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From: Yang Shi <>
To: Michal Hocko <>
Subject: Re: [RFC v2 PATCH] mm: shmem: make stat.st_blksize return huge page size if THP is on
Date: Tue, 24 Apr 2018 07:08:36 -0600	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On 4/24/18 6:43 AM, Michal Hocko wrote:
> On Mon 23-04-18 21:41:50, Yang Shi wrote:
>> On 4/23/18 9:04 AM, Michal Hocko wrote:
>>> On Sun 22-04-18 21:28:59, Yang Shi wrote:
>>>> On 4/22/18 6:47 PM, Michal Hocko wrote:
>>> [...]
>>>>> will be used on the first aligned address even when the initial/last
>>>>> portion of the mapping is not THP aligned.
>>>> No, my test shows it is not. And, transhuge_vma_suitable() does check the
>>>> virtual address alignment. If it is not huge page size aligned, it will not
>>>> set PMD for huge page.
>>> It's been quite some time since I've looked at that code but I think you
>>> are wrong. It just doesn't make sense to make the THP decision on the
>>> VMA alignment much. Kirill, can you clarify please?
>> Thanks a lot Michal and Kirill to elaborate how tmpfs THP make pmd map.
>> I did a quick test, THP will be PMD mapped as long as :
>> * hint address is huge page aligned if MAP_FIXED
>> Or
>> * offset is huge page aligned
>> And
>> * The size is big enough (>= huge page size)
>> This test does verify what Kirill said. And, I dig into a little further
>> qemu code and did strace, qemu does try to mmap the file to non huge page
>> aligned address with MAP_FIXED.
> Does it make sense to contact Qemu developers and probably fix this?

Yes, I think so. We can submit a bug report to QEMU.


      reply	other threads:[~2018-04-24 13:08 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-20 16:33 [RFC v2 PATCH] mm: shmem: make stat.st_blksize return huge page size if THP is on Yang Shi
2018-04-23  0:47 ` Michal Hocko
2018-04-23  3:28   ` Yang Shi
2018-04-23 15:04     ` Michal Hocko
2018-04-23 16:19       ` Yang Shi
2018-04-24  3:41       ` Yang Shi
2018-04-24 12:43         ` Michal Hocko
2018-04-24 13:08           ` Yang Shi [this message]

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