linux-kernel - Re: [PATCH V3 1/3] mm/memory_hotplug: Prevalidate the address range being added with platform

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Message-ID: <20210120115814.GA7107@localhost.localdomain>
Date:   Wed, 20 Jan 2021 12:58:14 +0100
From:   Oscar Salvador <osalvador@...e.de>
To:     David Hildenbrand <david@...hat.com>
Cc:     Anshuman Khandual <anshuman.khandual@....com>, linux-mm@...ck.org,
        akpm@...ux-foundation.org, hca@...ux.ibm.com,
        catalin.marinas@....com, Vasily Gorbik <gor@...ux.ibm.com>,
        Will Deacon <will@...nel.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V3 1/3] mm/memory_hotplug: Prevalidate the address range
 being added with platform

On Wed, Jan 20, 2021 at 11:41:53AM +0100, David Hildenbrand wrote:
> On 20.01.21 09:33, Anshuman Khandual wrote:
> > 
> > 
> > On 1/19/21 5:51 PM, David Hildenbrand wrote:
> >> On 18.01.21 14:12, Anshuman Khandual wrote:
> >>> This introduces memhp_range_allowed() which can be called in various memory
> >>> hotplug paths to prevalidate the address range which is being added, with
> >>> the platform. Then memhp_range_allowed() calls memhp_get_pluggable_range()
> >>> which provides applicable address range depending on whether linear mapping
> >>> is required or not. For ranges that require linear mapping, it calls a new
> >>> arch callback arch_get_mappable_range() which the platform can override. So
> >>> the new callback, in turn provides the platform an opportunity to configure
> >>> acceptable memory hotplug address ranges in case there are constraints.
> >>>
> >>> This mechanism will help prevent platform specific errors deep down during
> >>> hotplug calls. This drops now redundant check_hotplug_memory_addressable()
> >>> check in __add_pages() but instead adds a VM_BUG_ON() check which would
> >>
> >> In this patch, you keep the __add_pages() checks. But as discussed, we
> >> could perform it in mm/memremap.c:pagemap_range() insted and convert it
> >> to a VM_BUG_ON().
> > 
> > Just to be sure, will the following change achieve what you are
> > suggesting here. pagemap_range() after this change, will again
> > be the same like the V1 series.
> 
> Yeah, as we used to have in v1. Maybe other reviewers (@Oscar?) have a
> different opinion.

No, I think that placing the check in pagemap_range() out of the if-else
makes much more sense.
Actually, unless my memory  fails me that is what I suggested in v2.

I plan to have a look at the series later this week as I am fairly busy
atm.

Thanks


-- 
Oscar Salvador
SUSE L3