On 2/4/21 12:15 AM, John Hubbard wrote:

On 2/3/21 2:00 PM, Joao Martins wrote:

quoted

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:

In the patch subject line:

    s/__ib_mem_release/__ib_umem_release/

Ah, yes.

quoted

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

After:
2631 rounds in 5.001 sec: 1900.618 usec / round
31625 rounds in 60.001 sec: 1897.267 usec / round

Signed-off-by: Joao Martins <redacted>
---
  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..ea4ebb3261d9 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;
+	int i;

Maybe unsigned int is better, so as to perfectly match the scatterlist.length.

Will fix.

quoted

  
  	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->nmap, i)

The change from umem->sg_nents to umem->nmap looks OK, although we should get
IB people to verify that there is not some odd bug or reason to leave it as is.

/me nods

fwiw this was suggested by Jason :) as the way I had done was unnecessarily allocating a
page to unpin pages.

quoted

+		unpin_user_page_range_dirty_lock(sg_page(sg),
+			DIV_ROUND_UP(sg->length, PAGE_SIZE), make_dirty);

Is it really OK to refer directly to sg->length? The scatterlist library goes
to some effort to avoid having callers directly access the struct member variables.

Actually, the for_each_sg() code and its behavior with sg->length and sg_page(sg)
confuses me because I'm new to it, and I don't quite understand how this works.

So IIUC this can be done given how ib_umem_get allocates scatterlists (i.e. see the call
to __sg_alloc_table_from_pages()). It builds a scatterlist with a segment size in device
DMA max segment size  (e.g. 64K, 2G or etc depending on what the device sets it to) and
after created each scatterlist I am iterating represents a contiguous range of PFNs with a
starting page. And if you keep pinning contiguous amounts of memory, it keeps coalescing
this to the previously allocated sgl.

Especially with SG_CHAIN. I'm assuming that you've monitored /proc/vmstat for
nr_foll_pin* ?

Yeap I did. I see no pages left unpinned.

quoted

  
  	sg_free_table(&umem->sg_head);
  }

thanks,