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

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Date:   Mon, 24 Apr 2017 15:15:59 +0200
From:   Laurent Dufour <ldufour@...ux.vnet.ibm.com>
To:     Naoya Horiguchi <n-horiguchi@...jp.nec.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 24/04/2017 11:05, Naoya Horiguchi wrote:
> 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.

Thanks for the review, I will add the BUG's output in the next version.

> 
>>
>> 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.

I move the call to memcg_kmem_uncharge() outside if
(!isolate_lru_page(p)) and it seems to work as well.

I'll wait a bit for any other review to come and I'll send a new version.

Thanks,
Laurent.