Re: [PATCH] support "THPeligible" semantics for mTHP with anonymous shmem

[Baolin Wang <baolin.wang@linux.alibaba.com>]

On 2024/7/1 15:55, Ryan Roberts wrote:
> On 28/06/2024 11:49, Bang Li wrote:
>> After the commit 7fb1b252afb5 ("mm: shmem: add mTHP support for
>> anonymous shmem"), we can configure different policies through
>> the multi-size THP sysfs interface for anonymous shmem. But
>> currently "THPeligible" indicates only whether the mapping is
>> eligible for allocating THP-pages as well as the THP is PMD
>> mappable or not for anonymous shmem, we need to support semantics
>> for mTHP with anonymous shmem similar to those for mTHP with
>> anonymous memory.
>>
>> Signed-off-by: Bang Li <libang.li@antgroup.com>
>> ---
>>   fs/proc/task_mmu.c      | 10 +++++++---
>>   include/linux/huge_mm.h | 11 +++++++++++
>>   mm/shmem.c              |  9 +--------
>>   3 files changed, 19 insertions(+), 11 deletions(-)
>>
>> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
>> index 93fb2c61b154..09b5db356886 100644
>> --- a/fs/proc/task_mmu.c
>> +++ b/fs/proc/task_mmu.c
>> @@ -870,6 +870,7 @@ static int show_smap(struct seq_file *m, void *v)
>>   {
>>   	struct vm_area_struct *vma = v;
>>   	struct mem_size_stats mss = {};
>> +	bool thp_eligible;
>>   
>>   	smap_gather_stats(vma, &mss, 0);
>>   
>> @@ -882,9 +883,12 @@ static int show_smap(struct seq_file *m, void *v)
>>   
>>   	__show_smap(m, &mss, false);
>>   
>> -	seq_printf(m, "THPeligible:    %8u\n",
>> -		   !!thp_vma_allowable_orders(vma, vma->vm_flags,
>> -			   TVA_SMAPS | TVA_ENFORCE_SYSFS, THP_ORDERS_ALL));
>> +	thp_eligible = !!thp_vma_allowable_orders(vma, vma->vm_flags,
>> +						TVA_SMAPS | TVA_ENFORCE_SYSFS, THP_ORDERS_ALL);
>> +	if (vma_is_anon_shmem(vma))
>> +		thp_eligible = !!shmem_allowable_huge_orders(file_inode(vma->vm_file),
>> +							vma, vma->vm_pgoff, thp_eligible);
> 
> Afraid I haven't been following the shmem mTHP support work as much as I would
> have liked, but is there a reason why we need a separate function for shmem?

Since shmem_allowable_huge_orders() only uses shmem specific logic to 
determine if huge orders are allowable, there is no need to complicate 
the thp_vma_allowable_orders() function by adding more shmem related 
logic, making it more bloated. In my view, providing a dedicated helper 
shmem_allowable_huge_orders(), specifically for shmem, simplifies the logic.

IIUC, I agree with David's suggestion that the 
shmem_allowable_huge_orders() helper function could be used in 
thp_vma_allowable_orders() to support shmem mTHP. Something like:

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index c7ce28f6b7f3..9677fe6cf478 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -151,10 +151,13 @@ unsigned long __thp_vma_allowable_orders(struct 
vm_area_struct *vma,
          * Must be done before hugepage flags check since shmem has its
          * own flags.
          */
-       if (!in_pf && shmem_file(vma->vm_file))
-               return shmem_is_huge(file_inode(vma->vm_file), 
vma->vm_pgoff,
-                                    !enforce_sysfs, vma->vm_mm, vm_flags)
-                       ? orders : 0;
+       if (!in_pf && shmem_file(vma->vm_file)) {
+               bool global_huge = 
shmem_is_huge(file_inode(vma->vm_file), vma->vm_pgoff,
+                                    !enforce_sysfs, vma->vm_mm, vm_flags);
+
+               return shmem_allowable_huge_orders(file_inode(vma->vm_file),
+                                       vma, vma->vm_pgoff, global_huge);
+       }

         if (!vma_is_anonymous(vma)) {
                 /*

> Couldn't (shouldn't) thp_vma_allowable_orders() be taught to handle shmem too?
> 
>> +	seq_printf(m, "THPeligible:    %8u\n", thp_eligible);
>>   
>>   	if (arch_pkeys_enabled())
>>   		seq_printf(m, "ProtectionKey:  %8u\n", vma_pkey(vma));
>> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
>> index 212cca384d7e..f87136f38aa1 100644
>> --- a/include/linux/huge_mm.h
>> +++ b/include/linux/huge_mm.h
>> @@ -267,6 +267,10 @@ unsigned long thp_vma_allowable_orders(struct vm_area_struct *vma,
>>   	return __thp_vma_allowable_orders(vma, vm_flags, tva_flags, orders);
>>   }
>>   
>> +unsigned long shmem_allowable_huge_orders(struct inode *inode,
>> +				struct vm_area_struct *vma, pgoff_t index,
>> +				bool global_huge);
>> +
>>   struct thpsize {
>>   	struct kobject kobj;
>>   	struct list_head node;
>> @@ -460,6 +464,13 @@ static inline unsigned long thp_vma_allowable_orders(struct vm_area_struct *vma,
>>   	return 0;
>>   }
>>   
>> +static inline unsigned long shmem_allowable_huge_orders(struct inode *inode,
>> +				struct vm_area_struct *vma, pgoff_t index,
>> +				bool global_huge)
>> +{
>> +	return 0;
>> +}
>> +
>>   #define transparent_hugepage_flags 0UL
>>   
>>   #define thp_get_unmapped_area	NULL
>> diff --git a/mm/shmem.c b/mm/shmem.c
>> index d495c0701a83..aa85df9c662a 100644
>> --- a/mm/shmem.c
>> +++ b/mm/shmem.c
>> @@ -1622,7 +1622,7 @@ static gfp_t limit_gfp_mask(gfp_t huge_gfp, gfp_t limit_gfp)
>>   }
>>   
>>   #ifdef CONFIG_TRANSPARENT_HUGEPAGE
>> -static unsigned long shmem_allowable_huge_orders(struct inode *inode,
>> +unsigned long shmem_allowable_huge_orders(struct inode *inode,
>>   				struct vm_area_struct *vma, pgoff_t index,
>>   				bool global_huge)
>>   {
>> @@ -1707,13 +1707,6 @@ static unsigned long shmem_suitable_orders(struct inode *inode, struct vm_fault
>>   	return orders;
>>   }
>>   #else
>> -static unsigned long shmem_allowable_huge_orders(struct inode *inode,
>> -				struct vm_area_struct *vma, pgoff_t index,
>> -				bool global_huge)
>> -{
>> -	return 0;
>> -}
>> -
>>   static unsigned long shmem_suitable_orders(struct inode *inode, struct vm_fault *vmf,
>>   					   struct address_space *mapping, pgoff_t index,
>>   					   unsigned long orders)