Re: [Xen-devel] [PATCH] mm: fix regression with deferred struct page init

[Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>]

On Thu, 2019-06-20 at 18:08 +0200, Juergen Gross wrote:
> Commit 0e56acae4b4dd4a9 ("mm: initialize MAX_ORDER_NR_PAGES at a time
> instead of doing larger sections") is causing a regression on some
> systems when the kernel is booted as Xen dom0.
> 
> The system will just hang in early boot.
> 
> Reason is an endless loop in get_page_from_freelist() in case the first
> zone looked at has no free memory. deferred_grow_zone() is always
> returning true due to the following code snipplet:
> 
>   /* If the zone is empty somebody else may have cleared out the zone */
>   if (!deferred_init_mem_pfn_range_in_zone(&i, zone, &spfn, &epfn,
>                                            first_deferred_pfn)) {
>           pgdat->first_deferred_pfn = ULONG_MAX;
>           pgdat_resize_unlock(pgdat, &flags);
>           return true;
>   }
> 
> This in turn results in the loop as get_page_from_freelist() is
> assuming forward progress can be made by doing some more struct page
> initialization.
> 
> Cc: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>
> Fixes: 0e56acae4b4dd4a9 ("mm: initialize MAX_ORDER_NR_PAGES at a time instead 
> of doing larger sections")
> Suggested-by: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>

Acked-by: Alexander Duyck <alexander.h.duyck@xxxxxxxxxxxxxxx>

> ---
>  mm/page_alloc.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index d66bc8abe0af..8e3bc949ebcc 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1826,7 +1826,8 @@ deferred_grow_zone(struct zone *zone, unsigned int 
> order)
>                                                first_deferred_pfn)) {
>               pgdat->first_deferred_pfn = ULONG_MAX;
>               pgdat_resize_unlock(pgdat, &flags);
> -             return true;
> +             /* Retry only once. */
> +             return first_deferred_pfn != ULONG_MAX;
>       }
>  
>       /*



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