Re: [RFC] Hugepage collapse in process context

[Alex Shi <alex.shi@linux.alibaba.com>]

在 2021/3/2 上午4:56, David Rientjes 写道:
> On Wed, 24 Feb 2021, Alex Shi wrote:
> 
>>> Agreed, and happy to see that there's a general consensus for the 
>>> direction.  Benefit of a new madvise mode is that it can be used for 
>>> madvise() as well if you are interested in only a single range of your own 
>>> memory and then it doesn't need to reconcile with any of the already 
>>> overloaded semantics of MADV_HUGEPAGE.
>>
>> It's a good idea to let process deal with its own THP policy.
>> but current applications will miss the benefit w/o changes, and change is
>> expensive for end users. So except this work, may a per memcg collapse benefit
>> apps and free for them, we often deploy apps in cgroups on server now.
>>
> 
> Hi Alex,
> 
> I'm not sure that I understand: this MADV_COLLAPSE would be possible for 
> process_madvise() as well and by passing a vectored set of ranges so a 
> process can do this on behalf of other processes (it's the only way that 
> we could theoretically move khugepaged to userspace, although that's not 
> an explicit end goal).
> 

Forgive my stupidity, I still can't figure out how process_madvise caller
fill the iovec of other's on a common system. 

> 
> How would you see this working with memcg involved?  I had thought this 
> was entirely orthogonal to any cgroup.
> 

You'r right, it's out of cgroup and better. per cgroup khugepaged could be
a alternative way. but it require a cgroup and not specific on target process.

Thanks
Alex