linux-kernel - [PATCH v2 4/4] RDMA/umem: batch page unpin in __ib_umem

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Date:   Thu,  4 Feb 2021 20:25:00 +0000
From:   Joao Martins <joao.m.martins@...cle.com>
To:     linux-mm@...ck.org
Cc:     linux-kernel@...r.kernel.org, linux-rdma@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Doug Ledford <dledford@...hat.com>,
        John Hubbard <jhubbard@...dia.com>,
        Matthew Wilcox <willy@...radead.org>,
        Joao Martins <joao.m.martins@...cle.com>
Subject: [PATCH v2 4/4] RDMA/umem: batch page unpin in __ib_umem_release()

Use the newly added unpin_user_page_range_dirty_lock()
for more quickly unpinning a consecutive range of pages
represented as compound pages. This will also calculate
number of pages to unpin (for the tail pages which matching
head page) and thus batch the refcount update.

Running a test program which calls mr reg/unreg on a 1G in size
and measures cost of both operations together (in a guest using rxe)
with THP and hugetlbfs:

Before:
590 rounds in 5.003 sec: 8480.335 usec / round
6898 rounds in 60.001 sec: 8698.367 usec / round

After:
2688 rounds in 5.002 sec: 1860.786 usec / round
32517 rounds in 60.001 sec: 1845.225 usec / round

Signed-off-by: Joao Martins <joao.m.martins@...cle.com>
---
 drivers/infiniband/core/umem.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/infiniband/core/umem.c b/drivers/infiniband/core/umem.c
index 2dde99a9ba07..9b607013e2a2 100644
--- a/drivers/infiniband/core/umem.c
+++ b/drivers/infiniband/core/umem.c
@@ -47,17 +47,17 @@
 
 static void __ib_umem_release(struct ib_device *dev, struct ib_umem *umem, int dirty)
 {
-	struct sg_page_iter sg_iter;
-	struct page *page;
+	bool make_dirty = umem->writable && dirty;
+	struct scatterlist *sg;
+	unsigned int i;
 
 	if (umem->nmap > 0)
 		ib_dma_unmap_sg(dev, umem->sg_head.sgl, umem->sg_nents,
 				DMA_BIDIRECTIONAL);
 
-	for_each_sg_page(umem->sg_head.sgl, &sg_iter, umem->sg_nents, 0) {
-		page = sg_page_iter_page(&sg_iter);
-		unpin_user_pages_dirty_lock(&page, 1, umem->writable && dirty);
-	}
+	for_each_sg(umem->sg_head.sgl, sg, umem->sg_nents, i)
+		unpin_user_page_range_dirty_lock(sg_page(sg),
+			DIV_ROUND_UP(sg->length, PAGE_SIZE), make_dirty);
 
 	sg_free_table(&umem->sg_head);
 }
-- 
2.17.1