On 2016/7/28 15:58, Michal Hocko wrote:

On Thu 28-07-16 15:41:53, Xishi Qiu wrote:

quoted

On 2016/7/28 15:20, Michal Hocko wrote:

quoted

On Thu 28-07-16 15:08:26, Xishi Qiu wrote:

quoted

Usually THREAD_SIZE_ORDER is 2, it means we need to alloc 16kb continuous
physical memory during fork a new process.

If the system's memory is very small, especially the smart phone, maybe there
is only 1G memory. So the free memory is very small and compaction is not
always success in slowpath(__alloc_pages_slowpath), then alloc thread stack
may be failed for memory fragment.

Well, with the current implementation of the page allocator those
requests will not fail in most cases. The oom killer would be invoked in
order to free up some memory.

Hi Michal,

Yes, it success in most cases, but I did have seen this problem in some
stress-test.

DMA free:470628kB, but alloc 2 order block failed during fork a new process.
There are so many memory fragments and the large block may be soon taken by
others after compact because of stress-test.

--- dmesg messages ---

07-13 08:41:51.341 <4>[309805.658142s][pid:1361,cpu5,sManagerService]sManagerService: page allocation failure: order:2, mode:0x2000d1

Yes but this is __GFP_DMA allocation. I guess you have already reported
this failure and you've been told that this is quite unexpected for the
kernel stack allocation. It is your out-of-tree patch which just makes
things worse because DMA restricted allocations are considered "lowmem"
and so they do not invoke OOM killer and do not retry like regular
GFP_KERNEL allocations.

Hi Michal,

Yes, we add GFP_DMA, but I don't think this is the key for the problem.

If we do oom-killer, maybe we will get a large block later, but there
is enough free memory before oom(although most of them are fragments).

I wonder if we can alloc success without kill any process in this situation.
Maybe use vmalloc is a good way, but I don't know the influence.

Thanks,
Xishi Qiu

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>