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From: Yang Shi <yang.shi@linux.alibaba.com>
To: Michal Hocko <mhocko@kernel.org>, kirill.shutemov@linux.intel.com
Cc: hughd@google.com, hch@infradead.org, viro@zeniv.linux.org.uk,
	akpm@linux-foundation.org, linux-fsdevel@vger.kernel.org,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC v2 PATCH] mm: shmem: make stat.st_blksize return huge page size if THP is on
Date: Mon, 23 Apr 2018 10:19:27 -0600	[thread overview]
Message-ID: <4d2693a6-e2eb-5108-d423-765de2bf7a19@linux.alibaba.com> (raw)
In-Reply-To: <20180423150435.GS17484@dhcp22.suse.cz>



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?

In the test, QEMU is trying to mmap a file (16GB in my configuration) + 
a guard page. If the page size is 4KB, there not any pages are mapped by 
PMD, but if the page size is 2MB (huge page aligned) we can see a lot 
pages are mapped by PMD. The test result is showed in the commit log.

So, if your assumption is right, there must be something wrong in THP code.

>
> Please note that I have no objections to actually export the huge page
> size as the max block size but your changelog just doesn't make any
> sense to me.

Thanks,
Yang

  reply	other threads:[~2018-04-23 16:19 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 [this message]
2018-04-24  3:41       ` Yang Shi
2018-04-24 12:43         ` Michal Hocko
2018-04-24 13:08           ` Yang Shi

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