linux-kernel - Re: [RFC 1/2] mm: Uncharge poisoned pages

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Date:   Mon, 24 Apr 2017 09:05:31 +0000
From:   Naoya Horiguchi <n-horiguchi@...jp.nec.com>
To:     Laurent Dufour <ldufour@...ux.vnet.ibm.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
Subject: Re: [RFC 1/2] mm: Uncharge poisoned pages

On Thu, Apr 20, 2017 at 11:26:01AM +0200, Laurent Dufour wrote:
> When page are poisoned, they should be uncharged from the root memory
> cgroup.

Could you include some information about what problem this patch tries
to solve?
# I know that you already explain it in patch 0/2, so you can simply
# copy from it.

>
> Signed-off-by: Laurent Dufour <ldufour@...ux.vnet.ibm.com>
> ---
>  mm/memory-failure.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> index 27f7210e7fab..00bd39d3d4cb 100644
> --- a/mm/memory-failure.c
> +++ b/mm/memory-failure.c
> @@ -530,6 +530,7 @@ static const char * const action_page_types[] = {
>  static int delete_from_lru_cache(struct page *p)
>  {
>  	if (!isolate_lru_page(p)) {
> +		memcg_kmem_uncharge(p, 0);

This function is supposed to be called with if (memcg_kmem_enabled()) check,
so could you do like below?

+		if (memcg_kmem_enabled())
+			memcg_kmem_uncharge(p, 0);

And I feel that we can call this function outside if (!isolate_lru_page(p))
block, because isolate_lru_page could fail and then the error page is left
incompletely isolated. Such error page has PageHWPoison set, so I guess that
the reported bug still triggers on such case.

Thanks,
Naoya Horiguchi