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.
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: Pankaj Suryawanshi
Sent: 18 March 2019 13:15:22
To: Kirill Tkhai; Michal Hocko; aneesh.kumar@xxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx; minchan@xxxxxxxxxx; linux-mm@xxxxxxxxx; khandual@xxxxxxxxxxxxxxxxxx; vbabka@xxxxxxx
Subject: Re: Re: [External] Re: vmscan: Reclaim unevictable pages
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 pages.
Solved the below issue of cma_alloc
-----------------------------------------------------------------------------------------------------------------------------------------
[ 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
-----------------------------------------------------------------------------------------------------------------------------------------
From: Pankaj Suryawanshi
Sent: 15 March 2019 15:41:57
To: Kirill Tkhai; Michal Hocko; aneesh.kumar@xxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx; minchan@xxxxxxxxxx; linux-mm@xxxxxxxxx; khandual@xxxxxxxxxxxxxxxxxx; hillf.zj@xxxxxxxxxxxxxxx; vbabka@xxxxxxx
Subject: Re: Re: [External] Re: vmscan: Reclaim unevictable pages
[ cc Aneesh kumar, Anshuman, Hillf, Vlastimil]
From: Pankaj Suryawanshi
Sent: 15 March 2019 11:35:05
To: Kirill Tkhai; Michal Hocko
Cc: linux-kernel@xxxxxxxxxxxxxxx; minchan@xxxxxxxxxx; linux-mm@xxxxxxxxx
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@xxxxxxxxxxxxxxx; minchan@xxxxxxxxxx
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 <ktkhai@xxxxxxxxxxxxx>
Sent: 14 March 2019 14:55:34
To: Pankaj Suryawanshi; Michal Hocko
Cc: linux-kernel@xxxxxxxxxxxxxxx; minchan@xxxxxxxxxx
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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