Re: [PATCH 1/1] infiniband/mm: convert put_page() to put_user_page*()

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On 5/23/19 10:32 AM, Jason Gunthorpe wrote:
On Thu, May 23, 2019 at 10:28:52AM -0700, Ira Weiny wrote:
@@ -686,8 +686,8 @@ int ib_umem_odp_map_dma_pages(struct ib_umem_odp *umem_odp, u64 user_virt,
  			 * ib_umem_odp_map_dma_single_page().
  			 */
  			if (npages - (j + 1) > 0)
-				release_pages(&local_page_list[j+1],
-					      npages - (j + 1));
+				put_user_pages(&local_page_list[j+1],
+					       npages - (j + 1));

I don't know if we discussed this before but it looks like the use of
release_pages() was not entirely correct (or at least not necessary) here.  So
I think this is ok.

Oh? John switched it from a put_pages loop to release_pages() here:

commit 75a3e6a3c129cddcc683538d8702c6ef998ec589
Author: John Hubbard <jhubbard@xxxxxxxxxx>
Date:   Mon Mar 4 11:46:45 2019 -0800

     RDMA/umem: minor bug fix in error handling path
1. Bug fix: fix an off by one error in the code that cleans up if it fails
        to dma-map a page, after having done a get_user_pages_remote() on a
        range of pages.
2. Refinement: for that same cleanup code, release_pages() is better than
        put_page() in a loop.
And now we are going to back something called put_pages() that
implements the same for loop the above removed?

Seems like we are going in circles?? John?


put_user_pages() is meant to be a drop-in replacement for release_pages(),
so I made the above change as an interim step in moving the callsite from
a loop, to a single call.

And at some point, it may be possible to find a way to optimize put_user_pages()
in a similar way to the batching that release_pages() does, that was part
of the plan for this.

But I do see what you mean: in the interim, maybe put_user_pages() should
just be calling release_pages(), how does that change sound?


thanks,
--
John Hubbard
NVIDIA



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