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From: Christophe Leroy <christophe.leroy@csgroup.eu>
To: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
	Matthew Wilcox <willy@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	Nick Piggin <npiggin@gmail.com>, Linux-MM <linux-mm@kvack.org>,
	Kalesh Singh <kaleshsingh@google.com>,
	Joel Fernandes <joel@joelfernandes.org>,
	"Kirill A . Shutemov" <kirill@shutemov.name>,
	Andrew Morton <akpm@linux-foundation.org>,
	linuxppc-dev <linuxppc-dev@lists.ozlabs.org>
Subject: Re: [PATCH 5/6] mm/mremap: Use pmd/pud_poplulate to update page table entries
Date: Mon, 14 Jun 2021 07:27:19 +0200	[thread overview]
Message-ID: <d49125f2-ab15-05a8-7982-12cbbfcc4dc9@csgroup.eu> (raw)
In-Reply-To: <dd2f0d9d-da78-46a4-78cb-c5cfb7df7f16@linux.ibm.com>



Le 13/06/2021 à 13:13, Aneesh Kumar K.V a écrit :
> On 6/13/21 4:20 PM, Matthew Wilcox wrote:
>> On Sun, Jun 13, 2021 at 02:36:13PM +0530, Aneesh Kumar K.V wrote:
>>> IIUC the reason why we do have pmd_pgtable() is that pgtable_t type
>>> is arch dependent. On some architecture it is pte_t * and on the other
>>> struct page *. The reason being highmem and level 4 page table can
>>> be located in highmem.
>>
>> That is ahistorical.  See 2f569afd9ced9ebec9a6eb3dbf6f83429be0a7b4 --
>> we have pgtable_t for the benefit of s390's crazy sub-page page table
>> sizes.
> 
> That is also true with ppc64. We do sub-page page table size. I was trying to explain why it can't 
> be pte_t * everywhere and why we have
> it as struct page *.

ppc32 as well. On the 8xx, with 16k size pages, the HW still use 4k page tables, so we do use sub-pages.

In order too keep the code simple, we have converted all powerpc to sub-pages for that, allthough 
some powerpc platforms have only one sub-page per page.

Christophe

  reply	other threads:[~2021-06-14  5:27 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-10  8:35 [PATCH 0/6] mremap fixes Aneesh Kumar K.V
2021-06-10  8:35 ` [PATCH 1/6] selftest/mremap_test: Update the test to handle pagesize other than 4K Aneesh Kumar K.V
2021-06-10  8:35 ` [PATCH 2/6] selftest/mremap_test: Avoid crash with static build Aneesh Kumar K.V
2021-06-10  8:35 ` [PATCH 3/6] mm/mremap: Convert huge PUD move to separate helper Aneesh Kumar K.V
2021-06-10 22:03   ` Hugh Dickins
2021-06-10  8:35 ` [PATCH 4/6] mm/mremap: Don't enable optimized PUD move if page table levels is 2 Aneesh Kumar K.V
2021-06-10  8:35 ` [PATCH 5/6] mm/mremap: Use pmd/pud_poplulate to update page table entries Aneesh Kumar K.V
2021-06-10 18:16   ` Linus Torvalds
2021-06-13  9:06     ` Aneesh Kumar K.V
2021-06-13 10:50       ` Matthew Wilcox
2021-06-13 11:13         ` Aneesh Kumar K.V
2021-06-14  5:27           ` Christophe Leroy [this message]
2021-06-13 18:53       ` Linus Torvalds
2021-06-10  8:35 ` [PATCH 6/6] mm/mremap: hold the rmap lock in write mode when moving " Aneesh Kumar K.V
2021-06-11  8:11   ` Jann Horn

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