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SubjectRe: [PATCH 2/3] mm/gup: Introduce get_user_pages_fast_longterm()
On Mon, Feb 11, 2019 at 01:39:12PM -0800, John Hubbard wrote:
> On 2/11/19 1:26 PM, Ira Weiny wrote:
> > On Mon, Feb 11, 2019 at 01:13:56PM -0800, John Hubbard wrote:
> >> On 2/11/19 12:39 PM, Jason Gunthorpe wrote:
> >>> On Mon, Feb 11, 2019 at 12:16:42PM -0800, ira.weiny@intel.com wrote:
> >>>> From: Ira Weiny <ira.weiny@intel.com>
> >> [...]
> >> It seems to me that the longterm vs. short-term is of questionable value.
> >
> > This is exactly why I did not post this before. I've been waiting our other
> > discussions on how GUP pins are going to be handled to play out. But with the
> > netdev thread today[1] it seems like we need to make sure we have a "safe" fast
> > variant for a while. Introducing FOLL_LONGTERM seemed like the cleanest way to
> > do that even if we will not need the distinction in the future... :-(
>
> Yes, I agree. Below...
>
> > [...]
> > This is also why I did not change the get_user_pages_longterm because we could
> > be ripping this all out by the end of the year... (I hope. :-)
> >
> > So while this does "pollute" the GUP family of calls I'm hoping it is not
> > forever.
> >
> > Ira
> >
> > [1] https://lkml.org/lkml/2019/2/11/1789
> >
>
> Yes, and to be clear, I think your patchset here is fine. It is easy to find
> the FOLL_LONGTERM callers if and when we want to change anything. I just think
> also it's appopriate to go a bit further, and use FOLL_LONGTERM all by itself.
>
> That's because in either design outcome, it's better that way:
>
> -- If we keep the concept of "I'm a long-term gup call site", then FOLL_LONGTERM
> is just right. The gup API already has _fast and non-fast variants, and once
> you get past a couple, you end up with a multiplication of names that really
> work better as flags. We're there.
>
> -- If we drop the concept, then you've already done part of the work, by removing
> the _longterm API variants.

Fair enough. But to do that correctly I think we will need to convert
get_user_pages_fast() to use flags as well. I have a version of this series
which includes a patch does this, but the patch touched a lot of subsystems and
a couple of different architectures...[1]

I can't test them all. If we want to go that way I'm up for submitting the
patch... But if we remove longterm in the future we may be left with a
get_user_pages_fast() which really only needs 1 flag. But perhaps overall we
would be better off?

Ira


[1] mm/gup.c: Change GUP fast to use flags rather than write bool

To facilitate additional options to get_user_pages_fast change the
singular write parameter to be the more generic gup_flags.

This patch currently does not change any functionality. New
functionality will follow in subsequent patches.

Many of the get_user_pages_fast call sites were unchanged because they
already used FOLL_WRITE or 0 as appropriate.

Signed-off-by: Ira Weiny <ira.weiny@intel.com>
---
arch/mips/mm/gup.c | 11 ++++++-----
arch/powerpc/kvm/book3s_64_mmu_hv.c | 4 ++--
arch/powerpc/kvm/e500_mmu.c | 2 +-
arch/powerpc/mm/mmu_context_iommu.c | 4 ++--
arch/s390/kvm/interrupt.c | 2 +-
arch/s390/mm/gup.c | 12 ++++++------
arch/sh/mm/gup.c | 11 ++++++-----
arch/sparc/mm/gup.c | 9 +++++----
arch/x86/kvm/paging_tmpl.h | 2 +-
arch/x86/kvm/svm.c | 2 +-
drivers/fpga/dfl-afu-dma-region.c | 2 +-
drivers/gpu/drm/via/via_dmablit.c | 3 ++-
drivers/infiniband/hw/hfi1/user_pages.c | 3 ++-
drivers/misc/genwqe/card_utils.c | 2 +-
drivers/misc/vmw_vmci/vmci_host.c | 2 +-
drivers/misc/vmw_vmci/vmci_queue_pair.c | 6 ++++--
drivers/platform/goldfish/goldfish_pipe.c | 3 ++-
drivers/rapidio/devices/rio_mport_cdev.c | 4 +++-
drivers/sbus/char/oradax.c | 2 +-
drivers/scsi/st.c | 3 ++-
drivers/staging/gasket/gasket_page_table.c | 4 ++--
drivers/tee/tee_shm.c | 2 +-
drivers/vfio/vfio_iommu_spapr_tce.c | 3 ++-
drivers/vhost/vhost.c | 2 +-
drivers/video/fbdev/pvr2fb.c | 2 +-
drivers/virt/fsl_hypervisor.c | 2 +-
drivers/xen/gntdev.c | 2 +-
fs/orangefs/orangefs-bufmap.c | 2 +-
include/linux/mm.h | 4 ++--
kernel/futex.c | 2 +-
lib/iov_iter.c | 7 +++++--
mm/gup.c | 10 +++++-----
mm/util.c | 8 ++++----
net/ceph/pagevec.c | 2 +-
net/rds/info.c | 2 +-
net/rds/rdma.c | 3 ++-
36 files changed, 81 insertions(+), 65 deletions(-)


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