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From: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: linuxppc-dev <linuxppc-dev@lists.ozlabs.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>,
	Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH 5/6] mm/mremap: Use pmd/pud_poplulate to update page table entries
Date: Sun, 13 Jun 2021 16:43:50 +0530	[thread overview]
Message-ID: <dd2f0d9d-da78-46a4-78cb-c5cfb7df7f16@linux.ibm.com> (raw)
In-Reply-To: <YMXi6AZm4fPpPKrH@casper.infradead.org>

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 *.

> 
> Also, please stop numbering page tables upside down.  PTEs are first
> level, not fourth.
> 

POWER ISA do name it the other way. I also see some pages explaining 
levels the other way

https://www.bottomupcs.com/virtual_memory_linux.xhtml

whereas 
https://en.wikipedia.org/wiki/Intel_5-level_paging#/media/File:Page_Tables_(5_levels).svg

I am pretty sure I had commits that explained page table level as I did 
in this thread. I will switch to your suggestion in further discussions. 
May be the best solution is to attribute it with more details like level 
1 (pte_t *)?


-aneesh


  reply	other threads:[~2021-06-13 11:16 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 [this message]
2021-06-14  5:27           ` Christophe Leroy
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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