Re: [PATCH v2 1/2] mm: Uncharge poisoned pages

From	Laurent Dufour <ldufour@linux.vnet.ibm.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH v2 1/2] mm: Uncharge poisoned pages
Date	2017-04-28 11:40 +0200
Message-ID	<tBaxA-5vx-7@gated-at.bofh.it> (permalink)
References	(2 earlier) <tAkpj-43b-5@gated-at.bofh.it> <tAlEJ-54X-5@gated-at.bofh.it> <tAm7L-5dT-3@gated-at.bofh.it> <tAn3P-5Rf-3@gated-at.bofh.it> <tAr7r-bV-19@gated-at.bofh.it>
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On 26/04/2017 10:59, Balbir Singh wrote:
> On Wed, 2017-04-26 at 04:46 +0000, Naoya Horiguchi wrote:
>> On Wed, Apr 26, 2017 at 01:45:00PM +1000, Balbir Singh wrote:
>>>>>>  static int delete_from_lru_cache(struct page *p)
>>>>>>  {
>>>>>> +	if (memcg_kmem_enabled())
>>>>>> +		memcg_kmem_uncharge(p, 0);
>>>>>> +
>>>>>
>>>>> The changelog is not quite clear, so we are uncharging a page using
>>>>> memcg_kmem_uncharge for a page in swap cache/page cache?
>>>>
>>>> Hi Balbir,
>>>>
>>>> Yes, in the normal page lifecycle, uncharge is done in page free time.
>>>> But in memory error handling case, in-use pages (i.e. swap cache and page
>>>> cache) are removed from normal path and they don't pass page freeing code.
>>>> So I think that this change is to keep the consistent charging for such a case.
>>>
>>> I agree we should uncharge, but looking at the API name, it seems to
>>> be for kmem pages, why are we not using mem_cgroup_uncharge()? Am I missing
>>> something?
>>
>> Thank you for pointing out.
>> Actually I had the same question and this surely looks strange.
>> But simply calling mem_cgroup_uncharge() here doesn't work because it
>> assumes that page_refcount(p) == 0, which is not true in hwpoison context.
>> We need some other clearer way or at least some justifying comment about
>> why this is ok.
>>
> 
> We should call mem_cgroup_uncharge() after isolate_lru_page()/put_page().

Thanks for the review Naoya and Balbir,

I changed the patch to call mem_cgroup_uncharge() once
isolate_lru_page() succeeded, but before calling put_page().
It seems to work fine.

> We could check if page_count() is 0 or force if required (!MF_RECOVERED &&
> !MF_DELAYED). We could even skip the VM_BUG_ON if the page is poisoned.

This doesn't seem to be needed. Am I still missing something here ?

Cheers,
Laurent.

Thread

[PATCH v2 0/2] BUG raised when onlining HWPoisoned page Laurent Dufour <ldufour@linux.vnet.ibm.com> - 2017-04-25 16:30 +0200
  [PATCH v2 2/2] mm: skip HWPoisoned pages when onlining pages Laurent Dufour <ldufour@linux.vnet.ibm.com> - 2017-04-25 16:30 +0200
    Re: [PATCH v2 2/2] mm: skip HWPoisoned pages when onlining pages Balbir Singh <bsingharora@gmail.com> - 2017-04-26 04:20 +0200
      Re: [PATCH v2 2/2] mm: skip HWPoisoned pages when onlining pages Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> - 2017-04-26 05:30 +0200
        Re: [PATCH v2 2/2] mm: skip HWPoisoned pages when onlining pages Balbir Singh <bsingharora@gmail.com> - 2017-04-28 05:00 +0200
        Re: [PATCH v2 2/2] mm: skip HWPoisoned pages when onlining pages Michal Hocko <mhocko@kernel.org> - 2017-04-28 08:40 +0200
          Re: [PATCH v2 2/2] mm: skip HWPoisoned pages when onlining pages Michal Hocko <mhocko@kernel.org> - 2017-04-28 09:00 +0200
            Re: [PATCH v2 2/2] mm: skip HWPoisoned pages when onlining pages Michal Hocko <mhocko@kernel.org> - 2017-05-10 09:50 +0200
          Re: [PATCH v2 2/2] mm: skip HWPoisoned pages when onlining pages Michal Hocko <mhocko@kernel.org> - 2017-04-28 09:00 +0200
  [PATCH v2 1/2] mm: Uncharge poisoned pages Laurent Dufour <ldufour@linux.vnet.ibm.com> - 2017-04-25 16:30 +0200
    Re: [PATCH v2 1/2] mm: Uncharge poisoned pages Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> - 2017-04-26 02:00 +0200
    Re: [PATCH v2 1/2] mm: Uncharge poisoned pages Balbir Singh <bsingharora@gmail.com> - 2017-04-26 04:00 +0200
      Re: [PATCH v2 1/2] mm: Uncharge poisoned pages Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> - 2017-04-26 05:20 +0200
        Re: [PATCH v2 1/2] mm: Uncharge poisoned pages Balbir Singh <bsingharora@gmail.com> - 2017-04-26 05:50 +0200
          Re: [PATCH v2 1/2] mm: Uncharge poisoned pages Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> - 2017-04-26 06:50 +0200
            Re: [PATCH v2 1/2] mm: Uncharge poisoned pages Balbir Singh <bsingharora@gmail.com> - 2017-04-26 11:10 +0200
              Re: [PATCH v2 1/2] mm: Uncharge poisoned pages Laurent Dufour <ldufour@linux.vnet.ibm.com> - 2017-04-28 11:40 +0200
    Re: [PATCH v2 1/2] mm: Uncharge poisoned pages Michal Hocko <mhocko@kernel.org> - 2017-04-27 16:40 +0200
      Re: [PATCH v2 1/2] mm: Uncharge poisoned pages Andi Kleen <andi@firstfloor.org> - 2017-04-27 23:00 +0200
        Re: [PATCH v2 1/2] mm: Uncharge poisoned pages Michal Hocko <mhocko@kernel.org> - 2017-04-28 08:10 +0200
          Re: [PATCH v2 1/2] mm: Uncharge poisoned pages Michal Hocko <mhocko@kernel.org> - 2017-04-28 09:40 +0200
            Re: [PATCH v2 1/2] mm: Uncharge poisoned pages Laurent Dufour <ldufour@linux.vnet.ibm.com> - 2017-04-28 11:20 +0200
              Re: [PATCH v2 1/2] mm: Uncharge poisoned pages Michal Hocko <mhocko@kernel.org> - 2017-04-28 15:50 +0200
                Re: [PATCH v2 1/2] mm: Uncharge poisoned pages Laurent Dufour <ldufour@linux.vnet.ibm.com> - 2017-05-02 17:00 +0200
                Re: [PATCH v2 1/2] mm: Uncharge poisoned pages Michal Hocko <mhocko@kernel.org> - 2017-05-02 21:00 +0200
                Re: [PATCH v2 1/2] mm: Uncharge poisoned pages Laurent Dufour <ldufour@linux.vnet.ibm.com> - 2017-05-03 13:40 +0200
                Re: [PATCH v2 1/2] mm: Uncharge poisoned pages Balbir Singh <bsingharora@gmail.com> - 2017-05-04 03:30 +0200
                Re: [PATCH v2 1/2] mm: Uncharge poisoned pages Laurent Dufour <ldufour@linux.vnet.ibm.com> - 2017-05-08 12:50 +0200
                Re: [PATCH v2 1/2] mm: Uncharge poisoned pages Balbir Singh <bsingharora@gmail.com> - 2017-05-09 03:50 +0200
                Re: [PATCH v2 1/2] mm: Uncharge poisoned pages Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> - 2017-05-08 05:10 +0200
                Re: [PATCH v2 1/2] mm: Uncharge poisoned pages Michal Hocko <mhocko@kernel.org> - 2017-05-09 11:20 +0200
                Re: [PATCH v2 1/2] mm: Uncharge poisoned pages Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> - 2017-05-10 01:10 +0200

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