From: Michael Ellerman <mpe@ellerman•id.au>
To: LEROY Christophe <christophe.leroy2@cs-soprasteria•com>,
Florian Weimer <fweimer@redhat•com>,
"linuxppc-dev@lists•ozlabs.org" <linuxppc-dev@lists•ozlabs.org>
Cc: Peter Bergner <bergner@linux•ibm.com>
Subject: Re: Are 256K page sizes really a thing (on ppc64le in particular)?
Date: Sun, 29 Sep 2024 21:24:36 +1000 [thread overview]
Message-ID: <874j5yhfd7.fsf@mail.lhotse> (raw)
In-Reply-To: <eac7d905-b998-45c0-b3d5-c2f59bc37d69@cs-soprasteria.com>
LEROY Christophe <christophe.leroy2@cs-soprasteria•com> writes:
> Le 28/09/2024 à 18:08, Florian Weimer a écrit :
>> I'm working on adding a <sys/pagesize.h> header to glibc, so that
>> programmers can easily determine the range of possible page sizes for a
>> particular target, for things like pointer tagging and mapped file
>> alignment requirements.
>>
>> I'm not familiar from the Kconfig system, but as far as I can tell, this
>> ensures that 256 KiB pages are only available on 44x machines:
>>
>> arch/powerpc/Kconfig-config PPC_256K_PAGES
>> arch/powerpc/Kconfig- bool "256k page size (Requires non-standard binutils settings)"
>> arch/powerpc/Kconfig- depends on 44x && !PPC_47x
>> arch/powerpc/Kconfig: select HAVE_PAGE_SIZE_256KB
>>
>> And none of the 44x configurations set 64BIT, so it's all 32-bit.
>>
>> Would it still make sense to recommend 256 KiB file alignment to
>> programmers on 32-bit PowerPC, or should <sys/pagesize.h> pretend
>> that the maximum page size is 64 KiB?
>>
>
> For ppc64le it is definitely not a thing.
>
> As you noticed, 256K pages are only for 44x which is a 32 bits
> processor, and as mentioned in the CONFIG_PPC_256K_PAGES help:
>
> The kernel will only be able to run applications that have been
> compiled with '-zmax-page-size' set to 256K (the default is 64K) using
> binutils later than 2.17.50.0.3, or by patching the ELF_MAXPAGESIZE
> definition from 0x10000 to 0x40000 in older versions.
>
>
> So 256 Kbytes pages is a corner case and I think the default max
> alignment should remain 64 Kbytes.
I agree.
cheers
prev parent reply other threads:[~2024-09-29 11:24 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-09-28 16:08 Are 256K page sizes really a thing (on ppc64le in particular)? Florian Weimer
2024-09-28 16:38 ` LEROY Christophe
2024-09-29 11:24 ` Michael Ellerman [this message]
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