linux-kernel - Re: [PATCH] mm: fix regression with deferred struct page init

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Message-ID: <79797c17-58d6-b09c-3aad-73e375a7f208@suse.com>
Date:   Tue, 25 Jun 2019 10:25:33 +0200
From:   Juergen Gross <jgross@...e.com>
To:     xen-devel@...ts.xenproject.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Cc:     Alexander Duyck <alexander.h.duyck@...ux.intel.com>
Subject: Re: [PATCH] mm: fix regression with deferred struct page init

Gentle ping.

I'd really like to have that in 5.2 in order to avoid the regression
introduced with 5.2-rc1.


Juergen

On 20.06.19 18:08, 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@...ux.intel.com>
> Fixes: 0e56acae4b4dd4a9 ("mm: initialize MAX_ORDER_NR_PAGES at a time instead of doing larger sections")
> Suggested-by: Alexander Duyck <alexander.h.duyck@...ux.intel.com>
> Signed-off-by: Juergen Gross <jgross@...e.com>
> ---
>   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;
>   	}
>   
>   	/*
>