Messages in this thread | | | Subject | Re: [PATCH V4 0/3] * mm/kvm/vfio/ppc64: Migrate compound pages out of CMA region | From | "Aneesh Kumar K.V" <> | Date | Sat, 8 Dec 2018 22:34:39 +0530 |
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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@linux.ibm.com> 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
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