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From: David Hildenbrand <david@redhat.com>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org,
	linux-arch@vger.kernel.org, Will Deacon <will@kernel.org>,
	Dave P Martin <Dave.Martin@arm.com>,
	Vincenzo Frascino <vincenzo.frascino@arm.com>,
	Szabolcs Nagy <szabolcs.nagy@arm.com>,
	Kevin Brodsky <kevin.brodsky@arm.com>,
	Andrey Konovalov <andreyknvl@google.com>,
	Peter Collingbourne <pcc@google.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Steven Price <steven.price@arm.com>
Subject: Re: [PATCH v6 06/26] mm: Add PG_arch_2 page flag
Date: Mon, 6 Jul 2020 14:42:59 +0200	[thread overview]
Message-ID: <2f77487a-e92e-1a38-ffd9-e5506441d25d@redhat.com> (raw)
Message-ID: <20200706124259.Q1_UyQ41_CRUxV5TX8inWeMXSkIclHxw_1foGuEonSk@z> (raw)
In-Reply-To: <20200706112057.GA6432@gaia>

On 06.07.20 13:21, Catalin Marinas wrote:
> On Mon, Jul 06, 2020 at 10:24:04AM +0200, David Hildenbrand wrote:
>> On 03.07.20 17:36, Catalin Marinas wrote:
>>> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
>>> index 6be1aa559b1e..276140c94f4a 100644
>>> --- a/include/linux/page-flags.h
>>> +++ b/include/linux/page-flags.h
>>> @@ -135,6 +135,9 @@ enum pageflags {
>>>  #if defined(CONFIG_IDLE_PAGE_TRACKING) && defined(CONFIG_64BIT)
>>>  	PG_young,
>>>  	PG_idle,
>>> +#endif
>>> +#ifdef CONFIG_64BIT
>>> +	PG_arch_2,
>>>  #endif
>>>  	__NR_PAGEFLAGS,
>>
>> People are usually *very* picky when it comes to new page flags. It
>> somewhat concerns me that we bump up __NR_PAGEFLAGS for any 64bit arch.
>> That feels wrong.
> 
> It was guarded by a specific config option initially but the comments
> suggested that it could be dropped for 64-bit architectures:
> 
> https://lore.kernel.org/linux-arm-kernel/20200624113307.6165b3db2404c9d37b870a90@linux-foundation.org/
> 
> The page flags is indeed a pretty limited resource as it also includes
> the sparsemem section, node and zone fields. However, on 64-bit this
> should be fine (the sparsemem section is gone with vmemmap support).

Right, so 64bit architectures/configs with SPARSEMEM &&
!SPARSEMEM_VMEMMAP could be affected only. I think mips would be one
example where we don't have VMEMMAP support. For most other 64bit
architectures (x86_64, s390x, powerpc, ...) SPARSEMEM_VMEMMAP should be
the default (although I've seen bug reports/configs where VMEMMAP was
disabled).

-- 
Thanks,

David / dhildenb

  reply	other threads:[~2020-07-06 12:42 UTC|newest]

Thread overview: 43+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-03 15:36 [PATCH v6 00/26] arm64: Memory Tagging Extension user-space support Catalin Marinas
2020-07-03 15:36 ` Catalin Marinas
2020-07-03 15:36 ` [PATCH v6 01/26] arm64: mte: system register definitions Catalin Marinas
2020-07-03 15:36 ` [PATCH v6 02/26] arm64: mte: CPU feature detection and initial sysreg configuration Catalin Marinas
2020-07-13 10:08   ` Steven Price
2020-07-13 17:45     ` Catalin Marinas
2020-07-03 15:36 ` [PATCH v6 03/26] arm64: mte: Use Normal Tagged attributes for the linear map Catalin Marinas
2020-07-03 15:36 ` [PATCH v6 04/26] arm64: mte: Add specific SIGSEGV codes Catalin Marinas
2020-07-03 15:36 ` [PATCH v6 05/26] arm64: mte: Handle synchronous and asynchronous tag check faults Catalin Marinas
2020-07-03 15:36 ` [PATCH v6 06/26] mm: Add PG_arch_2 page flag Catalin Marinas
2020-07-06  8:24   ` David Hildenbrand
2020-07-06  8:24     ` David Hildenbrand
2020-07-06 11:21     ` Catalin Marinas
2020-07-06 12:42       ` David Hildenbrand [this message]
2020-07-06 12:42         ` David Hildenbrand
2020-07-03 15:36 ` [PATCH v6 07/26] mm: Preserve the PG_arch_* flags in __split_huge_page_tail() Catalin Marinas
2020-07-06 14:16   ` David Hildenbrand
2020-07-06 14:16     ` David Hildenbrand
2020-07-06 16:30     ` Catalin Marinas
2020-07-06 17:56       ` David Hildenbrand
2020-07-08 12:17         ` Catalin Marinas
2020-07-03 15:37 ` [PATCH v6 08/26] arm64: mte: Clear the tags when a page is mapped in user-space with PROT_MTE Catalin Marinas
2020-07-03 15:37 ` [PATCH v6 09/26] arm64: mte: Tags-aware copy_{user_,}highpage() implementations Catalin Marinas
2020-07-03 15:37 ` [PATCH v6 10/26] arm64: Avoid unnecessary clear_user_page() indirection Catalin Marinas
2020-07-03 15:37 ` [PATCH v6 11/26] arm64: mte: Tags-aware aware memcmp_pages() implementation Catalin Marinas
2020-07-03 15:37 ` [PATCH v6 12/26] mm: Introduce arch_calc_vm_flag_bits() Catalin Marinas
2020-07-03 15:37 ` [PATCH v6 13/26] arm64: mte: Add PROT_MTE support to mmap() and mprotect() Catalin Marinas
2020-07-03 15:37 ` [PATCH v6 14/26] mm: Introduce arch_validate_flags() Catalin Marinas
2020-07-03 15:37 ` [PATCH v6 15/26] arm64: mte: Validate the PROT_MTE request via arch_validate_flags() Catalin Marinas
2020-07-03 15:37 ` [PATCH v6 16/26] mm: Allow arm64 mmap(PROT_MTE) on RAM-based files Catalin Marinas
2020-07-03 15:37 ` [PATCH v6 17/26] arm64: mte: Allow user control of the tag check mode via prctl() Catalin Marinas
2020-07-03 15:37 ` [PATCH v6 18/26] arm64: mte: Allow user control of the generated random tags " Catalin Marinas
2020-07-03 15:37 ` [PATCH v6 19/26] arm64: mte: Restore the GCR_EL1 register after a suspend Catalin Marinas
2020-07-03 15:37 ` [PATCH v6 20/26] arm64: mte: Add PTRACE_{PEEK,POKE}MTETAGS support Catalin Marinas
2020-07-09 14:41   ` Luis Machado
2020-07-03 15:37 ` [PATCH v6 21/26] fs: Handle intra-page faults in copy_mount_options() Catalin Marinas
2020-07-03 15:37 ` [PATCH v6 22/26] mm: Add arch hooks for saving/restoring tags Catalin Marinas
2020-07-03 15:37 ` [PATCH v6 23/26] arm64: mte: Enable swap of tagged pages Catalin Marinas
2020-07-03 15:37 ` [PATCH v6 24/26] arm64: mte: Save tags when hibernating Catalin Marinas
2020-07-03 15:37 ` [PATCH v6 25/26] arm64: mte: Kconfig entry Catalin Marinas
2020-07-03 15:37 ` [PATCH v6 26/26] arm64: mte: Add Memory Tagging Extension documentation Catalin Marinas
2020-07-09  9:32   ` Szabolcs Nagy
2020-07-09 14:43     ` Catalin Marinas

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