Re: [RFC 2/2] khugepaged: use upgrade_read() to optimize collapse_huge_page

lizhe.67
2024-10-17T06:18:49Z

On Wed, 16 Oct 2024 12:53:15 +0100, willy@infradead.org wrote:

>On Wed, Oct 16, 2024 at 12:36:00PM +0800, lizhe.67@bytedance.com wrote:
>> From: Li Zhe <lizhe.67@bytedance.com>
>>
>> In function collapse_huge_page(), we drop mmap read lock and get
>> mmap write lock to prevent most accesses to pagetables. There is
>> a small time window to allow other tasks to acquire the mmap lock.
>> With the use of upgrade_read(), we don't need to check vma and pmd
>> again in most cases.
>
>This is clearly a performance optimisation. So you must have some
>numebrs that justify this, please include them.

Yes, I will add the relevant data to v2 patch.

Thanks!