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

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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>
This commit is contained in:
Christoph Hellwig 2014-09-10 08:23:30 -07:00 committed by Trond Myklebust
parent 7c5d187581
commit 612aa983a0
2 changed files with 22 additions and 0 deletions
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7
fs/nfs/file.c
View File

@ -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? */

15
fs/nfs/pnfs.h
View File

@ -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)
{