Re: [PATCH] mm: add cond_resched() in swapin_walk_pmd_entry()

[Andrew Morton]

On Mon, 5 Dec 2022 22:03:27 +0800 Kefeng Wang <wangkefeng.wang@xxxxxxxxxx> wrote:

> When handle MADV_WILLNEED in madvise(), the soflockup may be occurred
> in swapin_walk_pmd_entry() if swapin lots of memory on slow device,
> add a cond_resched() into it to avoid the possible softlockup.
> 
> ...
>
> --- a/mm/madvise.c
> +++ b/mm/madvise.c
> @@ -226,6 +226,7 @@ static int swapin_walk_pmd_entry(pmd_t *pmd, unsigned long start,
>  			put_page(page);
>  	}
>  	swap_read_unplug(splug);
> +	cond_resched();
>  
>  	return 0;
>  }

I wonder if this would be better in walk_pmd_range(), to address other
very large walk attempts.