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

Baolin Wang
2024-07-01T08:33:49Z

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)