Re: [PATCH v3 1/5] mm: page_alloc: remain memblock_next_valid_pfn() when CONFIG_HAVE_ARCH_PFN_VALID is enable

[Jia He]

On 3/28/2018 5:18 PM, Wei Yang Wrote:
> Oops, I should reply this thread. Forget about the reply on another thread.
>
> On Sun, Mar 25, 2018 at 08:02:15PM -0700, Jia He wrote:
> > Commit b92df1de5d28 ("mm: page_alloc: skip over regions of invalid pfns
> > where possible") optimized the loop in memmap_init_zone(). But it causes
> > possible panic bug. So Daniel Vacek reverted it later.
> Why this has a bug? Do you have some link about it?
>
> If the audience could know the potential risk, it would be helpful to review
> the code and decide whether to take it back.
Hi Wei
Paul firstly submit a commit b92df1de5 to improve the loop in 
memmap_init_zone.
And Daniel tried to fix a bug_on panic issue on X86 in commit 
864b75f9d6b because
there is evidence that this bug_on was caused by b92df1de5 [1].

But things didn't get better, 864b75f9d6b caused booting hang issue on 
arm{64} [2]
So maintainer decided to reverted both b92df1de5 and 864b75f9d6b

[1] https://patchwork.kernel.org/patch/10251145/
[2] https://lkml.org/lkml/2018/3/14/469
> > But memblock_next_valid_pfn is valid when CONFIG_HAVE_ARCH_PFN_VALID is
> > enable. And as verified by Eugeniu Rosca, arm can benifit from this
> > commit. So remain the memblock_next_valid_pfn.
> >
> > Signed-off-by: Jia He <jia.he@xxxxxxxxxxxxxxxx>
> > ---
> > include/linux/memblock.h |  4 ++++
> > mm/memblock.c            | 29 +++++++++++++++++++++++++++++
> > mm/page_alloc.c          | 11 ++++++++++-
> > 3 files changed, 43 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/linux/memblock.h b/include/linux/memblock.h
> > index 0257aee..efbbe4b 100644
> > --- a/include/linux/memblock.h
> > +++ b/include/linux/memblock.h
> > @@ -203,6 +203,10 @@ void __next_mem_pfn_range(int *idx, int nid, unsigned long *out_start_pfn,
> > 	     i >= 0; __next_mem_pfn_range(&i, nid, p_start, p_end, p_nid))
> > #endif /* CONFIG_HAVE_MEMBLOCK_NODE_MAP */
> >
> > +#ifdef CONFIG_HAVE_ARCH_PFN_VALID
> > +unsigned long memblock_next_valid_pfn(unsigned long pfn);
> > +#endif
> > +
> > /**
> >   * for_each_free_mem_range - iterate through free memblock areas
> >   * @i: u64 used as loop variable
> > diff --git a/mm/memblock.c b/mm/memblock.c
> > index ba7c878..bea5a9c 100644
> > --- a/mm/memblock.c
> > +++ b/mm/memblock.c
> > @@ -1102,6 +1102,35 @@ void __init_memblock __next_mem_pfn_range(int *idx, int nid,
> > 		*out_nid = r->nid;
> > }
> >
> > +#ifdef CONFIG_HAVE_ARCH_PFN_VALID
> > +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);
> > +
> > +	do {
> > +		mid = (right + left) / 2;
> > +
> > +		if (addr < type->regions[mid].base)
> > +			right = mid;
> > +		else if (addr >= (type->regions[mid].base +
> > +				  type->regions[mid].size))
> > +			left = mid + 1;
> > +		else {
> > +			/* addr is within the region, so pfn is valid */
> > +			return pfn;
> > +		}
> > +	} while (left < right);
> > +
> > +	if (right == type->cnt)
> > +		return -1UL;
> > +	else
> > +		return PHYS_PFN(type->regions[right].base);
> > +}
> > +#endif /*CONFIG_HAVE_ARCH_PFN_VALID*/
> > +
> > /**
> >   * memblock_set_node - set node ID on memblock regions
> >   * @base: base of area to set node ID for
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index c19f5ac..2a967f7 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -5483,8 +5483,17 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
> > 		if (context != MEMMAP_EARLY)
> > 			goto not_early;
> >
> > -		if (!early_pfn_valid(pfn))
> > +		if (!early_pfn_valid(pfn)) {
> > +#if (defined CONFIG_HAVE_MEMBLOCK) && (defined CONFIG_HAVE_ARCH_PFN_VALID)
> In commit b92df1de5d28, it use CONFIG_HAVE_MEMBLOCK_NODE_MAP.
>
> Not get the point of your change.
Please get more information about the reason why using 
CONFIG_HAVE_MEMBLOCK in
d49d47e mm: page_alloc: skip over regions of invalid pfns on UMA

And this commit is dependent on b92df1de, so it is also reverted.

Cheers,
Jia
> > +			/*
> > +			 * Skip to the pfn preceding the next valid one (or
> > +			 * end_pfn), such that we hit a valid pfn (or end_pfn)
> > +			 * on our next iteration of the loop.
> > +			 */
> > +			pfn = memblock_next_valid_pfn(pfn) - 1;
> > +#endif
> > 			continue;
> > +		}
> > 		if (!early_pfn_in_nid(pfn, nid))
> > 			continue;
> > 		if (!update_defer_init(pgdat, pfn, end_pfn, &nr_initialised))
> > --
> > 2.7.4

--
Cheers,
Jia