Re: [PATCH] mm/compaction: Fix the incorrect hole in fast_isolate_freepages()

[Baoquan He <bhe@redhat.com>]

On 05/22/20 at 03:01pm, Baoquan He wrote:
> > > As I said, the unavailable range includes firmware reserved ranges, and
> > > holes inside one boot memory section, if that boot memory section haves
> > > useable memory range, and firmware reserved ranges, and holes. Adding
> > > them all into memblock seems a little unreasonable, since they are never
> > > used by system in memblock, buddy or high level memory allocator. But I
> > > can see that adding them into memblock may have the same effect as the
> > > old code which is beofre your your patchset applied. Let's see if Mel or
> > > other people have some saying. I pesonally would not suggest doing it
> > > like this though.
> > 
> > Adding reserved regions to memblock.memory will not have the same effect
> > as the old code. We anyway have to initialize struct page for these
> > areas, but unlike the old code we don't need to run them by the
> > early_pfn_in_nid() checks and we still get rid the
> > CONFIG_NODES_SPAN_OTHER_NODES option.
> 
> Hmm, I mean adding them to memblock will let us have the same result,
> they are added into the node, zone where they should be, and marked as
> reserved, just as the old code did.
> 
> Rethink about this, seems adding them into memblock is doable. But
> we may not need to add them from e820 reserved range, since that will
> skip hole range which share the same section with usable range, and may
> need to change code in different ARCHes. How about this:
> 
> We add them into memblock in init_unavailable_range(), memmap_init() will
> add them into the right node and zone, reserve_bootmem_region() will
> initialize them and mark them as Reserved.
> 
> 
> From d019d0f9e7c958542dfcb142f93d07fcce6c7c22 Mon Sep 17 00:00:00 2001
> From: Baoquan He <bhe@redhat.com>
> Date: Fri, 22 May 2020 14:36:13 +0800
> Subject: [PATCH] mm/page_alloc.c: Add unavailable ranges into memblock
> 
> These unavailable ranges shares the same section with the usable range
> in boot memory, e.g the firmware reserved ranges, and holes.
> 
> Previously, they are added into node 0, zone 0 in function
> init_unavailable_range(), and marked as Reserved. Later, in function
> memmap_init(), they will be added to appropriate node and zone, where
> they are covered.
> 
> However, after the patchset ("mm: rework free_area_init*() funcitons")
> is applied, we change to iterate over memblock regions. These unavailable
> ranges are skipped, and the node and zone adjustment won't be done any
> more as the old code did. This cause a crash in compaction which is triggered
> by VM_BUG_ON_PAGE(!zone_spans_pfn(page_zone(page), pfn)).
> 
> So let's add these unavailable ranges into memblock and reserve them
> in init_unavailable_range() instead. With this change, they will be added
> into appropriate node and zone in memmap_init(), and initialized in
> reserve_bootmem_region() just like any other memblock reserved regions.

Seems this is not right. They can't get nid in init_unavailable_range().
Adding e820 ranges may let them get nid. But the hole range won't be
added to memblock, and still has the issue.

Nack this one for now, still considering.

> 
> Signed-off-by: Baoquan He <bhe@redhat.com>
> ---
>  mm/page_alloc.c | 17 +++++++++++------
>  1 file changed, 11 insertions(+), 6 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 603187800628..3973b5fdfe3f 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -6925,7 +6925,7 @@ static u64 __init init_unavailable_range(unsigned long spfn, unsigned long epfn)
>  static void __init init_unavailable_mem(void)
>  {
>  	phys_addr_t start, end;
> -	u64 i, pgcnt;
> +	u64 i, pgcnt, size;
>  	phys_addr_t next = 0;
>  
>  	/*
> @@ -6934,9 +6934,11 @@ static void __init init_unavailable_mem(void)
>  	pgcnt = 0;
>  	for_each_mem_range(i, &memblock.memory, NULL,
>  			NUMA_NO_NODE, MEMBLOCK_NONE, &start, &end, NULL) {
> -		if (next < start)
> -			pgcnt += init_unavailable_range(PFN_DOWN(next),
> -							PFN_UP(start));
> +		if (next < start) {
> +			size = PFN_UP(start) - PFN_DOWN(next);
> +			memblock_add(PFN_DOWN(next), size);
> +			memblock_reserve(PFN_DOWN(next), size);
> +		}
>  		next = end;
>  	}
>  
> @@ -6947,8 +6949,11 @@ static void __init init_unavailable_mem(void)
>  	 * considered initialized. Make sure that memmap has a well defined
>  	 * state.
>  	 */
> -	pgcnt += init_unavailable_range(PFN_DOWN(next),
> -					round_up(max_pfn, PAGES_PER_SECTION));
> +	size = round_up(max_pfn, PAGES_PER_SECTION) - PFN_DOWN(next);
> +	if (size) {
> +		memblock_add(PFN_DOWN(next), size);
> +		memblock_reserve(PFN_DOWN(next), size);
> +	}
>  
>  	/*
>  	 * Struct pages that do not have backing memory. This could be because
> -- 
> 2.17.2
>