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From:   trondmy@gmail.com
To:     linux-nfs@vger.kernel.org
Subject: [PATCH v3 05/17] NFS: Don't discard readdir results
Date:   Wed,  4 Nov 2020 11:16:26 -0500
Message-Id: <20201104161638.300324-6-trond.myklebust@hammerspace.com>
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From: Trond Myklebust <trond.myklebust@hammerspace.com>

If a readdir call returns more data than we can fit into one page
cache page, then allocate a new one for that data rather than
discarding the data.

Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
---
 fs/nfs/dir.c | 46 ++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 42 insertions(+), 4 deletions(-)

diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
index 842f69120a01..f7248145c333 100644
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -320,6 +320,26 @@ static void nfs_readdir_page_set_eof(struct page *page)
 	kunmap_atomic(array);
 }
 
+static void nfs_readdir_page_unlock_and_put(struct page *page)
+{
+	unlock_page(page);
+	put_page(page);
+}
+
+static struct page *nfs_readdir_page_get_next(struct address_space *mapping,
+					      pgoff_t index, u64 cookie)
+{
+	struct page *page;
+
+	page = nfs_readdir_page_get_locked(mapping, index, cookie);
+	if (page) {
+		if (nfs_readdir_page_last_cookie(page) == cookie)
+			return page;
+		nfs_readdir_page_unlock_and_put(page);
+	}
+	return NULL;
+}
+
 static inline
 int is_32bit_api(void)
 {
@@ -637,13 +657,15 @@ void nfs_prime_dcache(struct dentry *parent, struct nfs_entry *entry,
 }
 
 /* Perform conversion from xdr to cache array */
-static
-int nfs_readdir_page_filler(nfs_readdir_descriptor_t *desc, struct nfs_entry *entry,
-				struct page **xdr_pages, struct page *page, unsigned int buflen)
+static int nfs_readdir_page_filler(struct nfs_readdir_descriptor *desc,
+				   struct nfs_entry *entry,
+				   struct page **xdr_pages,
+				   struct page *fillme, unsigned int buflen)
 {
+	struct address_space *mapping = desc->file->f_mapping;
 	struct xdr_stream stream;
 	struct xdr_buf buf;
-	struct page *scratch;
+	struct page *scratch, *new, *page = fillme;
 	int status;
 
 	scratch = alloc_page(GFP_KERNEL);
@@ -666,6 +688,19 @@ int nfs_readdir_page_filler(nfs_readdir_descriptor_t *desc, struct nfs_entry *en
 					desc->dir_verifier);
 
 		status = nfs_readdir_add_to_array(entry, page);
+		if (status != -ENOSPC)
+			continue;
+
+		if (page->mapping != mapping)
+			break;
+		new = nfs_readdir_page_get_next(mapping, page->index + 1,
+						entry->prev_cookie);
+		if (!new)
+			break;
+		if (page != fillme)
+			nfs_readdir_page_unlock_and_put(page);
+		page = new;
+		status = nfs_readdir_add_to_array(entry, page);
 	} while (!status && !entry->eof);
 
 	switch (status) {
@@ -681,6 +716,9 @@ int nfs_readdir_page_filler(nfs_readdir_descriptor_t *desc, struct nfs_entry *en
 		break;
 	}
 
+	if (page != fillme)
+		nfs_readdir_page_unlock_and_put(page);
+
 	put_page(scratch);
 	return status;
 }
-- 
2.28.0