nfs: enable swap on NFS

Implement the new swapfile a_ops for NFS and hook up ->direct_IO.  This
will set the NFS socket to SOCK_MEMALLOC and run socket reconnect under
PF_MEMALLOC as well as reset SOCK_MEMALLOC before engaging the protocol
->connect() method.

PF_MEMALLOC should allow the allocation of struct socket and related
objects and the early (re)setting of SOCK_MEMALLOC should allow us to
receive the packets required for the TCP connection buildup.

[jlayton@redhat.com: Restore PF_MEMALLOC task flags in all cases]
[dfeng@redhat.com: Fix handling of multiple swap files]
[a.p.zijlstra@chello.nl: Original patch]
Signed-off-by: Mel Gorman <mgorman@suse.de>
Acked-by: Rik van Riel <riel@redhat.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: David S. Miller <davem@davemloft.net>
Cc: Eric B Munson <emunson@mgebm.net>
Cc: Eric Paris <eparis@redhat.com>
Cc: James Morris <jmorris@namei.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Mike Christie <michaelc@cs.wisc.edu>
Cc: Neil Brown <neilb@suse.de>
Cc: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
Cc: Trond Myklebust <Trond.Myklebust@netapp.com>
Cc: Xiaotian Feng <dfeng@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

9 files changed, 149 insertions, 34 deletions

diff --git a/fs/nfs/Kconfig b/fs/nfs/Kconfig
index 404c6a8ac394..6fd5f2cdcd1e 100644
--- a/fs/nfs/Kconfig
+++ b/fs/nfs/Kconfig
@@ -86,6 +86,14 @@ config NFS_V4
 
           If unsure, say Y.
 
+config NFS_SWAP
+        bool "Provide swap over NFS support"
+        default n
+        depends on NFS_FS
+        select SUNRPC_SWAP
+        help
+          This option enables swapon to work on files located on NFS mounts.
+
 config NFS_V4_1
         bool "NFS client support for NFSv4.1 (EXPERIMENTAL)"
         depends on NFS_V4 && EXPERIMENTAL
diff --git a/fs/nfs/direct.c b/fs/nfs/direct.c
index 42dce909ec70..bf9c8d0ec16a 100644
--- a/fs/nfs/direct.c
+++ b/fs/nfs/direct.c
@@ -115,17 +115,28 @@ static inline int put_dreq(struct nfs_direct_req *dreq)
  * @nr_segs: size of iovec array
  *
  * The presence of this routine in the address space ops vector means
- * the NFS client supports direct I/O.  However, we shunt off direct
- * read and write requests before the VFS gets them, so this method
- * should never be called.
+ * the NFS client supports direct I/O. However, for most direct IO, we
+ * shunt off direct read and write requests before the VFS gets them,
+ * so this method is only ever called for swap.
  */
 ssize_t nfs_direct_IO(int rw, struct kiocb *iocb, const struct iovec *iov, loff_t pos, unsigned long nr_segs)
 {
+#ifndef CONFIG_NFS_SWAP
         dprintk("NFS: nfs_direct_IO (%s) off/no(%Ld/%lu) EINVAL\n",
                         iocb->ki_filp->f_path.dentry->d_name.name,
                         (long long) pos, nr_segs);
 
         return -EINVAL;
+#else
+        VM_BUG_ON(iocb->ki_left != PAGE_SIZE);
+        VM_BUG_ON(iocb->ki_nbytes != PAGE_SIZE);
+
+        if (rw == READ || rw == KERNEL_READ)
+                return nfs_file_direct_read(iocb, iov, nr_segs, pos,
+                                rw == READ ? true : false);
+        return nfs_file_direct_write(iocb, iov, nr_segs, pos,
+                                rw == WRITE ? true : false);
+#endif /* CONFIG_NFS_SWAP */
 }
 
 static void nfs_direct_release_pages(struct page **pages, unsigned int npages)
@@ -303,7 +314,7 @@ static const struct nfs_pgio_completion_ops nfs_direct_read_completion_ops = {
  */
 static ssize_t nfs_direct_read_schedule_segment(struct nfs_pageio_descriptor *desc,
                                                 const struct iovec *iov,
-                                                loff_t pos)
+                                                loff_t pos, bool uio)
 {
         struct nfs_direct_req *dreq = desc->pg_dreq;
         struct nfs_open_context *ctx = dreq->ctx;
@@ -331,12 +342,20 @@ static ssize_t nfs_direct_read_schedule_segment(struct nfs_pageio_descriptor *de
                                           GFP_KERNEL);
                 if (!pagevec)
                         break;
-                down_read(&current->mm->mmap_sem);
-                result = get_user_pages(current, current->mm, user_addr,
+                if (uio) {
+                        down_read(&current->mm->mmap_sem);
+                        result = get_user_pages(current, current->mm, user_addr,
                                         npages, 1, 0, pagevec, NULL);
-                up_read(&current->mm->mmap_sem);
-                if (result < 0)
-                        break;
+                        up_read(&current->mm->mmap_sem);
+                        if (result < 0)
+                                break;
+                } else {
+                        WARN_ON(npages != 1);
+                        result = get_kernel_page(user_addr, 1, pagevec);
+                        if (WARN_ON(result != 1))
+                                break;
+                }
+
                 if ((unsigned)result < npages) {
                         bytes = result * PAGE_SIZE;
                         if (bytes <= pgbase) {
@@ -386,7 +405,7 @@ static ssize_t nfs_direct_read_schedule_segment(struct nfs_pageio_descriptor *de
 static ssize_t nfs_direct_read_schedule_iovec(struct nfs_direct_req *dreq,
                                               const struct iovec *iov,
                                               unsigned long nr_segs,
-                                              loff_t pos)
+                                              loff_t pos, bool uio)
 {
         struct nfs_pageio_descriptor desc;
         ssize_t result = -EINVAL;
@@ -400,7 +419,7 @@ static ssize_t nfs_direct_read_schedule_iovec(struct nfs_direct_req *dreq,
 
         for (seg = 0; seg < nr_segs; seg++) {
                 const struct iovec *vec = &iov[seg];
-                result = nfs_direct_read_schedule_segment(&desc, vec, pos);
+                result = nfs_direct_read_schedule_segment(&desc, vec, pos, uio);
                 if (result < 0)
                         break;
                 requested_bytes += result;
@@ -426,7 +445,7 @@ static ssize_t nfs_direct_read_schedule_iovec(struct nfs_direct_req *dreq,
 }
 
 static ssize_t nfs_direct_read(struct kiocb *iocb, const struct iovec *iov,
-                               unsigned long nr_segs, loff_t pos)
+                               unsigned long nr_segs, loff_t pos, bool uio)
 {
         ssize_t result = -ENOMEM;
         struct inode *inode = iocb->ki_filp->f_mapping->host;
@@ -444,7 +463,7 @@ static ssize_t nfs_direct_read(struct kiocb *iocb, const struct iovec *iov,
         if (!is_sync_kiocb(iocb))
                 dreq->iocb = iocb;
 
-        result = nfs_direct_read_schedule_iovec(dreq, iov, nr_segs, pos);
+        result = nfs_direct_read_schedule_iovec(dreq, iov, nr_segs, pos, uio);
         if (!result)
                 result = nfs_direct_wait(dreq);
         NFS_I(inode)->read_io += result;
@@ -610,7 +629,7 @@ static void nfs_direct_write_complete(struct nfs_direct_req *dreq, struct inode
  */
 static ssize_t nfs_direct_write_schedule_segment(struct nfs_pageio_descriptor *desc,
                                                  const struct iovec *iov,
-                                                 loff_t pos)
+                                                 loff_t pos, bool uio)
 {
         struct nfs_direct_req *dreq = desc->pg_dreq;
         struct nfs_open_context *ctx = dreq->ctx;
@@ -638,12 +657,19 @@ static ssize_t nfs_direct_write_schedule_segment(struct nfs_pageio_descriptor *d
                 if (!pagevec)
                         break;
 
-                down_read(&current->mm->mmap_sem);
-                result = get_user_pages(current, current->mm, user_addr,
-                                        npages, 0, 0, pagevec, NULL);
-                up_read(&current->mm->mmap_sem);
-                if (result < 0)
-                        break;
+                if (uio) {
+                        down_read(&current->mm->mmap_sem);
+                        result = get_user_pages(current, current->mm, user_addr,
+                                                npages, 0, 0, pagevec, NULL);
+                        up_read(&current->mm->mmap_sem);
+                        if (result < 0)
+                                break;
+                } else {
+                        WARN_ON(npages != 1);
+                        result = get_kernel_page(user_addr, 0, pagevec);
+                        if (WARN_ON(result != 1))
+                                break;
+                }
 
                 if ((unsigned)result < npages) {