On 03/13/2015 07:18 PM, David Rientjes wrote:
> On Fri, 13 Mar 2015, Eric B Munson wrote:
>
>>>> --- a/mm/compaction.c
>>>> +++ b/mm/compaction.c
>>>> @@ -1046,6 +1046,8 @@ typedef enum {
>>>> ISOLATE_SUCCESS, /* Pages isolated, migrate */
>>>> } isolate_migrate_t;
>>>>
>>>> +int sysctl_compact_unevictable;
>>>> +
>>>> /*
>>>> * Isolate all pages that can be migrated from the first suitable block,
>>>> * starting at the block pointed to by the migrate scanner pfn within
>>>
>>> I suspect that the use cases where users absolutely do not want
>>> unevictable pages migrated are special cases, and it may make
>>> sense to enable sysctl_compact_unevictable by default.
>>
>> Given that sysctl_compact_unevictable=0 is the way the kernel behaves
>> now and the push back against always enabling compaction on unevictable
>> pages, I left the default to be the behavior as it is today. I agree
>> that this is likely the minority case, but I'd really like Peter Z or
>> someone else from real time to say that they are okay with the default
>> changing.
>>
>
> It would be really disappointing to not enable this by default for !rt
> kernels. We haven't migrated mlocked pages in the past by way of memory
> compaction because it can theoretically result in consistent minor page
> faults, but I haven't yet heard a !rt objection to enabling this.
>
> If the rt patchset is going to carry a patch to disable this
It does not have to carry a patch to disable something that can be
disabled at run time.
The smaller the realtime patchset has to be, the better.
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