Re: [PATCH] thp: do not adjust zone water marks if khugepaged is not started

["Kirill A. Shutemov" <kirill@shutemov.name>]

On Fri, Mar 27, 2015 at 03:00:26PM -0700, Andrew Morton wrote:
> On Fri, 27 Mar 2015 14:47:08 -0700 Andrew Morton <akpm@linux-foundation.org> wrote:
> 
> > Fair enough, but take a look at start_khugepaged():
> > 
> > : static int start_khugepaged(void)
> > : {
> > : 	int err = 0;
> > : 	if (khugepaged_enabled()) {
> > : 		if (!khugepaged_thread)
> > : 			khugepaged_thread = kthread_run(khugepaged, NULL,
> > : 							"khugepaged");
> > : 		if (unlikely(IS_ERR(khugepaged_thread))) {
> > : 			pr_err("khugepaged: kthread_run(khugepaged) failed\n");
> > : 			err = PTR_ERR(khugepaged_thread);
> > : 			khugepaged_thread = NULL;
> > 
> > -->> stop here 
> > 
> > : 		}
> > : 
> > : 		if (!list_empty(&khugepaged_scan.mm_head))
> > : 			wake_up_interruptible(&khugepaged_wait);
> > : 
> > : 		set_recommended_min_free_kbytes();
> > : 	} else if (khugepaged_thread) {
> > : 		kthread_stop(khugepaged_thread);
> > : 		khugepaged_thread = NULL;
> > : 	}
> > : 
> > : 	return err;
> > : }
> 
> Looking more closely...  This code seems a bit screwy.
> 
> - why is set_recommended_min_free_kbytes() a late_initcall?  We've
>   already done that within
>   subsys_initcall->hugepage_init->set_recommended_min_free_kbytes()
> 
> - there isn't much point in running start_khugepaged() if we've just
>   set transparent_hugepage_flags to zero.
> 
> - start_khugepaged() is misnamed.
> 
> So something like this?

Yeah, looks good to me.

> --- a/mm/huge_memory.c~a
> +++ a/mm/huge_memory.c
> @@ -110,10 +110,6 @@ static int set_recommended_min_free_kbyt
>  	int nr_zones = 0;
>  	unsigned long recommended_min;
>  
> -	/* khugepaged thread has stopped to failed to start */
> -	if (!khugepaged_thread)
> -		return 0;
> -
>  	for_each_populated_zone(zone)
>  		nr_zones++;
>  
> @@ -145,9 +141,8 @@ static int set_recommended_min_free_kbyt
>  	setup_per_zone_wmarks();
>  	return 0;
>  }
> -late_initcall(set_recommended_min_free_kbytes);
>  
> -static int start_khugepaged(void)
> +static int start_stop_khugepaged(void)
>  {
>  	int err = 0;
>  	if (khugepaged_enabled()) {
> @@ -158,6 +153,7 @@ static int start_khugepaged(void)
>  			pr_err("khugepaged: kthread_run(khugepaged) failed\n");
>  			err = PTR_ERR(khugepaged_thread);
>  			khugepaged_thread = NULL;
> +			goto fail;
>  		}
>  
>  		if (!list_empty(&khugepaged_scan.mm_head))
> @@ -168,7 +164,7 @@ static int start_khugepaged(void)
>  		kthread_stop(khugepaged_thread);
>  		khugepaged_thread = NULL;
>  	}
> -
> +fail:
>  	return err;
>  }
>  
> @@ -302,7 +298,7 @@ static ssize_t enabled_store(struct kobj
>  		int err;
>  
>  		mutex_lock(&khugepaged_mutex);
> -		err = start_khugepaged();
> +		err = start_stop_khugepaged();
>  		mutex_unlock(&khugepaged_mutex);
>  
>  		if (err)
> @@ -651,12 +647,13 @@ static int __init hugepage_init(void)
>  	 * where the extra memory used could hurt more than TLB overhead
>  	 * is likely to save.  The admin can still enable it through /sys.
>  	 */
> -	if (totalram_pages < (512 << (20 - PAGE_SHIFT)))
> +	if (totalram_pages < (512 << (20 - PAGE_SHIFT))) {
>  		transparent_hugepage_flags = 0;
> -
> -	err = start_khugepaged();
> -	if (err)
> -		goto err_khugepaged;
> +	} else {
> +		err = start_stop_khugepaged();
> +		if (err)
> +			goto err_khugepaged;
> +	}
>  
>  	return 0;
>  err_khugepaged:
> _
> 
> --
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-- 
 Kirill A. Shutemov

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