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From:   Trond Myklebust <trondmy@gmail.com>
To:     linux-nfs@vger.kernel.org
Cc:     Liguang Zhang <zhangliguang@linux.alibaba.com>
Subject: [PATCH 2/3] NFS: Reduce stack usage in nfs_readdir()
Date:   Sat,  6 Jul 2019 14:52:51 -0400
Message-Id: <20190706185252.32488-2-trond.myklebust@hammerspace.com>
In-Reply-To: <20190706185252.32488-1-trond.myklebust@hammerspace.com>
References: <20190706185252.32488-1-trond.myklebust@hammerspace.com>
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Sender: linux-nfs-owner@vger.kernel.org
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64 pointers is 512bytes on a typical 64-bit system.

Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
---
 fs/nfs/dir.c | 29 +++++++++++++++++++----------
 1 file changed, 19 insertions(+), 10 deletions(-)

diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
index e44f3c9fad5b..6ccf0e6c9c84 100644
--- a/fs/nfs/dir.c
+++ b/fs/nfs/dir.c
@@ -646,12 +646,12 @@ void nfs_readdir_rapages_init(nfs_readdir_descriptor_t *desc)
 static
 int nfs_readdir_xdr_to_array(nfs_readdir_descriptor_t *desc, struct page *page, struct inode *inode)
 {
-	struct page *pages[NFS_MAX_READDIR_PAGES];
+	const unsigned int array_size = NFS_MAX_READDIR_PAGES;
+	struct page **pages;
 	struct nfs_entry entry;
 	struct file	*file = desc->file;
 	struct nfs_cache_array *array;
 	int status = -ENOMEM;
-	unsigned int array_size = ARRAY_SIZE(pages);
 
 	/*
 	 * This means we hit readdir rdpages miss, the preallocated rdpages
@@ -674,12 +674,17 @@ int nfs_readdir_xdr_to_array(nfs_readdir_descriptor_t *desc, struct page *page,
 		goto out;
 	}
 
-	array = kmap(page);
-	memset(array, 0, sizeof(struct nfs_cache_array));
+	pages = kmalloc_array(array_size, sizeof(*pages), GFP_KERNEL);
+	if (!pages)
+		goto out_release_array;
 
 	status = nfs_readdir_alloc_pages(pages, array_size);
 	if (status < 0)
 		goto out_release_array;
+
+	array = kmap(page);
+	memset(array, 0, sizeof(struct nfs_cache_array));
+
 	do {
 		unsigned int pglen;
 		status = nfs_readdir_xdr_filler(pages, desc, &entry, file, inode);
@@ -695,9 +700,10 @@ int nfs_readdir_xdr_to_array(nfs_readdir_descriptor_t *desc, struct page *page,
 		}
 	} while (!array->eof);
 
+	kunmap(page);
 	nfs_readdir_free_pages(pages, array_size);
 out_release_array:
-	kunmap(page);
+	kfree(pages);
 	nfs4_label_free(entry.label);
 out:
 	nfs_free_fattr(entry.fattr);
@@ -896,10 +902,9 @@ static int nfs_readdir(struct file *file, struct dir_context *ctx)
 {
 	struct dentry	*dentry = file_dentry(file);
 	struct inode	*inode = d_inode(dentry);
-	nfs_readdir_descriptor_t my_desc,
-			*desc = &my_desc;
 	struct nfs_open_dir_context *dir_ctx = file->private_data;
-	int res = 0;
+	nfs_readdir_descriptor_t *desc;
+	int res = -ENOMEM;
 	unsigned int max_rapages = NFS_MAX_READDIR_RAPAGES;
 
 	dfprintk(FILE, "NFS: readdir(%pD2) starting at cookie %llu\n",
@@ -912,7 +917,9 @@ static int nfs_readdir(struct file *file, struct dir_context *ctx)
 	 * to either find the entry with the appropriate number or
 	 * revalidate the cookie.
 	 */
-	memset(desc, 0, sizeof(*desc));
+	desc = kzalloc(sizeof(*desc), GFP_KERNEL);
+	if (!desc)
+		goto free_desc;
 
 	desc->file = file;
 	desc->ctx = ctx;
@@ -922,7 +929,7 @@ static int nfs_readdir(struct file *file, struct dir_context *ctx)
 
 	res = nfs_readdir_alloc_pages(desc->pvec.pages, max_rapages);
 	if (res < 0)
-		return -ENOMEM;
+		goto free_desc;
 
 	nfs_readdir_rapages_init(desc);
 
@@ -964,6 +971,8 @@ static int nfs_readdir(struct file *file, struct dir_context *ctx)
 	nfs_readdir_free_pages(desc->pvec.pages, max_rapages);
 	if (res > 0)
 		res = 0;
+free_desc:
+	kfree(desc);
 	dfprintk(FILE, "NFS: readdir(%pD2) returns %d\n", file, res);
 	return res;
 }
-- 
2.21.0