Re: [PATCH v3 1/5] mm: introduce MADV_COLD

[Michal Hocko]

On Thu 27-06-19 06:13:36, Dave Hansen wrote:
> On 6/27/19 4:54 AM, Minchan Kim wrote:
> > This patch introduces the new MADV_COLD hint to madvise(2) syscall.
> > MADV_COLD can be used by a process to mark a memory range as not expected
> > to be used in the near future. The hint can help kernel in deciding which
> > pages to evict early during memory pressure.
> > 
> > It works for every LRU pages like MADV_[DONTNEED|FREE]. IOW, It moves
> > 
> > 	active file page -> inactive file LRU
> > 	active anon page -> inacdtive anon LRU
> 
> Is the LRU behavior part of the interface or the implementation?
> 
> I ask because we've got something in between tossing something down the
> LRU and swapping it: page migration.  Specifically, on a system with
> slower memory media (like persistent memory) we just migrate a page
> instead of discarding it at reclaim:

But we already do have interfaces for migrating the memory
(move_pages(2)). Why should this interface duplicate that interface?
I believe the only purpose of these two new madvise modes is to provide
a non-destructive MADV_{DONTNEED,FREE} alteternatives. In other words,
pageout vs. age interface.
-- 
Michal Hocko
SUSE Labs