pnfs: add flag to force read-modify-write in ->write_begin

Like all block based filesystems, the pNFS block layout driver can't read
or write at a byte granularity and thus has to perform read-modify-write
cycles on writes smaller than this granularity.

Add a flag so that the core NFS code always reads a whole page when
starting a smaller write, so that we can do it in the place where the VFS
expects it instead of doing in very deadlock prone way in the writeback
handler.

Note that in theory we could do less than page size reads here for disks
that have a smaller sector size which are served by a server with a smaller
pnfs block size.  But so far that doesn't seem like a worthwhile
optimization.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

diff --git a/fs/nfs/file.c b/fs/nfs/file.c
index 524dd80d189862db5a76a7bb9e8a263ce857ffeb..05ef7dcc5f216870f72d0df11874dd0025ffbca4 100644 (file)
--- a/fs/nfs/file.c
+++ b/fs/nfs/file.c
@@ -36,6 +36,7 @@
 #include "internal.h"
 #include "iostat.h"
 #include "fscache.h"
+#include "pnfs.h"
 
 #include "nfstrace.h"
 
@@ -327,6 +328,12 @@ static int nfs_want_read_modify_write(struct file *file, struct page *page,
        unsigned int offset = pos & (PAGE_CACHE_SIZE - 1);
        unsigned int end = offset + len;
 
+       if (pnfs_ld_read_whole_page(file->f_mapping->host)) {
+               if (!PageUptodate(page))
+                       return 1;
+               return 0;
+       }
+
        if ((file->f_mode & FMODE_READ) &&      /* open for read? */
            !PageUptodate(page) &&              /* Uptodate? */
            !PagePrivate(page) &&               /* i/o request already? */

diff --git a/fs/nfs/pnfs.h b/fs/nfs/pnfs.h
index 8835b5a320ccf16ea23a4f62fc83938bd971f3fa..a4c530e52149432a00f08eae69579e74b3641f0f 100644 (file)
--- a/fs/nfs/pnfs.h
+++ b/fs/nfs/pnfs.h
@@ -72,6 +72,7 @@ enum layoutdriver_policy_flags {
        /* Should the pNFS client commit and return the layout upon a setattr */
        PNFS_LAYOUTRET_ON_SETATTR       = 1 << 0,
        PNFS_LAYOUTRET_ON_ERROR         = 1 << 1,
+       PNFS_READ_WHOLE_PAGE            = 1 << 2,
 };
 
 struct nfs4_deviceid_node;
@@ -369,6 +370,14 @@ pnfs_ld_layoutret_on_setattr(struct inode *inode)
                PNFS_LAYOUTRET_ON_SETATTR;
 }
 
+static inline bool
+pnfs_ld_read_whole_page(struct inode *inode)
+{
+       if (!pnfs_enabled_sb(NFS_SERVER(inode)))
+               return false;
+       return NFS_SERVER(inode)->pnfs_curr_ld->flags & PNFS_READ_WHOLE_PAGE;
+}
+
 static inline bool
 pnfs_layoutcommit_outstanding(struct inode *inode)
 {
@@ -444,6 +453,12 @@ pnfs_ld_layoutret_on_setattr(struct inode *inode)
        return false;
 }
 
+static inline bool
+pnfs_ld_read_whole_page(struct inode *inode)
+{
+       return false;
+}
+
 static inline bool
 pnfs_roc(struct inode *ino)
 {