On 12/8/18 4:42 AM, Andrew Morton wrote:
On Wed, 21 Nov 2018 14:52:56 +0530 "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxx> wrote:
Subject: [PATCH V4 0/3] * mm/kvm/vfio/ppc64: Migrate compound pages out of CMA region
Asterisk in title is strange?
My mistake while editing git-format-patch cover-letter.
ppc64 use CMA area for the allocation of guest page table (hash page table). We won't
be able to start guest if we fail to allocate hash page table. We have observed
hash table allocation failure because we failed to migrate pages out of CMA region
because they were pinned. This happen when we are using VFIO. VFIO on ppc64 pins
the entire guest RAM. If the guest RAM pages get allocated out of CMA region, we
won't be able to migrate those pages. The pages are also pinned for the lifetime of the
guest.
Currently we support migration of non-compound pages. With THP and with the addition of
hugetlb migration we can end up allocating compound pages from CMA region. This
patch series add support for migrating compound pages. The first path adds the helper
get_user_pages_cma_migrate() which pin the page making sure we migrate them out of
CMA region before incrementing the reference count.
Very little review activity. Perhaps Andrey and/or Michal can find the
time..
mm/migrate.c | 108 ++++++++++++++++++++++++++++++++++++++++
can we make this code disappear when CONFIG_CMA=n?
We can definitely do
static inline int get_user_pages_cma_migrate(unsigned long start, int
nr_pages, int write, struct page **pages)
{
return get_user_pages_fast(start, nr_pages, write, pages);
}
with #ifdef CONFIG_CMA around but that is unnecessary #ifdef in the
code. If CMA config is disabled, we will not be doing any migrate. Hence
wondering whether we need an alternative definition for CONFIG_CMA=n
-aneesh
