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

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Date: Mon, 01 Jul 2024 16:24:22 +0800
From: "Bang Li" <libang.li@...group.com>
To: David Hildenbrand <david@...hat.com>, hughd@...gle.com,
 akpm@...ux-foundation.org
Cc: ryan.roberts@....com, wangkefeng.wang@...wei.com,
 baolin.wang@...ux.alibaba.com, ziy@...dia.com, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org
Subject: Re: [PATCH] support "THPeligible" semantics for mTHP with anonymous
 shmem

Hi David,

Thanks for you review!

On 2024/7/1 14:57, David Hildenbrand wrote:
> On 28.06.24 12:49, 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@...group.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);
> 
> I would have thought the correct fix is to return the correct result 
> from thp_vma_allowable_orders().
> 

Agreed. I'll try to reimplement this in thp_vma_allowable_orders().

Thanks again for the review!
Bang