Re: [PATCH] mm: remove redundant check in handle_mm_fault

[Haifeng Xu]

On 2023/3/7 10:48, Matthew Wilcox wrote:
> On Tue, Mar 07, 2023 at 10:36:55AM +0800, Haifeng Xu wrote:
>> On 2023/3/6 21:49, David Hildenbrand wrote:
>>> On 06.03.23 03:49, Haifeng Xu wrote:
>>>> mem_cgroup_oom_synchronize() has checked whether current memcg_in_oom is
>>>> set or not, so remove the check in handle_mm_fault().
>>>
>>> "mem_cgroup_oom_synchronize() will returned immediately if memcg_in_oom is not set, so remove the check from handle_mm_fault()".
>>>
>>> However, that requires now always an indirect function call -- do we care about dropping that optimization?
>>>
>>>
>>
>> If memcg_in_oom is set, we will check it twice, one is from handle_mm_fault(), the other is from mem_cgroup_oom_synchronize(). That seems a bit redundant.
>>
>> if memcg_in_oom is not set, mem_cgroup_oom_synchronize() returns directly. Though it's an indirect function call, but the time spent can be negligible 
>> compare to the whole mm user falut preocess. And that won't cause stack overflow error.
> 
> I suggest you measure it.

Ok, I'll make a simple test.