterz-KPsoFbNs7GizrGE5bRqYAgC/G2K4zDHf@public.gmane.org>
>> ---
>> include/linux/huge_mm.h | 18 ++++++++++++++++--
>> include/linux/memcontrol.h | 2 ++
>> mm/memcontrol.c | 42 ++++++++++++++++++++++++++++++++++++++++++
>> mm/shmem.c | 4 ++++
>> 4 files changed, 64 insertions(+), 2 deletions(-)
>>
>> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
>> index 5aca3d1..fd81479 100644
>> --- a/include/linux/huge_mm.h
>> +++ b/include/linux/huge_mm.h
>> @@ -91,6 +91,16 @@ extern bool is_vma_temporary_stack(struct vm_area_struct *vma);
>>
>> extern unsigned long transparent_hugepage_flags;
>>
>> +#ifdef CONFIG_MEMCG
>> +extern bool memcg_transparent_hugepage_disabled(struct vm_area_struct *vma);
>> +#else
>> +static inline bool
>> +memcg_transparent_hugepage_disabled(struct vm_area_struct *vma)
>> +{
>> + return false;
>> +}
>> +#endif
>> +
>> /*
>> * to be used on vmas which are known to support THP.
>> * Use transparent_hugepage_enabled otherwise
>> @@ -106,8 +116,6 @@ static inline bool __transparent_hugepage_enabled(struct vm_area_struct *vma)
>> if (test_bit(MMF_DISABLE_THP, &vma->vm_mm->flags))
>> return false;
>>
>> - if (transparent_hugepage_flags & (1 << TRANSPARENT_HUGEPAGE_FLAG))
>> - return true;
>> /*
>> * For dax vmas, try to always use hugepage mappings. If the kernel does
>> * not support hugepages, fsdax mappings will fallback to PAGE_SIZE
>> @@ -117,6 +125,12 @@ static inline bool __transparent_hugepage_enabled(struct vm_area_struct *vma)
>> if (vma_is_dax(vma))
>> return true;
>>
>> + if (memcg_transparent_hugepage_disabled(vma))
>> + return false;
>> +
>> + if (transparent_hugepage_flags & (1 << TRANSPARENT_HUGEPAGE_FLAG))
>> + return true;
>> +
>> if (transparent_hugepage_flags &
>> (1 << TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG))
>> return !!(vma->vm_flags & VM_HUGEPAGE);
>> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
>> index a7a0a1a5..abc3142 100644
>> --- a/include/linux/memcontrol.h
>> +++ b/include/linux/memcontrol.h
>> @@ -320,6 +320,8 @@ struct mem_cgroup {
>>
>> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
>> struct deferred_split deferred_split_queue;
>> +
>> + bool transparent_hugepage_disabled;
>> #endif
>>
>> struct mem_cgroup_per_node *nodeinfo[0];
>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>> index 7a4bd8b..b6d91b6 100644
>> --- a/mm/memcontrol.c
>> +++ b/mm/memcontrol.c
>> @@ -5011,6 +5011,14 @@ mem_cgroup_css_alloc(struct cgroup_subsys_state *parent_css)
>> if (parent) {
>> memcg->swappiness = mem_cgroup_swappiness(parent);
>> memcg->oom_kill_disable = parent->oom_kill_disable;
>> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
>> + memcg->transparent_hugepage_disabled
>> + = parent->transparent_hugepage_disabled;
>> +#endif
>> + } else {
>> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
>> + memcg->transparent_hugepage_disabled = false;
>> +#endif
>> }
>> if (parent && parent->use_hierarchy) {
>> memcg->use_hierarchy = true;
>> @@ -6126,6 +6134,24 @@ static ssize_t memory_oom_group_write(struct kernfs_open_file *of,
>> return nbytes;
>> }
>>
>> +static u64 transparent_hugepage_disabled_read(struct cgroup_subsys_state *css,
>> + struct cftype *cft)
>> +{
>> + struct mem_cgroup *memcg = mem_cgroup_from_css(css);
>> +
>> + return memcg->transparent_hugepage_disabled;
>> +}
>> +
>> +static int transparent_hugepage_disabled_write(struct cgroup_subsys_state *css,
>> + struct cftype *cft, u64 val)
>> +{
>> + struct mem_cgroup *memcg = mem_cgroup_from_css(css);
>> +
>> + memcg->transparent_hugepage_disabled = !!val;
>> +
>> + return 0;
>> +}
>> +
>> static struct cftype memory_files[] = {
>> {
>> .name = "current",
>> @@ -6179,6 +6205,12 @@ static struct cftype memory_files[] = {
>> .seq_show = memory_oom_group_show,
>> .write = memory_oom_group_write,
>> },
>> + {
>> + .name = "transparent_hugepage_disabled",
>> + .flags = CFTYPE_NOT_ON_ROOT,
>> + .read_u64 = transparent_hugepage_disabled_read,
>> + .write_u64 = transparent_hugepage_disabled_write,
>> + },
>> { } /* terminate */
>> };
>>
>> @@ -6787,6 +6819,16 @@ void mem_cgroup_uncharge_skmem(struct mem_cgroup *memcg, unsigned int nr_pages)
>> refill_stock(memcg, nr_pages);
>> }
>>
>> +bool memcg_transparent_hugepage_disabled(struct vm_area_struct *vma)
>> +{
>> + struct mem_cgroup *memcg = get_mem_cgroup_from_mm(vma->vm_mm);
>> +
>> + if (memcg && memcg->transparent_hugepage_disabled)
>> + return true;
>> +
>> + return false;
>> +}
>> +
>> static int __init cgroup_memory(char *s)
>> {
>> char *token;
>> diff --git a/mm/shmem.c b/mm/shmem.c
>> index aad3ba7..253b63b 100644
>> --- a/mm/shmem.c
>> +++ b/mm/shmem.c
>> @@ -1810,6 +1810,10 @@ static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
>> goto alloc_nohuge;
>> if (shmem_huge == SHMEM_HUGE_DENY || sgp_huge == SGP_NOHUGE)
>> goto alloc_nohuge;
>> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
>> + if (memcg_transparent_hugepage_disabled(vma))
>> + goto alloc_nohuge;
>> +#endif
>> if (shmem_huge == SHMEM_HUGE_FORCE)
>> goto alloc_huge;
>> switch (sbinfo->huge) {
>> --
>> 2.7.4
>
> --
> Michal Hocko
> SUSE Labs