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Subject: RE: [PATCH] dma-buf/heaps: c9e8440eca61 staging: ion: Fix overflow
 and list bugs in system heap:
Reply-To: jaewon31.kim@samsung.com
Sender: Jaewon Kim <jaewon31.kim@samsung.com>
From:   Jaewon Kim <jaewon31.kim@samsung.com>
To:     "T.J. Mercier" <tjmercier@google.com>
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Date:   Thu, 30 Mar 2023 09:41:17 +0900
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>On Tue, Mar 28, 2023 at 8:13?PM Jaewon Kim <jaewon31.kim@samsung.com> wrote:
>>
>> >On Tue, Mar 28, 2023 at 5:58?AM Jaewon Kim <jaewon31.kim@samsung.com> wrote:
>> >>
>> >> Normal free:212600kB min:7664kB low:57100kB high:106536kB
>> >>   reserved_highatomic:4096KB active_anon:276kB inactive_anon:180kB
>> >>   active_file:1200kB inactive_file:0kB unevictable:2932kB
>> >>   writepending:0kB present:4109312kB managed:3689488kB mlocked:2932kB
>> >>   pagetables:13600kB bounce:0kB free_pcp:0kB local_pcp:0kB
>> >>   free_cma:200844kB
>> >> Out of memory and no killable processes...
>> >> Kernel panic - not syncing: System is deadlocked on memory
>> >>
>> >> An OoM panic was reported, there were only native processes which are
>> >> non-killable as OOM_SCORE_ADJ_MIN.
>> >>
>> >> After looking into the dump, I've found the dma-buf system heap was
>> >> trying to allocate a huge size. It seems to be a signed negative value.
>> >>
>> >> dma_heap_ioctl_allocate(inline)
>> >>     |  heap_allocation = 0xFFFFFFC02247BD38 -> (
>> >>     |    len = 0xFFFFFFFFE7225100,
>> >>
>> >> Actually the old ion system heap had policy which does not allow that
>> >> huge size with commit c9e8440eca61 ("staging: ion: Fix overflow and list
>> >> bugs in system heap"). We need this change again. Single allocation
>> >> should not be bigger than half of all memory.
>> >>
>> >> Signed-off-by: Jaewon Kim <jaewon31.kim@samsung.com>
>> >> ---
>> >>  drivers/dma-buf/heaps/system_heap.c | 3 +++
>> >>  1 file changed, 3 insertions(+)
>> >>
>> >> diff --git a/drivers/dma-buf/heaps/system_heap.c b/drivers/dma-buf/heaps/system_heap.c
>> >> index e8bd10e60998..4c1ef2ecfb0f 100644
>> >> --- a/drivers/dma-buf/heaps/system_heap.c
>> >> +++ b/drivers/dma-buf/heaps/system_heap.c
>> >> @@ -351,6 +351,9 @@ static struct dma_buf *system_heap_allocate(struct dma_heap *heap,
>> >>         struct page *page, *tmp_page;
>> >>         int i, ret = -ENOMEM;
>> >>
>> >> +       if (len / PAGE_SIZE > totalram_pages() / 2)
>> >> +               return ERR_PTR(-ENOMEM);
>> >> +
>> >
>> >Instead of policy like that, would __GFP_RETRY_MAYFAIL on the system
>> >heap's LOW_ORDER_GFP flags also avoid the panic, and eventually fail
>> >the allocation request?
>>
>> Hello T.J.
>>
>> Thank you for your opinion.
>> The __GFP_RETRY_MAYFAIL on LOW_ORDER_GFP seems to work.
>>
>> page allocation failure: order:0, mode:0x144dc2(GFP_HIGHUSER|__GFP_RETRY_MAYFAIL|__GFP_COMP|__GFP_ZERO)
>> Node 0 active_anon:120kB inactive_anon:43012kB active_file:36kB inactive_file:788kB
>>
>> I tried to test it, and the allocation stopped at very low file cache situation without OoM panic
>> as we expected. The phone device was freezing for few seconds though.
>>
>> We can avoid OoM panic through either totalram_pages() / 2 check or __GFP_RETRY_MAYFAIL.
>>
>> But I think we still need the totalram_pages() / 2 check so that we don't have to suffer
>> the freezing in UX perspective. We may kill some critical processes or users' recent apps.
>>
>> Regarding __GFP_RETRY_MAYFAIL, I think it will help us avoid OoM panic. But I'm worried
>> about low memory devices which still need OoM kill to get memory like in camera scenarios.
>>
>> So what do you think?
>>
>Hey Jaewon, thanks for checking! The totalram_pages() / 2 just feels
>somewhat arbitrary. On the lowest memory devices I'm aware of that use
>the system heap it would take a single buffer on the order of several
>hundred megabytes to exceed that, so I guess the simple check is fine
>here until someone says they just can't live without a buffer that
>big!
>
>Reviewed-by: T.J. Mercier <tjmercier@google.com>

Hello T.J.

Thank you for your Reviewed-by.

I also think the totalram_pages() / 2 doesn't look perfect, but I think
we need it.

By the way I'm a little confused on a single buffer. Please help me to be clear.
Do you mean we may need to reconsider the totalram_pages() / 2 some day, 
if camera may request a huge memory for a single camera buffer? Then I hope
the device has also huge total memory to support that high quality camera.

And if possible, could you give your idea about __GFP_RETRY_MAYFAIL regarding
what I said? I think OoM kill doesn't seem to occur that often thanks to LMKD kill. 
And I also want to avoid OoM panic, so I'd like to apply it.
But what if there is a situation which still need OoM kill to get memory. I just
thought policy of __GFP_RETRY_MAYFAIL could be changed to allow OoM kill but return
NULL when there was a victim process.

Thank you
Jaewon Kim