Message-ID: <02d7b8a2-b0d6-4713-b03e-5b22968387c3@gmail.com>
Date: Thu, 15 Aug 2024 14:17:45 +0800
From: Alex Shi <seakeel@...il.com>
To: Matthew Wilcox <willy@...radead.org>, alexs@...nel.org
Cc: Will Deacon <will@...nel.org>,
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Subject: Re: [RFC PATCH 00/18] use struct ptdesc to replace pgtable_t



On 8/15/24 1:13 AM, Matthew Wilcox wrote:
> On Tue, Jul 30, 2024 at 02:46:54PM +0800, alexs@...nel.org wrote:
>> We have struct ptdesc for page table descriptor a year ago, but it
>> has no much usages in kernel, while pgtable_t is used widely.
> 
> Hum, I thought I responded to this to point out the problem, but
> I don't see the response anywhere, so I'll try again.
> 
>> The pgtable_t is typedefed as 'pte_t *' in sparc, s390, powerpc and m68k
>> except SUN3, others archs are all same as 'struct page *'.
> 
> And there's a very good reason for that.  On s390 and powerpc (I cannot
> speak to the sparc/m68k), each page table is (potentially) smaller
> than PAGE_SIZE.  So we cannot do what your patch purports to do, as
> we would not know whether we're referring to the first or subsequent
> page tables contained within a page.
>> Maybe at some point in the distant future we'll be able to allocate
> a ptdesc per page table instead of per page allocated for use by page
> tables.  But we cannot do that yet.


Got it. Thanks a lot for the info!

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