linux-kernel - Re: [RFC V2 0/3] mm/hotplug: Pre-validate the address range with platform

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Message-ID: <7ffb5199-1b39-3f35-32cd-b59f71cc00c5@arm.com>
Date:   Wed, 2 Dec 2020 12:14:04 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     linux-mm@...ck.org, akpm@...ux-foundation.org, david@...hat.com
Cc:     linux-arm-kernel@...ts.infradead.org, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org, Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [RFC V2 0/3] mm/hotplug: Pre-validate the address range with
 platform



On 11/30/20 8:59 AM, Anshuman Khandual wrote:
> This series adds a mechanism allowing platforms to weigh in and prevalidate
> incoming address range before proceeding further with the memory hotplug.
> This helps prevent potential platform errors for the given address range,
> down the hotplug call chain, which inevitably fails the hotplug itself.
> 
> This mechanism was suggested by David Hildenbrand during another discussion
> with respect to a memory hotplug fix on arm64 platform.
> 
> https://lore.kernel.org/linux-arm-kernel/1600332402-30123-1-git-send-email-anshuman.khandual@arm.com/
> 
> This mechanism focuses on the addressibility aspect and not [sub] section
> alignment aspect. Hence check_hotplug_memory_range() and check_pfn_span()
> have been left unchanged. Wondering if all these can still be unified in
> an expanded memhp_range_allowed() check, that can be called from multiple
> memory hot add and remove paths.
> 
> This series applies on v5.10-rc6 and has been slightly tested on arm64.
> But looking for some early feedback here.
> 
> Changes in RFC V2:
> 
> Incorporated all review feedbacks from David.
> 
> - Added additional range check in __segment_load() on s390 which was lost
> - Changed is_private init in pagemap_range()
> - Moved the framework into mm/memory_hotplug.c
> - Made arch_get_addressable_range() a __weak function
> - Renamed arch_get_addressable_range() as arch_get_mappable_range()
> - Callback arch_get_mappable_range() only handles range requiring linear mapping
> - Merged multiple memhp_range_allowed() checks in register_memory_resource()
> - Replaced WARN() with pr_warn() in memhp_range_allowed()
> - Replaced error return code ERANGE with E2BIG

There is one build failure with MEMORY_HOTPLUG=y and MEMORY_HOTREMOVE=n.
There are warnings on arm64 and s390 platforms when built with W=1 due
to lack of prototypes required with -Wmissing-prototypes. I have fixed
all these problems for the next iteration when there is broad agreement
on the overall approach.