linux-kernel - Re: [PATCH] Revert "mm/memblock.c: hardcode the end

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Date:   Fri, 16 Mar 2018 11:27:25 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Jia He <hejianet@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        Catalin Marinas <catalin.marinas@....com>,
        Pavel Tatashin <pasha.tatashin@...cle.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        AKASHI Takahiro <takahiro.akashi@...aro.org>,
        Gioh Kim <gi-oh.kim@...fitbricks.com>,
        Daniel Vacek <neelx@...hat.com>, linux-kernel@...r.kernel.org,
        Jia He <jia.he@...-semitech.com>
Subject: Re: [PATCH] Revert "mm/memblock.c: hardcode the end_pfn being -1"

On Fri 16-03-18 17:26:57, Jia He wrote:
> 
> 
> On 3/16/2018 5:06 PM, Michal Hocko Wrote:
> > On Thu 15-03-18 19:56:06, Jia He wrote:
> > > This reverts commit 379b03b7fa05f7db521b7732a52692448a3c34fe.
> > > 
> > > Commit 864b75f9d6b0 ("mm/page_alloc: fix memmap_init_zone pageblock
> > > alignment") introduced boot hang issues in arm/arm64 machines, so
> > > Ard Biesheuvel reverted in commit 3e04040df6d4. But there is a
> > > preparation patch for commit 864b75f9d6b0. So just revert it for
> > > the sake of caution.
> > Why? Is there anything wrong with this one?
> I don't think there might be anything wrong. Justin for the sake of caution.
> Please ignore this patch if you prefer to keep 379b03b7fa.

We do not revert just if the patch is correct. I do not have strong
preference for the patch but I also do not see anything wrong with it.

> But seems parameter *max_pfn* is useless and can be removed in this case?

A patch for that is already sitting in mmotm tree

> Cheers,
> Jia
> > > Signed-off-by: Jia He <jia.he@...-semitech.com>
> > > ---
> > >   mm/memblock.c | 10 +++++-----
> > >   1 file changed, 5 insertions(+), 5 deletions(-)
> > > 
> > > diff --git a/mm/memblock.c b/mm/memblock.c
> > > index b6ba6b7..5a9ca2a 100644
> > > --- a/mm/memblock.c
> > > +++ b/mm/memblock.c
> > > @@ -1107,7 +1107,7 @@ unsigned long __init_memblock memblock_next_valid_pfn(unsigned long pfn,
> > >   	struct memblock_type *type = &memblock.memory;
> > >   	unsigned int right = type->cnt;
> > >   	unsigned int mid, left = 0;
> > > -	phys_addr_t addr = PFN_PHYS(++pfn);
> > > +	phys_addr_t addr = PFN_PHYS(pfn + 1);
> > >   	do {
> > >   		mid = (right + left) / 2;
> > > @@ -1118,15 +1118,15 @@ unsigned long __init_memblock memblock_next_valid_pfn(unsigned long pfn,
> > >   				  type->regions[mid].size))
> > >   			left = mid + 1;
> > >   		else {
> > > -			/* addr is within the region, so pfn is valid */
> > > -			return pfn;
> > > +			/* addr is within the region, so pfn + 1 is valid */
> > > +			return min(pfn + 1, max_pfn);
> > >   		}
> > >   	} while (left < right);
> > >   	if (right == type->cnt)
> > > -		return -1UL;
> > > +		return max_pfn;
> > >   	else
> > > -		return PHYS_PFN(type->regions[right].base);
> > > +		return min(PHYS_PFN(type->regions[right].base), max_pfn);
> > >   }
> > >   /**
> > > -- 
> > > 2.7.4
> > > 

-- 
Michal Hocko
SUSE Labs