On 18.03.2019 12:43, Pankaj Suryawanshi wrote:
> Hi Kirill Tkhai,
>
Please, do not top posting: https://kernelnewbies.org/mailinglistguidelines
> Please see mm/vmscan.c in which it first added to list and than throw the
> error :
> --------------------------------------------------------------------------------------------------
> keep:
> list_add(&page->lru, &ret_pages);
> VM_BUG_ON_PAGE(PageLRU(page) || PageUnevictable(page), page);
> ---------------------------------------------------------------------------------------------------
>
> Before throwing error, pages are added to list, this is under iteration of
> shrink_page_list().
I say about about the list, which is passed to shrink_page_list() as first
argument.
shrink_inactive_list()
{
isolate_lru_pages(&page_list); // <-- you can't obtain unevictable
pages here.
shrink_page_list(&page_list);
}
> From: Kirill Tkhai <ktk...@virtuozzo.com>
> Sent: 18 March 2019 15:03:15
> To: Pankaj Suryawanshi; Vlastimil Babka; Michal Hocko;
> aneesh.ku...@linux.ibm.com
> Cc: linux-kernel@vger.kernel.org; minc...@kernel.org; linux...@kvack.org;
> khand...@linux.vnet.ibm.com; hillf...@alibaba-inc.com
> Subject: Re: [External] Re: vmscan: Reclaim unevictable pages
>
>
> Hi, Pankaj,
>
> On 18.03.2019 12:09, Pankaj Suryawanshi wrote:
>>
>> Hello
>>
>> shrink_page_list() returns , number of pages reclaimed, when pages is
>> unevictable it returns VM_BUG_ON_PAGE(PageLRU(page) ||
>> PageUnevicatble(page),page);
>
> the general idea is shrink_page_list() can't iterate PageUnevictable() pages.
> PageUnevictable() pages are never being added to lists, which
> shrink_page_list()
> uses for iteration. Also, a page can't be marked as PageUnevictable(), when
> it's attached to a shrinkable list.
>
> So, the problem should be somewhere outside shrink_page_list().
>
> I won't suggest you something about CMA, since I haven't dived in that code.
>
>> 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.
>>
>> I think the problem is shrink_page_list is awkard. If page is unevictable it
>> goto activate_locked->keep_locked->keep lables, keep lable list_add the
>> unevictable pages and throw the VM_BUG instead of passing it to caller while
>> it relies on caller for non-reclaimed-non-unevictable page's putback.
>> I think we can make it consistent so that shrink_page_list could return
>> non-reclaimed pages via page_list and caller can handle it. As an advance,
>> it could try to migrate mlocked pages without retrial.
>>
>>
>> Below is the issue of CMA_ALLOC of large size buffer : (Kernel version -
>> 4.14.65 (On Android pie [ARM])).
>>
>> [ 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
>>
>>
>> Below is the patch which solved this issue :
>>
>> diff --git a/mm/vmscan.c b/mm/vmscan.c
>> index be56e2e..12ac353 100644
>> --- a/mm/vmscan.c
>> +++ b/mm/vmscan.c
>> @@ -998,7 +998,7 @@ static unsigned long shrink_page_list(struct list_head
>> *page_list,
>> sc->nr_scanned++;
>>
>> if (unlikely(!page_evictable(page)))
>> - goto activate_locked;
>> + goto cull_mlocked;
>>
>> if (!sc->may_unmap && page_mapped(page))
>> goto keep_locked;
>> @@ -1331,7 +1331,12 @@ 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. */
>> if (PageSwapCache(page) && (mem_cgroup_swap_full(page) ||
>>
>>
>>
>>
>> It fixes the below issue.
>>
>> 1. Large size buffer allocation using cma_alloc successful with unevictable
>> pages.
>>
>> cma_alloc of current kernel will fail due to unevictable page
>>
>> Please let me know if anything i am missing.
>>
>> Regards,
>> Pankaj
>>
>> From: Vlastimil Babka <vba...@suse.cz>
>> Sent: 18 March 2019 14:12:50
>> To: Pankaj Suryawanshi; Kirill Tkhai; Michal Hocko;
>> aneesh.ku...@linux.ibm.com
>> Cc: linux-kernel@vger.kernel.org; minc...@kernel.org; linux...@kvack.org;
>> khand...@linux.vnet.ibm.com; hillf...@alibaba-inc.com
>> Subject: Re: [External] Re: vmscan: Reclaim unevictable pages
>>
>>
>> On 3/15/19 11:11 AM, Pankaj Suryawanshi wrote:
>>>
>>> [ cc Aneesh kumar, Anshuman, Hillf, Vlastimil]
>>
>> Can you send a proper patch with changelog explaining the change? I
>> don't know the context of this thread.
>>
>>> From: Pankaj Suryawanshi
>>> Sent: 15 March 2019 11:35:05
>>> To: Kirill Tkhai; Michal Hocko
>>> Cc: linux-kernel@vger.kernel.org; minc...@kernel.org; linux...@kvack.org
>>> Subject: Re: Re: [External] Re: vmscan: Reclaim unevictable pages
>>>
>>>
>>>
>>> [ cc linux-mm ]
>>>
>>>
>>> From: Pankaj Suryawanshi
>>> Sent: 14 March 2019 19:14:40
>>> To: Kirill Tkhai; Michal Hocko
>>> Cc: linux-kernel@vger.kernel.org; minc...@kernel.org
>>> Subject: Re: Re: [External] Re: vmscan: Reclaim unevictable pages
>>>
>>>
>>>
>>> Hello ,
>>>
>>> Please ignore the curly braces, they are just for debugging.
>>>
>>> Below is the updated patch.
>>>
>>>
>>> diff --git a/mm/vmscan.c b/mm/vmscan.c
>>> index be56e2e..12ac353 100644
>>> --- a/mm/vmscan.c
>>> +++ b/mm/vmscan.c
>>> @@ -998,7 +998,7 @@ static unsigned long shrink_page_list(struct list_head
>>> *page_list,
>>> sc->nr_scanned++;
>>>
>>> if (unlikely(!page_evictable(page)))
>>> - goto activate_locked;
>>> + goto cull_mlocked;
>>>
>>> if (!sc->may_unmap && page_mapped(page))
>>> goto keep_locked;
>>> @@ -1331,7 +1331,12 @@ 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. */
>>> if (PageSwapCache(page) && (mem_cgroup_swap_full(page) ||
>>>
>>>
>>>
>>> Regards,
>>> Pankaj
>>>
>>>
>>> From: Kirill Tkhai <ktk...@virtuozzo.com>
>>> Sent: 14 March 2019 14:55:34
>>> To: Pankaj Suryawanshi; Michal Hocko
>>> Cc: linux-kernel@vger.kernel.org; minc...@kernel.org
>>> Subject: Re: Re: [External] Re: vmscan: Reclaim unevictable pages
>>>
>>>
>>> On 14.03.2019 11:52, Pankaj Suryawanshi wrote:
>>>>
>>>> I am using kernel version 4.14.65 (on Android pie [ARM]).
>>>>
>>>> No additional patches applied on top of vanilla.(Core MM).
>>>>
>>>> If I change in the vmscan.c as below patch, it will work.
>>>
>>> Sorry, but 4.14.65 does not have braces around trylock_page(),
>>> like in your patch below.
>>>
>>> See
>>> https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/mm/vmscan.c?h=v4.14.65
>>>
>>> [...]
>>>
>>>>> 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;
>>>>> }
>>>
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>>
>>
>>
>
>
