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From:   Pankaj Suryawanshi <pankaj.suryawanshi@einfochips.com>
To:     Kirill Tkhai <ktkhai@virtuozzo.com>,
        Michal Hocko <mhocko@kernel.org>,
        "aneesh.kumar@linux.ibm.com" <aneesh.kumar@linux.ibm.com>
CC:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "minchan@kernel.org" <minchan@kernel.org>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "khandual@linux.vnet.ibm.com" <khandual@linux.vnet.ibm.com>,
        "vbabka@suse.cz" <vbabka@suse.cz>
Subject: Re: vmscan: Reclaim unevictable pages
Thread-Topic: vmscan: Reclaim unevictable pages
Thread-Index: AQHU3Wh1dtxb99h/iUqWjmlP8cXYrA==
Date:   Mon, 18 Mar 2019 08:56:21 +0000
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Hello

shrink_page_list() returns , number of pages reclaimed, when pages is unevi=
ctable it returns VM_BUG_ON_PAGE(PageLRU(page) || PageUnevicatble(page),pag=
e);

We can add the unevictable pages in reclaim list in shrink_page_list(), ret=
urn total number of reclaim pages including unevictable pages, let the call=
er handle unevictable pages.

I think the problem is shrink_page_list is awkard. If page is unevictable i=
t goto activate_locked->keep_locked->keep lables, keep lable list_add the u=
nevictable 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) || PageUne=
victable(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_he=
ad *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@linux.ibm.com
Cc: linux-kernel@vger.kernel.org; minchan@kernel.org; linux-mm@kvack.org; k=
handual@linux.vnet.ibm.com; vbabka@suse.cz
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) || PageUn=
evictable(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@linux.ibm.com
Cc: linux-kernel@vger.kernel.org; minchan@kernel.org; linux-mm@kvack.org; k=
handual@linux.vnet.ibm.com; hillf.zj@alibaba-inc.com; vbabka@suse.cz
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@vger.kernel.org; minchan@kernel.org; linux-mm@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; minchan@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_he=
ad *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@virtuozzo.com>
Sent: 14 March 2019 14:55:34
To: Pankaj Suryawanshi; Michal Hocko
Cc: linux-kernel@vger.kernel.org; minchan@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=3Dv4.14.65

[...]

>> 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 =3D lru_to_page(page_list);
>>                  list_del(&page->lru);
>>
>>                 if (!trylock_page(page)) {
>>                          goto keep;
>>                 }

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