[PATCH v4 9/9] RDMA/umem_odp: optimize out the case when a range is updated to read only

[jglisse]

From: JÃrÃme Glisse <jglisse@xxxxxxxxxx>

When range of virtual address is updated read only and corresponding
user ptr object are already read only it is pointless to do anything.
Optimize this case out.

Signed-off-by: JÃrÃme Glisse <jglisse@xxxxxxxxxx>
Cc: Christian KÃnig <christian.koenig@xxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Felix Kuehling <Felix.Kuehling@xxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
Cc: Ross Zwisler <zwisler@xxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Cc: Radim KrÄmÃÅ <rkrcmar@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Ralph Campbell <rcampbell@xxxxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: kvm@xxxxxxxxxxxxxxx
Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx
Cc: linux-rdma@xxxxxxxxxxxxxxx
Cc: linux-fsdevel@xxxxxxxxxxxxxxx
Cc: Arnd Bergmann <arnd@xxxxxxxx>
---
 drivers/infiniband/core/umem_odp.c | 22 +++++++++++++++++++---
 include/rdma/ib_umem_odp.h         |  1 +
 2 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/drivers/infiniband/core/umem_odp.c b/drivers/infiniband/core/umem_odp.c
index a4ec43093cb3..fa4e7fdcabfc 100644
--- a/drivers/infiniband/core/umem_odp.c
+++ b/drivers/infiniband/core/umem_odp.c
@@ -140,8 +140,15 @@ static void ib_umem_notifier_release(struct mmu_notifier *mn,
 static int invalidate_range_start_trampoline(struct ib_umem_odp *item,
 					     u64 start, u64 end, void *cookie)
 {
+	bool update_to_read_only = *((bool *)cookie);
+
 	ib_umem_notifier_start_account(item);
-	item->umem.context->invalidate_range(item, start, end);
+	/*
+	 * If it is already read only and we are updating to read only then we
+	 * do not need to change anything. So save time and skip this one.
+	 */
+	if (!update_to_read_only || !item->read_only)
+		item->umem.context->invalidate_range(item, start, end);
 	return 0;
 }
 
@@ -150,6 +157,7 @@ static int ib_umem_notifier_invalidate_range_start(struct mmu_notifier *mn,
 {
 	struct ib_ucontext_per_mm *per_mm =
 		container_of(mn, struct ib_ucontext_per_mm, mn);
+	bool update_to_read_only;
 
 	if (range->blockable)
 		down_read(&per_mm->umem_rwsem);
@@ -166,10 +174,13 @@ static int ib_umem_notifier_invalidate_range_start(struct mmu_notifier *mn,
 		return 0;
 	}
 
+	update_to_read_only = mmu_notifier_range_update_to_read_only(range);
+
 	return rbt_ib_umem_for_each_in_range(&per_mm->umem_tree, range->start,
 					     range->end,
 					     invalidate_range_start_trampoline,
-					     range->blockable, NULL);
+					     range->blockable,
+					     &update_to_read_only);
 }
 
 static int invalidate_range_end_trampoline(struct ib_umem_odp *item, u64 start,
@@ -363,6 +374,9 @@ struct ib_umem_odp *ib_alloc_odp_umem(struct ib_ucontext_per_mm *per_mm,
 		goto out_odp_data;
 	}
 
+	/* Assume read only at first, each time GUP is call this is updated. */
+	odp_data->read_only = true;
+
 	odp_data->dma_list =
 		vzalloc(array_size(pages, sizeof(*odp_data->dma_list)));
 	if (!odp_data->dma_list) {
@@ -619,8 +633,10 @@ int ib_umem_odp_map_dma_pages(struct ib_umem_odp *umem_odp, u64 user_virt,
 		goto out_put_task;
 	}
 
-	if (access_mask & ODP_WRITE_ALLOWED_BIT)
+	if (access_mask & ODP_WRITE_ALLOWED_BIT) {
+		umem_odp->read_only = false;
 		flags |= FOLL_WRITE;
+	}
 
 	start_idx = (user_virt - ib_umem_start(umem)) >> page_shift;
 	k = start_idx;
diff --git a/include/rdma/ib_umem_odp.h b/include/rdma/ib_umem_odp.h
index 0b1446fe2fab..8256668c6170 100644
--- a/include/rdma/ib_umem_odp.h
+++ b/include/rdma/ib_umem_odp.h
@@ -76,6 +76,7 @@ struct ib_umem_odp {
 	struct completion	notifier_completion;
 	int			dying;
 	struct work_struct	work;
+	bool read_only;
 };
 
 static inline struct ib_umem_odp *to_ib_umem_odp(struct ib_umem *umem)
-- 
2.17.2