Re: A question about the patch(commit :c777e2a8b654 powerpc/mm: Fix Multi hit ERAT cause by recent THP update)

[Michal Hocko <mhocko@kernel.org>]

On Thu 23-06-16 11:29:46, Michal Hocko wrote:
> On Wed 22-06-16 23:05:24, zhong jiang wrote:
> > Hi  Aneesh
> > 
> >                 CPU0                            CPU1
> >     shrink_page_list()
> >       add_to_swap()
> >         split_huge_page_to_list()
> >           __split_huge_pmd_locked()
> >             pmdp_huge_clear_flush_notify()
> >         // pmd_none() == true
> >                                         exit_mmap()
> >                                           unmap_vmas()
> >                                             zap_pmd_range()
> >                                               // no action on pmd since pmd_none() == true
> >         pmd_populate()
> > 
> > 
> > the mm should be the last user  when CPU1 process is exiting,  CPU0 must be a own mm .
> > two different process  should not be influenced each other.  in a words , they should not
> > have race.
> 
> No this is a different scenario than
> http://lkml.kernel.org/r/1466517956-13875-1-git-send-email-zhongjiang@huawei.com
> we were discussing recently. Note that pages are still on the LRU lists
> while the mm which maps them is exiting. So the above race is very much
> possible.

And just to clarify, I haven't checked the current code after c777e2a8b654
("powerpc/mm: Fix Multi hit ERAT cause by recent THP update") which is
ppc specific and I have no idea whether other arches need a similar
treatment. I was merely trying to explain that the mm exclusive argument
doesn't apply to reclaim vs. exit races.
-- 
Michal Hocko
SUSE Labs

--
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>