linux-kernel - Re: vmscan: Reclaim unevictable pages

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Date:   Thu, 14 Mar 2019 09:41:20 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Pankaj Suryawanshi <pankaj.suryawanshi@...fochips.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "minchan@...nel.org" <minchan@...nel.org>
Subject: Re: vmscan: Reclaim unevictable pages

On Thu 14-03-19 08:23:10, Pankaj Suryawanshi wrote:
> 
> Below is the Error Msg :
> 
> [   24.718792] page dumped because: VM_BUG_ON_PAGE(PageLRU(page) || PageUnevictable(page))
> [   24.726949] page->mem_cgroup:bd008c00
> [   24.730693] ------------[ cut here ]------------
> [   24.735304] kernel BUG at mm/vmscan.c:1350!
> [   24.739478] Internal error: Oops - BUG: 0 [#1] PREEMPT SMP ARM

Just curious. Which kernel version is that? Are there any addional
patches applied on top of vanilla?
 
> Solved the issue by below patch.
> 
> 
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index be56e2e..2e51edc 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -990,15 +990,17 @@ static unsigned long shrink_page_list(struct list_head *page_list,
>                 page = lru_to_page(page_list);
>                 list_del(&page->lru);
> 
>                if (!trylock_page(page)) {
>                         goto keep;
>                }
> 
>                 VM_BUG_ON_PAGE(PageActive(page), page);
> 
>                 sc->nr_scanned++;
> 
>                 if (unlikely(!page_evictable(page)))
> -                       goto activate_locked;
> +                      goto cull_mlocked;
> 
>                 if (!sc->may_unmap && page_mapped(page))
>                         goto keep_locked;
> @@ -1331,6 +1333,12 @@ static unsigned long shrink_page_list(struct list_head *page_list,
>                 } else
>                         list_add(&page->lru, &free_pages);
>                 continue;
> +cull_mlocked:
> +                if (PageSwapCache(page))
> +                        try_to_free_swap(page);
> +                unlock_page(page);
> +                list_add(&page->lru, &ret_pages);
> +                continue;
> 
>  activate_locked:
>                 /* Not a candidate for swapping, so reclaim swap space. */
> 
> 
> 
> 
> From: Pankaj Suryawanshi
> Sent: 14 March 2019 13:23:53
> To: linux-kernel@...r.kernel.org
> Cc: minchan@...nel.org
> Subject: vmscan: Reclaim unevictable pages
> 
> 
> 
> Hello ,
> 
> shrink_page_list() returns , number of pages reclaimed, when pages is unevictable it returns VM_BUG_ON_PAGE(PageLRU(page) || PageUnevicatble(page),page);
> 
> We can add the unevictable pages in reclaim list in shrink_page_list(), return total number of reclaim pages including unevictable pages, let the caller handle unevictable pages.
> 
> Regards,
> Pankaj
> 
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-- 
Michal Hocko
SUSE Labs