linux-kernel - Re: [PATCHv2 2/2] mm: downgrade VM_BUG in isolate_lru

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Message-ID: <20160203145844.GJ6757@dhcp22.suse.cz>
Date:	Wed, 3 Feb 2016 15:58:44 +0100
From:	Michal Hocko <mhocko@...nel.org>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	David Rientjes <rientjes@...gle.com>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv2 2/2] mm: downgrade VM_BUG in isolate_lru_page() to
 warning

On Tue 02-02-16 19:21:01, Kirill A. Shutemov wrote:
> Calling isolate_lru_page() is wrong and shouldn't happen, but it not
> nessesary fatal: the page just will not be isolated if it's not on LRU.
> 
> Let's downgrade the VM_BUG_ON_PAGE() to WARN_RATELIMIT().

This will trigger for !CONFIG_DEBUG_VM as well which I am not sure is
necessary. I guess isolate_lru_page is not such a hot path so this would
be acceptable.

> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>

Anyway
Acked-by: Michal Hocko <mhocko@...e.com>

> ---
>  mm/vmscan.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index eb3dd37ccd7c..71b1c29948db 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1443,7 +1443,7 @@ int isolate_lru_page(struct page *page)
>  	int ret = -EBUSY;
>  
>  	VM_BUG_ON_PAGE(!page_count(page), page);
> -	VM_BUG_ON_PAGE(PageTail(page), page);
> +	WARN_RATELIMIT(PageTail(page), "trying to isolate tail page");
>  
>  	if (PageLRU(page)) {
>  		struct zone *zone = page_zone(page);
> -- 
> 2.7.0
> 

-- 
Michal Hocko
SUSE Labs