[RFC PATCH v1 09/13] NFS: Convert nfs_readpage() and readpages() to new fscache API

[Dave Wysochanski <dwysocha@redhat.com>]

This patch converts the NFS read paths to the new fscache API,
minimizing changes to the existing code.

The new fscache IO path API uses a different mechanism to read
through the cache.  There are two main read_helper calls:
- readpage: fscache_read_helper_locked_page()
  - replaces old API fscache_read_or_alloc_page()
- readpages: fscache_read_helper_page_list()
  - replaces old API fscache_read_or_alloc_pages()

Once submitted to the read_helper, if pages are inside the cache
fscache will call the done() function of fscache_io_request_ops().
If the pages are not inside the cache, fscache will call issue_op()
so NFS can go through its normal read code paths, such as
nfs_pageio_init_read(), nfs_pageio_add_page_read() and
nfs_pageio_complete_read().

In the read completion code path, from nfs_read_completion() we
must call into fscache via a cache.io_done() function.  In order
to call back into fscache via this function, we must save the
nfs_fscache_req * as a field in the nfs_pgio_header, similar to
nfs_direct_req.  Note also that when fscache is enabled, the
read_helper will lock and unlock the pages so in the completion
path we skip the unlock_page() with fscache.

Signed-off-by: Dave Wysochanski <dwysocha@redhat.com>
---
 fs/nfs/fscache.c         | 225 ++++++++++++++++++++++++-----------------------
 fs/nfs/fscache.h         |  25 +++---
 fs/nfs/pagelist.c        |   1 +
 fs/nfs/read.c            |  14 +--
 include/linux/nfs_page.h |   1 +
 include/linux/nfs_xdr.h  |   1 +
 6 files changed, 139 insertions(+), 128 deletions(-)

diff --git a/fs/nfs/fscache.c b/fs/nfs/fscache.c
index 7f380d6ec616..f8cf3ffe15c5 100644
--- a/fs/nfs/fscache.c
+++ b/fs/nfs/fscache.c
@@ -336,73 +336,96 @@ void nfs_fscache_open_file(struct inode *inode, struct file *filp)
 }
 EXPORT_SYMBOL_GPL(nfs_fscache_open_file);
 
-/*
- * Release the caching state associated with a page, if the page isn't busy
- * interacting with the cache.
- * - Returns true (can release page) or false (page busy).
- */
-int nfs_fscache_release_page(struct page *page, gfp_t gfp)
+/* HACK - remove / duplicate */
+struct nfs_readdesc {
+	struct nfs_pageio_descriptor *pgio;
+	struct nfs_open_context *ctx;
+};
+
+struct nfs_fscache_req {
+	struct fscache_io_request	cache;
+	struct nfs_readdesc             desc;
+	struct nfs_pageio_descriptor    pgio; /* HACK remove */
+	refcount_t			usage;
+};
+
+static void nfs_done_io_request(struct fscache_io_request *fsreq)
 {
-	if (PageFsCache(page)) {
-		struct fscache_cookie *cookie = nfs_i_fscache(page->mapping->host);
-
-		BUG_ON(!cookie);
-		dfprintk(FSCACHE, "NFS: fscache releasepage (0x%p/0x%p/0x%p)\n",
-			 cookie, page, NFS_I(page->mapping->host));
+	struct nfs_fscache_req *req = container_of(fsreq, struct nfs_fscache_req, cache);
+	struct inode *inode = d_inode(req->desc.ctx->dentry);
 
-		if (!fscache_maybe_release_page(cookie, page, gfp))
-			return 0;
-
-		nfs_inc_fscache_stats(page->mapping->host,
-				      NFSIOS_FSCACHE_PAGES_UNCACHED);
-	}
-
-	return 1;
+	nfs_add_fscache_stats(inode, NFSIOS_FSCACHE_PAGES_READ_OK,
+			      fsreq->transferred >> PAGE_SHIFT);
 }
 
-/*
- * Release the caching state associated with a page if undergoing complete page
- * invalidation.
- */
-void __nfs_fscache_invalidate_page(struct page *page, struct inode *inode)
+static void nfs_get_io_request(struct fscache_io_request *fsreq)
 {
-	struct fscache_cookie *cookie = nfs_i_fscache(inode);
+	struct nfs_fscache_req *req = container_of(fsreq, struct nfs_fscache_req, cache);
 
-	BUG_ON(!cookie);
+	refcount_inc(&req->usage);
+}
 
-	dfprintk(FSCACHE, "NFS: fscache invalidatepage (0x%p/0x%p/0x%p)\n",
-		 cookie, page, NFS_I(inode));
+static void nfs_put_io_request(struct fscache_io_request *fsreq)
+{
+	struct nfs_fscache_req *req = container_of(fsreq, struct nfs_fscache_req, cache);
 
-	fscache_wait_on_page_write(cookie, page);
+	if (refcount_dec_and_test(&req->usage)) {
+		put_nfs_open_context(req->desc.ctx);
+		fscache_free_io_request(fsreq);
+		kfree(req);
+	}
+}
 
-	BUG_ON(!PageLocked(page));
-	fscache_uncache_page(cookie, page);
-	nfs_inc_fscache_stats(page->mapping->host,
-			      NFSIOS_FSCACHE_PAGES_UNCACHED);
+static void nfs_issue_op(struct fscache_io_request *fsreq)
+{
+	struct nfs_fscache_req *req = container_of(fsreq, struct nfs_fscache_req, cache);
+	struct inode *inode = req->cache.mapping->host;
+	struct page *page;
+	pgoff_t index = req->cache.pos >> PAGE_SHIFT;
+	pgoff_t last = index + req->cache.nr_pages - 1;
+
+	nfs_add_fscache_stats(inode, NFSIOS_FSCACHE_PAGES_READ_FAIL,
+			      req->cache.nr_pages);
+	nfs_get_io_request(fsreq);
+	nfs_pageio_init_read(&req->pgio, inode, false,
+			     &nfs_async_read_completion_ops);
+
+	for (; index <= last; index++) {
+		page = find_get_page(req->cache.mapping, index);
+		BUG_ON(!page);
+		req->cache.error = nfs_pageio_add_page_read(&req->desc, page);
+		if (req->cache.error < 0)
+			break;
+	}
+	nfs_pageio_complete_read(&req->pgio, inode);
 }
 
-/*
- * Handle completion of a page being read from the cache.
- * - Called in process (keventd) context.
- */
-static void nfs_readpage_from_fscache_complete(struct page *page,
-					       void *context,
-					       int error)
+static struct fscache_io_request_ops nfs_fscache_req_ops = {
+	.issue_op	= nfs_issue_op,
+	.done		= nfs_done_io_request,
+	.get		= nfs_get_io_request,
+	.put		= nfs_put_io_request,
+};
+
+struct nfs_fscache_req *nfs_alloc_io_request(struct nfs_open_context *ctx,
+					    struct address_space *mapping)
 {
-	dfprintk(FSCACHE,
-		 "NFS: readpage_from_fscache_complete (0x%p/0x%p/%d)\n",
-		 page, context, error);
-
-	/* if the read completes with an error, we just unlock the page and let
-	 * the VM reissue the readpage */
-	if (!error) {
-		SetPageUptodate(page);
-		unlock_page(page);
-	} else {
-		error = nfs_readpage_async(context, page->mapping->host, page);
-		if (error)
-			unlock_page(page);
+	struct nfs_fscache_req *req;
+	struct inode *inode = mapping->host;
+
+	req = kzalloc(sizeof(*req), GFP_KERNEL);
+	if (req) {
+		refcount_set(&req->usage, 1);
+		req->cache.mapping = mapping;
+		req->desc.pgio = &req->pgio; /* HACK - remove */
+		req->desc.ctx = get_nfs_open_context(ctx);
+
+		fscache_init_io_request(&req->cache, nfs_i_fscache(inode),
+					&nfs_fscache_req_ops);
+		req->desc.pgio->pg_fsc_req = req;
 	}
+
+	return req;
 }
 
 /*
@@ -411,36 +434,38 @@ static void nfs_readpage_from_fscache_complete(struct page *page,
 int __nfs_readpage_from_fscache(struct nfs_open_context *ctx,
 				struct inode *inode, struct page *page)
 {
+	struct nfs_fscache_req *req;
 	int ret;
 
 	dfprintk(FSCACHE,
 		 "NFS: readpage_from_fscache(fsc:%p/p:%p(i:%lx f:%lx)/0x%p)\n",
 		 nfs_i_fscache(inode), page, page->index, page->flags, inode);
 
-	ret = fscache_read_or_alloc_page(nfs_i_fscache(inode),
-					 page,
-					 nfs_readpage_from_fscache_complete,
-					 ctx,
-					 GFP_KERNEL);
+	req = nfs_alloc_io_request(ctx, page_file_mapping(page));
+	if (IS_ERR(req))
+		return PTR_ERR(req);
+
+	ret = fscache_read_helper_locked_page(&req->cache, page, ULONG_MAX);
+
+	nfs_put_io_request(&req->cache);
 
 	switch (ret) {
-	case 0: /* read BIO submitted (page in fscache) */
-		dfprintk(FSCACHE,
-			 "NFS:    readpage_from_fscache: BIO submitted\n");
+	case 0: /* read submitted */
+		dfprintk(FSCACHE, "NFS:    readpage_from_fscache: submitted\n");
 		nfs_inc_fscache_stats(inode, NFSIOS_FSCACHE_PAGES_READ_OK);
 		return ret;
 
 	case -ENOBUFS: /* inode not in cache */
 	case -ENODATA: /* page not in cache */
 		nfs_inc_fscache_stats(inode, NFSIOS_FSCACHE_PAGES_READ_FAIL);
-		dfprintk(FSCACHE,
-			 "NFS:    readpage_from_fscache %d\n", ret);
+		dfprintk(FSCACHE, "NFS:    readpage_from_fscache %d\n", ret);
 		return 1;
 
 	default:
 		dfprintk(FSCACHE, "NFS:    readpage_from_fscache %d\n", ret);
 		nfs_inc_fscache_stats(inode, NFSIOS_FSCACHE_PAGES_READ_FAIL);
 	}
+
 	return ret;
 }
 
@@ -450,75 +475,57 @@ int __nfs_readpage_from_fscache(struct nfs_open_context *ctx,
 int __nfs_readpages_from_fscache(struct nfs_open_context *ctx,
 				 struct inode *inode,
 				 struct address_space *mapping,
-				 struct list_head *pages,
-				 unsigned *nr_pages)
+				 struct list_head *pages)
 {
-	unsigned npages = *nr_pages;
+	struct nfs_fscache_req *req;
 	int ret;
 
-	dfprintk(FSCACHE, "NFS: nfs_getpages_from_fscache (0x%p/%u/0x%p)\n",
-		 nfs_i_fscache(inode), npages, inode);
-
-	ret = fscache_read_or_alloc_pages(nfs_i_fscache(inode),
-					  mapping, pages, nr_pages,
-					  nfs_readpage_from_fscache_complete,
-					  ctx,
-					  mapping_gfp_mask(mapping));
-	if (*nr_pages < npages)
-		nfs_add_fscache_stats(inode, NFSIOS_FSCACHE_PAGES_READ_OK,
-				      npages);
-	if (*nr_pages > 0)
-		nfs_add_fscache_stats(inode, NFSIOS_FSCACHE_PAGES_READ_FAIL,
-				      *nr_pages);
+	dfprintk(FSCACHE, "NFS: nfs_readpages_from_fscache (0x%p/0x%p)\n",
+		 nfs_i_fscache(inode), inode);
+
+	while (!list_empty(pages)) {
+		req = nfs_alloc_io_request(ctx, mapping);
+		if (IS_ERR(req))
+			return PTR_ERR(req);
+
+		ret = fscache_read_helper_page_list(&req->cache, pages,
+						    ULONG_MAX);
+		nfs_put_io_request(&req->cache);
+		if (ret < 0)
+			break;
+	}
 
 	switch (ret) {
 	case 0: /* read submitted to the cache for all pages */
-		BUG_ON(!list_empty(pages));
-		BUG_ON(*nr_pages != 0);
 		dfprintk(FSCACHE,
-			 "NFS: nfs_getpages_from_fscache: submitted\n");
+			 "NFS: nfs_readpages_from_fscache: submitted\n");
 
 		return ret;
 
 	case -ENOBUFS: /* some pages aren't cached and can't be */
 	case -ENODATA: /* some pages aren't cached */
 		dfprintk(FSCACHE,
-			 "NFS: nfs_getpages_from_fscache: no page: %d\n", ret);
+			 "NFS: nfs_readpages_from_fscache: no page: %d\n", ret);
 		return 1;
 
 	default:
 		dfprintk(FSCACHE,
-			 "NFS: nfs_getpages_from_fscache: ret  %d\n", ret);
+			 "NFS: nfs_readpages_from_fscache: ret  %d\n", ret);
 	}
-
 	return ret;
 }
 
 /*
- * Store a newly fetched page in fscache
- * - PG_fscache must be set on the page
+ * Store a newly fetched data in fscache
  */
-void __nfs_readpage_to_fscache(struct inode *inode, struct page *page, int sync)
+void __nfs_read_completion_to_fscache(struct nfs_pgio_header *hdr, unsigned long bytes)
 {
-	int ret;
+	struct nfs_fscache_req *fsc_req = hdr->fsc_req;
 
-	dfprintk(FSCACHE,
-		 "NFS: readpage_to_fscache(fsc:%p/p:%p(i:%lx f:%lx)/%d)\n",
-		 nfs_i_fscache(inode), page, page->index, page->flags, sync);
-
-	ret = fscache_write_page(nfs_i_fscache(inode), page,
-				 inode->i_size, GFP_KERNEL);
-	dfprintk(FSCACHE,
-		 "NFS:     readpage_to_fscache: p:%p(i:%lu f:%lx) ret %d\n",
-		 page, page->index, page->flags, ret);
-
-	if (ret != 0) {
-		fscache_uncache_page(nfs_i_fscache(inode), page);
-		nfs_inc_fscache_stats(inode,
-				      NFSIOS_FSCACHE_PAGES_WRITTEN_FAIL);
-		nfs_inc_fscache_stats(inode, NFSIOS_FSCACHE_PAGES_UNCACHED);
-	} else {
-		nfs_inc_fscache_stats(inode,
-				      NFSIOS_FSCACHE_PAGES_WRITTEN_OK);
+	if (fsc_req && fsc_req->cache.io_done) {
+		fsc_req->cache.transferred = min((long long)bytes, fsc_req->cache.len);
+		set_bit(FSCACHE_IO_DATA_FROM_SERVER, &fsc_req->cache.flags);
+		fsc_req->cache.io_done(&fsc_req->cache);
+		nfs_put_io_request(&fsc_req->cache);
 	}
 }
diff --git a/fs/nfs/fscache.h b/fs/nfs/fscache.h
index 6e6d9971244a..723dc2eed5db 100644
--- a/fs/nfs/fscache.h
+++ b/fs/nfs/fscache.h
@@ -97,8 +97,9 @@ extern int __nfs_readpage_from_fscache(struct nfs_open_context *,
 				       struct inode *, struct page *);
 extern int __nfs_readpages_from_fscache(struct nfs_open_context *,
 					struct inode *, struct address_space *,
-					struct list_head *, unsigned *);
-extern void __nfs_readpage_to_fscache(struct inode *, struct page *, int);
+					struct list_head *);
+extern void __nfs_read_completion_to_fscache(struct nfs_pgio_header *hdr,
+					     unsigned long bytes);
 
 /*
  * wait for a page to complete writing to the cache
@@ -139,25 +140,22 @@ static inline int nfs_readpage_from_fscache(struct nfs_open_context *ctx,
 static inline int nfs_readpages_from_fscache(struct nfs_open_context *ctx,
 					     struct inode *inode,
 					     struct address_space *mapping,
-					     struct list_head *pages,
-					     unsigned *nr_pages)
+					     struct list_head *pages)
 {
 	if (NFS_I(inode)->fscache)
-		return __nfs_readpages_from_fscache(ctx, inode, mapping, pages,
-						    nr_pages);
+		return __nfs_readpages_from_fscache(ctx, inode, mapping, pages);
 	return -ENOBUFS;
 }
 
 /*
- * Store a page newly fetched from the server in an inode data storage object
+ * Store pages newly fetched from the server in an inode data storage object
  * in the cache.
  */
-static inline void nfs_readpage_to_fscache(struct inode *inode,
-					   struct page *page,
-					   int sync)
+static inline void nfs_read_completion_to_fscache(struct nfs_pgio_header *hdr,
+						  unsigned long bytes)
 {
-	if (PageFsCache(page))
-		__nfs_readpage_to_fscache(inode, page, sync);
+	if (NFS_I(hdr->inode)->fscache)
+		__nfs_read_completion_to_fscache(hdr, bytes);
 }
 
 /*
@@ -218,8 +216,7 @@ static inline int nfs_readpage_from_fscache(struct nfs_open_context *ctx,
 static inline int nfs_readpages_from_fscache(struct nfs_open_context *ctx,
 					     struct inode *inode,
 					     struct address_space *mapping,
-					     struct list_head *pages,
-					     unsigned *nr_pages)
+					     struct list_head *pages)
 {
 	return -ENOBUFS;
 }
diff --git a/fs/nfs/pagelist.c b/fs/nfs/pagelist.c
index 6ea4cac41e46..c8073b3667d9 100644
--- a/fs/nfs/pagelist.c
+++ b/fs/nfs/pagelist.c
@@ -52,6 +52,7 @@ void nfs_pgheader_init(struct nfs_pageio_descriptor *desc,
 	hdr->good_bytes = mirror->pg_count;
 	hdr->io_completion = desc->pg_io_completion;
 	hdr->dreq = desc->pg_dreq;
+	hdr->fsc_req = desc->pg_fsc_req;
 	hdr->release = release;
 	hdr->completion_ops = desc->pg_completion_ops;
 	if (hdr->completion_ops->init_hdr)
diff --git a/fs/nfs/read.c b/fs/nfs/read.c
index 2f2c32346212..dbf60162f2ce 100644
--- a/fs/nfs/read.c
+++ b/fs/nfs/read.c
@@ -124,10 +124,13 @@ static void nfs_readpage_release(struct nfs_page *req, int error)
 		struct address_space *mapping = page_file_mapping(page);
 
 		if (PageUptodate(page))
-			nfs_readpage_to_fscache(inode, page, 0);
+			; /* FIXME: review fscache page error handling */
 		else if (!PageError(page) && !PagePrivate(page))
 			generic_error_remove_page(mapping, page);
-		unlock_page(page);
+		if (nfs_i_fscache(inode))
+			put_page(page); /* See nfs_issue_op() */
+		else
+			unlock_page(page);
 	}
 	nfs_release_request(req);
 }
@@ -186,6 +189,8 @@ static void nfs_read_completion(struct nfs_pgio_header *hdr)
 		nfs_list_remove_request(req);
 		nfs_readpage_release(req, error);
 	}
+	/* FIXME: Review error handling before writing to fscache */
+	nfs_read_completion_to_fscache(hdr, bytes);
 out:
 	hdr->release(hdr);
 }
@@ -374,7 +379,7 @@ int nfs_readpage(struct file *filp, struct page *page)
 	nfs_pageio_init_read(desc.pgio, inode, false,
 			     &nfs_async_read_completion_ops);
 
-	ret = nfs_pageio_add_page_read(desc.pgio, page);
+	ret = nfs_pageio_add_page_read(&desc, page);
 
 	if (!ret)
 		nfs_pageio_complete_read(desc.pgio, inode);
@@ -422,8 +427,7 @@ int nfs_readpages(struct file *filp, struct address_space *mapping,
 	/* attempt to read as many of the pages as possible from the cache
 	 * - this returns -ENOBUFS immediately if the cookie is negative
 	 */
-	ret = nfs_readpages_from_fscache(desc.ctx, inode, mapping,
-					 pages, &nr_pages);
+	ret = nfs_readpages_from_fscache(desc.ctx, inode, mapping, pages);
 	if (ret == 0)
 		goto read_complete; /* all pages were read */
 
diff --git a/include/linux/nfs_page.h b/include/linux/nfs_page.h
index c32c15216da3..cf4b1a62108e 100644
--- a/include/linux/nfs_page.h
+++ b/include/linux/nfs_page.h
@@ -97,6 +97,7 @@ struct nfs_pageio_descriptor {
 	struct pnfs_layout_segment *pg_lseg;
 	struct nfs_io_completion *pg_io_completion;
 	struct nfs_direct_req	*pg_dreq;
+	struct nfs_fscache_req  *pg_fsc_req; /* fscache req - may be NULL */
 	unsigned int		pg_bsize;	/* default bsize for mirrors */
 
 	u32			pg_mirror_count;
diff --git a/include/linux/nfs_xdr.h b/include/linux/nfs_xdr.h
index 5fd0a9ef425f..746548676a51 100644
--- a/include/linux/nfs_xdr.h
+++ b/include/linux/nfs_xdr.h
@@ -1535,6 +1535,7 @@ struct nfs_pgio_header {
 	const struct nfs_rw_ops	*rw_ops;
 	struct nfs_io_completion *io_completion;
 	struct nfs_direct_req	*dreq;
+	struct nfs_fscache_req  *fsc_req;  /* fscache req - may be NULL */
 
 	int			pnfs_error;
 	int			error;		/* merge with pnfs_error */
-- 
1.8.3.1