linux-kernel - Re: [PATCH] arm64:free_initrd_mem should also free the memblock

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Message-ID: <20140915185027.GC30737@arm.com>
Date:	Mon, 15 Sep 2014 19:50:27 +0100
From:	Will Deacon <will.deacon@....com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	"Wang, Yalin" <Yalin.Wang@...ymobile.com>,
	"'linux-kernel@...r.kernel.org'" <linux-kernel@...r.kernel.org>,
	"'linux-arm-kernel@...ts.infradead.org'" 
	<linux-arm-kernel@...ts.infradead.org>,
	"'linux-mm@...ck.org'" <linux-mm@...ck.org>
Subject: Re: [PATCH] arm64:free_initrd_mem should also free the memblock

On Mon, Sep 15, 2014 at 07:40:23PM +0100, Russell King - ARM Linux wrote:
> On Mon, Sep 15, 2014 at 07:33:34PM +0100, Will Deacon wrote:
> > On Fri, Sep 12, 2014 at 11:17:18AM +0100, Wang, Yalin wrote:
> > > this patch fix the memblock statics for memblock
> > > in file /sys/kernel/debug/memblock/reserved
> > > if we don't call memblock_free the initrd will still
> > > be marked as reserved, even they are freed.
> > > 
> > > Signed-off-by: Yalin Wang <yalin.wang@...ymobile.com>
> > > ---
> > >  arch/arm64/mm/init.c | 4 +++-
> > >  1 file changed, 3 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> > > index 5472c24..34605c8 100644
> > > --- a/arch/arm64/mm/init.c
> > > +++ b/arch/arm64/mm/init.c
> > > @@ -334,8 +334,10 @@ static int keep_initrd;
> > >  
> > >  void free_initrd_mem(unsigned long start, unsigned long end)
> > >  {
> > > -	if (!keep_initrd)
> > > +	if (!keep_initrd) {
> > >  		free_reserved_area((void *)start, (void *)end, 0, "initrd");
> > > +		memblock_free(__pa(start), end - start);
> > > +	}
> > 
> > I don't think it makes any technical difference, but doing the memblock_free
> > before the free_reserved_area makes more sense to me.
> 
> A better question is... should we even be doing this.  The memblock
> information is used as a method to bring up the kernel and provide
> early allocation.  Once the memory is handed over from memblock to
> the normal kernel page allocators, we no longer care what happens to
> memblock.
> 
> There is no need to free the initrd memory back into memblock.  In
> fact, seeing the initrd location in /sys/kernel/debug/memblock/reserved
> can be useful debug information in itself.

That's a fair point. Yang: do you have a specific use-case in mind for this?

I wondered if it might interact with our pfn_valid implementation, which
uses memblock_is_memory, however memblock_free only deals with the reserved
regions, so I now I can't see why this change is required either.

Will
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