linux-kernel - Re: [PATCH v1 2/4] memblock: update initialization of reserved pages

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Date:   Tue, 20 Apr 2021 18:25:01 +0300
From:   Mike Rapoport <rppt@...nel.org>
To:     David Hildenbrand <david@...hat.com>
Cc:     linux-arm-kernel@...ts.infradead.org,
        Anshuman Khandual <anshuman.khandual@....com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Marc Zyngier <maz@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Will Deacon <will@...nel.org>, kvmarm@...ts.cs.columbia.edu,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v1 2/4] memblock: update initialization of reserved pages

On Tue, Apr 20, 2021 at 05:18:55PM +0200, David Hildenbrand wrote:
> On 20.04.21 17:03, Mike Rapoport wrote:
> > On Tue, Apr 20, 2021 at 03:56:28PM +0200, David Hildenbrand wrote:
> > > On 20.04.21 11:09, Mike Rapoport wrote:
> > > > From: Mike Rapoport <rppt@...ux.ibm.com>
> > > > 
> > > > The struct pages representing a reserved memory region are initialized
> > > > using reserve_bootmem_range() function. This function is called for each
> > > > reserved region just before the memory is freed from memblock to the buddy
> > > > page allocator.
> > > > 
> > > > The struct pages for MEMBLOCK_NOMAP regions are kept with the default
> > > > values set by the memory map initialization which makes it necessary to
> > > > have a special treatment for such pages in pfn_valid() and
> > > > pfn_valid_within().
> > > 
> > > Just a general question while thinking about it:
> > > 
> > > Would we right now initialize the memmap of these pages already via
> > > memmap_init_zone()->memmap_init_range()? (IOW, not marking the
> > > PageReserved?)
> > 
> > Yep. These pages are part of memblock.memory so they are initialized in
> > memmap_init_zone()->memmap_init_range() to the default values.
> > 
> 
> So instead of fully initializing them again, we mostly would only have to
> set PageReserved(). Not sure how big that memory usually is -- IOW, if we
> really care about optimizing the double-init.

IIUC, these are small areas reserved by the firmware, like e.g. ACPI
tables.

@Ard, am I right?

-- 
Sincerely yours,
Mike.