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, 2 insertions, 0 deletions

diff --git a/include/linux/nfs_xdr.h b/include/linux/nfs_xdr.h
index 7c7320fa51aa..2d3fb6416d91 100644
--- a/include/linux/nfs_xdr.h
+++ b/include/linux/nfs_xdr.h
@@ -729,6 +729,7 @@ struct nfs_read_data {
         struct list_head        pages;  /* Coalesced read requests */
         struct nfs_page         *req;   /* multi ops per nfs_page */
         struct page             **pagevec;
+        unsigned int            npages; /* active pages in pagevec */
         struct nfs_readargs args;
         struct nfs_readres  res;
 #ifdef CONFIG_NFS_V4
@@ -747,6 +748,7 @@ struct nfs_write_data {
         struct list_head        pages;          /* Coalesced requests we wish to flush */
         struct nfs_page         *req;           /* multi ops per nfs_page */
         struct page             **pagevec;
+        unsigned int            npages;         /* active pages in pagevec */
         struct nfs_writeargs    args;           /* argument struct */
         struct nfs_writeres     res;            /* result struct */
 #ifdef CONFIG_NFS_V4