NFS: Eliminate nfs_get_user_pages()

Neil Brown observed that the kmalloc() in nfs_get_user_pages() is more
likely to fail if the I/O is large enough to require the allocation of more
than a single page to keep track of all the pinned pages in the user's
buffer.

Instead of tracking one large page array per dreq/iocb, track pages per
nfs_read/write_data, just like the cached I/O path does.  An array for
pages is already allocated for us by nfs_readdata_alloc() (and the write
and commit equivalents).

This is also required for adding support for vectored I/O to the NFS direct
I/O path.

The original reason to pin the user buffer and allocate all the NFS data
structures before trying to schedule I/O was to ensure all needed resources
are allocated on the client before starting to send requests.  This reduces
the chance that resource exhaustion on the client will cause a short read
or write.

On the other hand, for an application making very large application I/O
requests, this means that it will be nearly impossible for the application
to make forward progress on a resource-limited client.

Thus, moving the buffer pinning functionality into the I/O scheduling
loops should be good for scalability.  The next patch will do the same for
NFS data structure allocation.

Signed-off-by: Chuck Lever <cel@netapp.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

1 files changed, 111 insertions, 94 deletions

diff --git a/fs/nfs/direct.c b/fs/nfs/direct.c
index 4cb3446220b..b1630d53fbb 100644
--- a/fs/nfs/direct.c
+++ b/fs/nfs/direct.c
@@ -73,8 +73,6 @@ struct nfs_direct_req {
         struct nfs_open_context *ctx;           /* file open context info */
         struct kiocb *          iocb;           /* controlling i/o request */
         struct inode *          inode;          /* target file of i/o */
-        struct page **          pages;          /* pages in our buffer */
-        unsigned int            npages;         /* count of pages */
 
         /* completion state */
         atomic_t                io_count;       /* i/os we're waiting for */
@@ -104,6 +102,20 @@ static inline int put_dreq(struct nfs_direct_req *dreq)
         return atomic_dec_and_test(&dreq->io_count);
 }
 
+/*
+ * "size" is never larger than rsize or wsize.
+ */
+static inline int nfs_direct_count_pages(unsigned long user_addr, size_t size)
+{
+        int page_count;
+
+        page_count = (user_addr + size + PAGE_SIZE - 1) >> PAGE_SHIFT;
+        page_count -= user_addr >> PAGE_SHIFT;
+        BUG_ON(page_count < 0);
+
+        return page_count;
+}
+
 /**
  * nfs_direct_IO - NFS address space operation for direct I/O
  * @rw: direction (read or write)
@@ -143,40 +155,6 @@ static void nfs_direct_release_pages(struct page **pages, int npages)
                 page_cache_release(pages[i]);
 }
 
-static inline int nfs_get_user_pages(int rw, unsigned long user_addr, size_t size, struct page ***pages)
-{
-        int result = -ENOMEM;
-        unsigned long page_count;
-        size_t array_size;
-
-        page_count = (user_addr + size + PAGE_SIZE - 1) >> PAGE_SHIFT;
-        page_count -= user_addr >> PAGE_SHIFT;
-
-        array_size = (page_count * sizeof(struct page *));
-        *pages = kmalloc(array_size, GFP_KERNEL);
-        if (*pages) {
-                down_read(&current->mm->mmap_sem);
-                result = get_user_pages(current, current->mm, user_addr,
-                                        page_count, (rw == READ), 0,
-                                        *pages, NULL);
-                up_read(&current->mm->mmap_sem);
-                if (result != page_count) {
-                        /*
-                         * If we got fewer pages than expected from
-                         * get_user_pages(), the user buffer runs off the
-                         * end of a mapping; return EFAULT.
-                         */
-                        if (result >= 0) {
-                                nfs_direct_release_pages(*pages, result);
-                                result = -EFAULT;
-                        } else
-                                kfree(*pages);
-                        *pages = NULL;
-                }
-        }
-        return result;
-}
-
 static inline struct nfs_direct_req *nfs_direct_req_alloc(void)
 {
         struct nfs_direct_req *dreq;
@@ -233,13 +211,8 @@ out:
 }
 
 /*
- * We must hold a reference to all the pages in this direct read request
- * until the RPCs complete.  This could be long *after* we are woken up in
- * nfs_direct_wait (for instance, if someone hits ^C on a slow server).
- *
- * In addition, synchronous I/O uses a stack-allocated iocb.  Thus we
- * can't trust the iocb is still valid here if this is a synchronous
- * request.  If the waiter is woken prematurely, the iocb is long gone.
+ * Synchronous I/O uses a stack-allocated iocb.  Thus we can't trust
+ * the iocb is still valid here if this is a synchronous request.
  */
 static void nfs_direct_complete(struct nfs_direct_req *dreq)
 {
@@ -297,6 +270,11 @@ static struct nfs_direct_req *nfs_direct_read_alloc(size_t nbytes, size_t rsize)
         return dreq;
 }
 
+/*
+ * We must hold a reference to all the pages in this direct read request
+ * until the RPCs complete.  This could be long *after* we are woken up in
+ * nfs_direct_wait (for instance, if someone hits ^C on a slow server).
+ */
 static void nfs_direct_read_result(struct rpc_task *task, void *calldata)
 {
         struct nfs_read_data *data = calldata;
@@ -305,6 +283,9 @@ static void nfs_direct_read_result(struct rpc_task *task, void *calldata)
         if (nfs_readpage_result(task, data) != 0)
                 return;
 
+        nfs_direct_dirty_pages(data->pagevec, data->npages);
+        nfs_direct_release_pages(data->pagevec, data->npages);
+
         spin_lock(&dreq->lock);
 
         if (likely(task->tk_status >= 0))
@@ -314,11 +295,8 @@ static void nfs_direct_read_result(struct rpc_task *task, void *calldata)
 
         spin_unlock(&dreq->lock);
 
-        if (put_dreq(dreq)) {
-                nfs_direct_dirty_pages(dreq->pages, dreq->npages);
-                nfs_direct_release_pages(dreq->pages, dreq->npages);
+        if (put_dreq(dreq))
                 nfs_direct_complete(dreq);
-        }
 }
 
 static const struct rpc_call_ops nfs_read_direct_ops = {
@@ -328,21 +306,23 @@ static const struct rpc_call_ops nfs_read_direct_ops = {
 
 /*
  * For each nfs_read_data struct that was allocated on the list, dispatch
- * an NFS READ operation
+ * an NFS READ operation.  If get_user_pages() fails, we stop sending reads.
+ * Read length accounting is handled by nfs_direct_read_result().
+ * Otherwise, if no requests have been sent, just return an error.
  */
-static void nfs_direct_read_schedule(struct nfs_direct_req *dreq, unsigned long user_addr, size_t count, loff_t pos)
+static ssize_t nfs_direct_read_schedule(struct nfs_direct_req *dreq, unsigned long user_addr, size_t count, loff_t pos)
 {
         struct nfs_open_context *ctx = dreq->ctx;
         struct inode *inode = ctx->dentry->d_inode;
         struct list_head *list = &dreq->list;
-        struct page **pages = dreq->pages;
         size_t rsize = NFS_SERVER(inode)->rsize;
-        unsigned int curpage, pgbase;
+        unsigned int pgbase;
+        int result;
+        ssize_t started = 0;
+        struct nfs_read_data *data;
 
-        curpage = 0;
         pgbase = user_addr & ~PAGE_MASK;
         do {
-                struct nfs_read_data *data;
                 size_t bytes;
 
                 bytes = rsize;
@@ -353,13 +333,21 @@ static void nfs_direct_read_schedule(struct nfs_direct_req *dreq, unsigned long
                 data = list_entry(list->next, struct nfs_read_data, pages);
                 list_del_init(&data->pages);
 
+                data->npages = nfs_direct_count_pages(user_addr, bytes);
+                down_read(&current->mm->mmap_sem);
+                result = get_user_pages(current, current->mm, user_addr,
+                                        data->npages, 1, 0, data->pagevec, NULL);
+                up_read(&current->mm->mmap_sem);
+                if (unlikely(result < data->npages))
+                        goto out_err;
+
                 data->inode = inode;
                 data->cred = ctx->cred;
                 data->args.fh = NFS_FH(inode);
                 data->args.context = ctx;
                 data->args.offset = pos;
                 data->args.pgbase = pgbase;
-                data->args.pages = &pages[curpage];
+                data->args.pages = data->pagevec;
                 data->args.count = bytes;
                 data->res.fattr = &data->fattr;
                 data->res.eof = 0;
@@ -382,17 +370,36 @@ static void nfs_direct_read_schedule(struct nfs_direct_req *dreq, unsigned long
                                 bytes,
                                 (unsigned long long)data->args.offset);
 
+                started += bytes;
+                user_addr += bytes;
                 pos += bytes;
                 pgbase += bytes;
-                curpage += pgbase >> PAGE_SHIFT;
                 pgbase &= ~PAGE_MASK;
 
                 count -= bytes;
         } while (count != 0);
         BUG_ON(!list_empty(list));
+        return 0;
+
+out_err:
+        if (result > 0)
+                nfs_direct_release_pages(data->pagevec, result);
+
+        list_add(&data->pages, list);
+        while (!list_empty(list)) {
+                data = list_entry(list->next, struct nfs_read_data, pages);
+                list_del(&data->pages);
+                nfs_readdata_free(data);
+                if (put_dreq(dreq))
+                        nfs_direct_complete(dreq);
+        }
+
+        if (started)
+                return 0;
+        return result < 0 ? (ssize_t) result : -EFAULT;
 }
 
-static ssize_t nfs_direct_read(struct kiocb *iocb, unsigned long user_addr, size_t count, loff_t pos, struct page **pages, unsigned int nr_pages)
+static ssize_t nfs_direct_read(struct kiocb *iocb, unsigned long user_addr, size_t count, loff_t pos)
 {
         ssize_t result;
         sigset_t oldset;
@@ -404,8 +411,6 @@ static ssize_t nfs_direct_read(struct kiocb *iocb, unsigned long user_addr, size
         if (!dreq)
                 return -ENOMEM;
 
-        dreq->pages = pages;
-        dreq->npages = nr_pages;
         dreq->inode = inode;
         dreq->ctx = get_nfs_open_context((struct nfs_open_context *)iocb->ki_filp->private_data);
         if (!is_sync_kiocb(iocb))
@@ -413,8 +418,9 @@ static ssize_t nfs_direct_read(struct kiocb *iocb, unsigned long user_addr, size
 
         nfs_add_stats(inode, NFSIOS_DIRECTREADBYTES, count);
         rpc_clnt_sigmask(clnt, &oldset);
-        nfs_direct_read_schedule(dreq, user_addr, count, pos);
-        result = nfs_direct_wait(dreq);
+        result = nfs_direct_read_schedule(dreq, user_addr, count, pos);
+        if (!result)
+                result = nfs_direct_wait(dreq);
         rpc_clnt_sigunmask(clnt, &oldset);
 
         return result;
@@ -426,9 +432,9 @@ static void nfs_direct_free_writedata(struct nfs_direct_req *dreq)
         while (!list_empty(&dreq->list)) {
                 struct nfs_write_data *data = list_entry(dreq->list.next, struct nfs_write_data, pages);
                 list_del(&data->pages);
+                nfs_direct_release_pages(data->pagevec, data->npages);
                 nfs_writedata_release(data);
         }
-        nfs_direct_release_pages(dreq->pages, dreq->npages);
 }
 
 #if defined(CONFIG_NFS_V3) || defined(CONFIG_NFS_V4)
@@ -672,21 +678,23 @@ static const struct rpc_call_ops nfs_write_direct_ops = {
 
 /*
  * For each nfs_write_data struct that was allocated on the list, dispatch
- * an NFS WRITE operation
+ * an NFS WRITE operation.  If get_user_pages() fails, we stop sending writes.
+ * Write length accounting is handled by nfs_direct_write_result().
+ * Otherwise, if no requests have been sent, just return an error.
  */
-static void nfs_direct_write_schedule(struct nfs_direct_req *dreq, unsigned long user_addr, size_t count, loff_t pos, int sync)
+static ssize_t nfs_direct_write_schedule(struct nfs_direct_req *dreq, unsigned long user_addr, size_t count, loff_t pos, int sync)
 {
         struct nfs_open_context *ctx = dreq->ctx;
         struct inode *inode = ctx->dentry->d_inode;
         struct list_head *list = &dreq->list;
-        struct page **pages = dreq->pages;
         size_t wsize = NFS_SERVER(inode)->wsize;
-        unsigned int curpage, pgbase;
+        unsigned int pgbase;
+        int result;
+        ssize_t started = 0;
+        struct nfs_write_data *data;
 
-        curpage = 0;
         pgbase = user_addr & ~PAGE_MASK;
         do {
-                struct nfs_write_data *data;
                 size_t bytes;
 
                 bytes = wsize;
@@ -695,6 +703,15 @@ static void nfs_direct_write_schedule(struct nfs_direct_req *dreq, unsigned long
 
                 BUG_ON(list_empty(list));
                 data = list_entry(list->next, struct nfs_write_data, pages);
+
+                data->npages = nfs_direct_count_pages(user_addr, bytes);
+                down_read(&current->mm->mmap_sem);
+                result = get_user_pages(current, current->mm, user_addr,
+                                        data->npages, 0, 0, data->pagevec, NULL);
+                up_read(&current->mm->mmap_sem);
+                if (unlikely(result < data->npages))
+                        goto out_err;
+
                 list_move_tail(&data->pages, &dreq->rewrite_list);
 
                 data->inode = inode;
@@ -703,7 +720,7 @@ static void nfs_direct_write_schedule(struct nfs_direct_req *dreq, unsigned long
                 data->args.context = ctx;
                 data->args.offset = pos;
                 data->args.pgbase = pgbase;
-                data->args.pages = &pages[curpage];
+                data->args.pages = data->pagevec;
                 data->args.count = bytes;
                 data->res.fattr = &data->fattr;
                 data->res.count = bytes;
@@ -727,17 +744,36 @@ static void nfs_direct_write_schedule(struct nfs_direct_req *dreq, unsigned long
                                 bytes,
                                 (unsigned long long)data->args.offset);
 
+                started += bytes;
+                user_addr += bytes;
                 pos += bytes;
                 pgbase += bytes;
-                curpage += pgbase >> PAGE_SHIFT;
                 pgbase &= ~PAGE_MASK;
 
                 count -= bytes;
         } while (count != 0);
         BUG_ON(!list_empty(list));
+        return 0;
+
+out_err:
+        if (result > 0)
+                nfs_direct_release_pages(data->pagevec, result);
+
+        list_add(&data->pages, list);
+        while (!list_empty(list)) {
+                data = list_entry(list->next, struct nfs_write_data, pages);
+                list_del(&data->pages);
+                nfs_writedata_free(data);
+                if (put_dreq(dreq))
+                        nfs_direct_write_complete(dreq, inode);
+        }
+
+        if (started)
+                return 0;
+        return result < 0 ? (ssize_t) result : -EFAULT;
 }
 
-static ssize_t nfs_direct_write(struct kiocb *iocb, unsigned long user_addr, size_t count, loff_t pos, struct page **pages, int nr_pages)
+static ssize_t nfs_direct_write(struct kiocb *iocb, unsigned long user_addr, size_t count, loff_t pos)
 {
         ssize_t result;
         sigset_t oldset;
@@ -753,8 +789,6 @@ static ssize_t nfs_direct_write(struct kiocb *iocb, unsigned long user_addr, siz
         if (dreq->commit_data == NULL || count < wsize)
                 sync = FLUSH_STABLE;
 
-        dreq->pages = pages;
-        dreq->npages = nr_pages;
         dreq->inode = inode;
         dreq->ctx = get_nfs_open_context((struct nfs_open_context *)iocb->ki_filp->private_data);
         if (!is_sync_kiocb(iocb))
@@ -765,8 +799,9 @@ static ssize_t nfs_direct_write(struct kiocb *iocb, unsigned long user_addr, siz
         nfs_begin_data_update(inode);
 
         rpc_clnt_sigmask(clnt, &oldset);
-        nfs_direct_write_schedule(dreq, user_addr, count, pos, sync);
-        result = nfs_direct_wait(dreq);
+        result = nfs_direct_write_schedule(dreq, user_addr, count, pos, sync);
+        if (!result)
+                result = nfs_direct_wait(dreq);
         rpc_clnt_sigunmask(clnt, &oldset);
 
         return result;
@@ -796,8 +831,6 @@ static ssize_t nfs_direct_write(struct kiocb *iocb, unsigned long user_addr, siz
 ssize_t nfs_file_direct_read(struct kiocb *iocb, char __user *buf, size_t count, loff_t pos)
 {
         ssize_t retval = -EINVAL;
-        int page_count;
-        struct page **pages;
         struct file *file = iocb->ki_filp;
         struct address_space *mapping = file->f_mapping;
 
@@ -819,14 +852,7 @@ ssize_t nfs_file_direct_read(struct kiocb *iocb, char __user *buf, size_t count,
         if (retval)
                 goto out;
 
-        retval = nfs_get_user_pages(READ, (unsigned long) buf,
-                                                count, &pages);
-        if (retval < 0)
-                goto out;
-        page_count = retval;
-
-        retval = nfs_direct_read(iocb, (unsigned long) buf, count, pos,
-                                                pages, page_count);
+        retval = nfs_direct_read(iocb, (unsigned long) buf, count, pos);
         if (retval > 0)
                 iocb->ki_pos = pos + retval;
 
@@ -862,8 +888,6 @@ out:
 ssize_t nfs_file_direct_write(struct kiocb *iocb, const char __user *buf, size_t count, loff_t pos)
 {
         ssize_t retval;
-        int page_count;
-        struct page **pages;
         struct file *file = iocb->ki_filp;
         struct address_space *mapping = file->f_mapping;
 
@@ -891,14 +915,7 @@ ssize_t nfs_file_direct_write(struct kiocb *iocb, const char __user *buf, size_t
         if (retval)
                 goto out;
 
-        retval = nfs_get_user_pages(WRITE, (unsigned long) buf,
-                                                count, &pages);
-        if (retval < 0)
-                goto out;
-        page_count = retval;
-
-        retval = nfs_direct_write(iocb, (unsigned long) buf, count,
-                                        pos, pages, page_count);
+        retval = nfs_direct_write(iocb, (unsigned long) buf, count, pos);
 
         /*
          * XXX: nfs_end_data_update() already ensures this file's