Re: [PATCH] mm/compaction: fix the total_isolated in strict mode

[Andrew Morton]

On Sat,  2 Nov 2024 20:16:21 +0000 Qiang Liu <liuq131@xxxxxxxxxxxxxxx> wrote:

> If the last cycle reads bogus compound_order() and blockpfn > end_pfn occurs,
> it is possible that total_isolated will be less than nr_scanned. In this case,
> strict mode should return 0, but the “if (strict && blockpfn < end_pfn)”
> statement cannot recognize this situation
> 
> ...
>
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -699,7 +699,7 @@ static unsigned long isolate_freepages_block(struct compact_control *cc,
>  	 * pages requested were isolated. If there were any failures, 0 is
>  	 * returned and CMA will fail.
>  	 */
> -	if (strict && blockpfn < end_pfn)
> +	if (strict && (blockpfn < end_pfn || total_isolated != nr_scanned))
>  		total_isolated = 0;
>  
>  	cc->total_free_scanned += nr_scanned;

That's really old code.  What userspace-visible effects might this
have?  Is this from code inspection, or was some misbehaviour observed?

Thanks.