Re: [PATCH v5 1/1] mm: refactor initialization of struct page for holes in memory layout

[Mike Rapoport <rppt@kernel.org>]

Hi Vlastimil,

On Tue, Feb 16, 2021 at 05:39:12PM +0100, Vlastimil Babka wrote:
> 
> 
> So, Andrea could you please check if this fixes the original
> fast_isolate_around() issue for you? With the VM_BUG_ON not removed, DEBUG_VM
> enabled, no changes to struct page initialization...
> It relies on pageblock_pfn_to_page as the rest of the compaction code.

Pardon my ignorance of compaction internals, but does this mean that with
your patch we'll never call set_pfnblock_flags_mask() for a pfn in a hole?
 
> Thanks!
> 
> ----8<----
> From f5c8d7bc77d2ec0b4cfec44820ce6f602fdb3a86 Mon Sep 17 00:00:00 2001
> From: Vlastimil Babka <vbabka@suse.cz>
> Date: Tue, 16 Feb 2021 17:32:34 +0100
> Subject: [PATCH] mm, compaction: make fast_isolate_around() robust against
>  pfns from a wrong zone
> 
> TBD
> 
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
> ---
>  mm/compaction.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 190ccdaa6c19..b75645e4678d 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -1288,7 +1288,7 @@ static void
>  fast_isolate_around(struct compact_control *cc, unsigned long pfn, unsigned long nr_isolated)
>  {
>  	unsigned long start_pfn, end_pfn;
> -	struct page *page = pfn_to_page(pfn);
> +	struct page *page;
>  
>  	/* Do not search around if there are enough pages already */
>  	if (cc->nr_freepages >= cc->nr_migratepages)
> @@ -1300,7 +1300,11 @@ fast_isolate_around(struct compact_control *cc, unsigned long pfn, unsigned long
>  
>  	/* Pageblock boundaries */
>  	start_pfn = pageblock_start_pfn(pfn);
> -	end_pfn = min(pageblock_end_pfn(pfn), zone_end_pfn(cc->zone)) - 1;
> +	end_pfn = min(pageblock_end_pfn(pfn), zone_end_pfn(cc->zone));
> +
> +	page = pageblock_pfn_to_page(start_pfn, end_pfn, cc->zone);
> +	if (!page)
> +		return;
>  
>  	/* Scan before */
>  	if (start_pfn != pfn) {
> @@ -1486,7 +1490,7 @@ fast_isolate_freepages(struct compact_control *cc)
>  	}
>  
>  	cc->total_free_scanned += nr_scanned;
> -	if (!page)
> +	if (!page || page_zone(page) != cc->zone)
>  		return cc->free_pfn;
>  
>  	low_pfn = page_to_pfn(page);
> -- 
> 2.30.0
> 

-- 
Sincerely yours,
Mike.