2020년 7월 9일 (목) 오후 3:43, Michal Hocko <mho...@kernel.org>님이 작성:
>
> On Wed 08-07-20 09:41:06, Michal Hocko wrote:
> > On Wed 08-07-20 16:16:02, Joonsoo Kim wrote:
> > > On Tue, Jul 07, 2020 at 01:22:31PM +0200, Vlastimil Babka wrote:
> > > > On 7/7/20 9:44 AM, js1...@gmail.com wrote:
> > > > > From: Joonsoo Kim <iamjoonsoo....@lge.com>
> > > > >
> > > > > new_non_cma_page() in gup.c which try to allocate migration target
> > > > > page
> > > > > requires to allocate the new page that is not on the CMA area.
> > > > > new_non_cma_page() implements it by removing __GFP_MOVABLE flag.
> > > > > This way
> > > > > works well for THP page or normal page but not for hugetlb page.
> > > > >
> > > > > hugetlb page allocation process consists of two steps. First is
> > > > > dequeing
> > > > > from the pool. Second is, if there is no available page on the queue,
> > > > > allocating from the page allocator.
> > > > >
> > > > > new_non_cma_page() can control allocation from the page allocator by
> > > > > specifying correct gfp flag. However, dequeing cannot be controlled
> > > > > until
> > > > > now, so, new_non_cma_page() skips dequeing completely. It is a
> > > > > suboptimal
> > > > > since new_non_cma_page() cannot utilize hugetlb pages on the queue so
> > > > > this
> > > > > patch tries to fix this situation.
> > > > >
> > > > > This patch makes the deque function on hugetlb CMA aware and skip CMA
> > > > > pages if newly added skip_cma argument is passed as true.
> > > >
> > > > Hmm, can't you instead change dequeue_huge_page_node_exact() to test
> > > > the PF_
> > > > flag and avoid adding bool skip_cma everywhere?
> > >
> > > Okay! Please check following patch.
> > > >
> > > > I think that's what Michal suggested [1] except he said "the code
> > > > already does
> > > > by memalloc_nocma_{save,restore} API". It needs extending a bit though,
> > > > AFAICS.
> > > > __gup_longterm_locked() indeed does the save/restore, but restore comes
> > > > before
> > > > check_and_migrate_cma_pages() and thus new_non_cma_page() is called, so
> > > > an
> > > > adjustment is needed there, but that's all?
> > > >
> > > > Hm the adjustment should be also done because save/restore is done
> > > > around
> > > > __get_user_pages_locked(), but check_and_migrate_cma_pages() also calls
> > > > __get_user_pages_locked(), and that call not being between nocma save
> > > > and
> > > > restore is thus also a correctness issue?
> > >
> > > Simply, I call memalloc_nocma_{save,restore} in new_non_cma_page(). It
> > > would not cause any problem.
> >
> > I believe a proper fix is the following. The scope is really defined for
> > FOLL_LONGTERM pins and pushing it inside check_and_migrate_cma_pages
> > will solve the problem as well but it imho makes more sense to do it in
> > the caller the same way we do for any others.
> >
> > Fixes: 9a4e9f3b2d73 ("mm: update get_user_pages_longterm to migrate pages
> > allocated from CMA region")
> >
> > I am not sure this is worth backporting to stable yet.
>
> Should I post it as a separate patch do you plan to include this into your
> next version?
It's better to include it on my next version since this patch would
cause a conflict with
the next tree that includes my v3 of this patchset.
Thanks.
