[PATCH v6 4/5] nfs: migrate direct I/O to iov_iter_extract_pages

[Pranjal Shrivastava <praan@google.com>]

Migrate the NFS Direct I/O path away from the legacy
iov_iter_get_pages_alloc2() API to the modern iov_iter_extract_pages API.
The transition aligns NFS with the modern VFS extraction model and serves
as a preparatory step for supporting requirements such as page pinning
via GUP for DMA.

The migration fixes a bug in the Direct I/O loop where pages were being
unpinned immediately after request creation. With the new extraction
model, pins are held until the I/O is complete. Manual release in the
loop is correspondingly updated to only clean up failed pages.

Signed-off-by: Pranjal Shrivastava <praan@google.com>
Reviewed-by: Shivaji Kant <shivajikant@google.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
---
 fs/nfs/direct.c | 37 +++++++++++++++++++------------------
 1 file changed, 19 insertions(+), 18 deletions(-)

diff --git a/fs/nfs/direct.c b/fs/nfs/direct.c
index 96995736fac2..a1479fbf4f9e 100644
--- a/fs/nfs/direct.c
+++ b/fs/nfs/direct.c
@@ -168,14 +168,8 @@ int nfs_swap_rw(struct kiocb *iocb, struct iov_iter *iter)
 static void nfs_direct_release_pages(struct page **pages, unsigned int npages,
 				     bool pinned)
 {
-	unsigned int i;
-
-	if (pinned) {
+	if (pinned)
 		unpin_user_pages(pages, npages);
-	} else {
-		for (i = 0; i < npages; i++)
-			put_page(pages[i]);
-	}
 }
 
 void nfs_init_cinfo_from_dreq(struct nfs_commit_info *cinfo,
@@ -354,16 +348,17 @@ static ssize_t nfs_direct_read_schedule_iovec(struct nfs_direct_req *dreq,
 	inode_dio_begin(inode);
 
 	while (iov_iter_count(iter)) {
-		struct page **pagevec;
+		struct page **pagevec = NULL;
 		size_t bytes;
 		size_t pgbase;
 		unsigned npages, i;
+		bool pinned = iov_iter_extract_will_pin(iter);
 
-		result = iov_iter_get_pages_alloc2(iter, &pagevec,
-						  rsize, &pgbase);
+		result = iov_iter_extract_pages(iter, &pagevec,
+						rsize, ~0U, 0, &pgbase);
 		if (result < 0)
 			break;
-	
+
 		bytes = result;
 		npages = (result + pgbase + PAGE_SIZE - 1) / PAGE_SIZE;
 		for (i = 0; i < npages; i++) {
@@ -371,7 +366,7 @@ static ssize_t nfs_direct_read_schedule_iovec(struct nfs_direct_req *dreq,
 			unsigned int req_len = min_t(size_t, bytes, PAGE_SIZE - pgbase);
 			/* XXX do we need to do the eof zeroing found in async_filler? */
 			req = nfs_page_create_from_page(dreq->ctx, pagevec[i],
-							false, pgbase, pos,
+							pinned, pgbase, pos,
 							req_len);
 			if (IS_ERR(req)) {
 				result = PTR_ERR(req);
@@ -380,6 +375,7 @@ static ssize_t nfs_direct_read_schedule_iovec(struct nfs_direct_req *dreq,
 			if (!nfs_pageio_add_request(&desc, req)) {
 				result = desc.pg_error;
 				nfs_release_request(req);
+				i++;
 				break;
 			}
 			pgbase = 0;
@@ -387,7 +383,8 @@ static ssize_t nfs_direct_read_schedule_iovec(struct nfs_direct_req *dreq,
 			requested_bytes += req_len;
 			pos += req_len;
 		}
-		nfs_direct_release_pages(pagevec, npages, false);
+		if (i < npages)
+			nfs_direct_release_pages(pagevec + i, npages - i, pinned);
 		kvfree(pagevec);
 		if (result < 0)
 			break;
@@ -891,13 +888,14 @@ static ssize_t nfs_direct_write_schedule_iovec(struct nfs_direct_req *dreq,
 
 	NFS_I(inode)->write_io += iov_iter_count(iter);
 	while (iov_iter_count(iter)) {
-		struct page **pagevec;
+		struct page **pagevec = NULL;
 		size_t bytes;
 		size_t pgbase;
 		unsigned npages, i;
+		bool pinned = iov_iter_extract_will_pin(iter);
 
-		result = iov_iter_get_pages_alloc2(iter, &pagevec,
-						  wsize, &pgbase);
+		result = iov_iter_extract_pages(iter, &pagevec,
+						wsize, ~0U, 0, &pgbase);
 		if (result < 0)
 			break;
 
@@ -908,7 +906,7 @@ static ssize_t nfs_direct_write_schedule_iovec(struct nfs_direct_req *dreq,
 			unsigned int req_len = min_t(size_t, bytes, PAGE_SIZE - pgbase);
 
 			req = nfs_page_create_from_page(dreq->ctx, pagevec[i],
-							false, pgbase, pos,
+							pinned, pgbase, pos,
 							req_len);
 			if (IS_ERR(req)) {
 				result = PTR_ERR(req);
@@ -918,6 +916,7 @@ static ssize_t nfs_direct_write_schedule_iovec(struct nfs_direct_req *dreq,
 			if (desc.pg_error < 0) {
 				nfs_free_request(req);
 				result = desc.pg_error;
+				i++;
 				break;
 			}
 
@@ -939,6 +938,7 @@ static ssize_t nfs_direct_write_schedule_iovec(struct nfs_direct_req *dreq,
 			if (desc.pg_error < 0 && desc.pg_error != -EAGAIN) {
 				result = desc.pg_error;
 				nfs_unlock_and_release_request(req);
+				i++;
 				break;
 			}
 
@@ -952,7 +952,8 @@ static ssize_t nfs_direct_write_schedule_iovec(struct nfs_direct_req *dreq,
 			desc.pg_error = 0;
 			defer = true;
 		}
-		nfs_direct_release_pages(pagevec, npages, false);
+		if (i < npages)
+			nfs_direct_release_pages(pagevec + i, npages - i, pinned);
 		kvfree(pagevec);
 		if (result < 0)
 			break;
-- 
2.55.0.691.gc56d675ccc-goog