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Subject[PATCH 27/35] nfs: livelock prevention is now done in VFS
This reverts commit 72cb77f4a5 ("NFS: Throttle page dirtying while we're
flushing to disk"). The two problems it tries to address

- sync live lock
- out of order writes

are now all addressed in the VFS

- PAGECACHE_TAG_TOWRITE prevents sync live lock
- IO-less balance_dirty_pages() avoids concurrent writes

CC: Trond Myklebust <Trond.Myklebust@netapp.com>
Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
---
fs/nfs/file.c | 9 ---------
fs/nfs/write.c | 11 -----------
include/linux/nfs_fs.h | 1 -
3 files changed, 21 deletions(-)
--- linux-next.orig/fs/nfs/file.c 2010-12-13 21:45:55.000000000 +0800
+++ linux-next/fs/nfs/file.c 2010-12-13 21:46:20.000000000 +0800
@@ -392,15 +392,6 @@ static int nfs_write_begin(struct file *
IOMODE_RW);

start:
- /*
- * Prevent starvation issues if someone is doing a consistency
- * sync-to-disk
- */
- ret = wait_on_bit(&NFS_I(mapping->host)->flags, NFS_INO_FLUSHING,
- nfs_wait_bit_killable, TASK_KILLABLE);
- if (ret)
- return ret;
-
page = grab_cache_page_write_begin(mapping, index, flags);
if (!page)
return -ENOMEM;
--- linux-next.orig/fs/nfs/write.c 2010-12-13 21:45:55.000000000 +0800
+++ linux-next/fs/nfs/write.c 2010-12-13 21:46:20.000000000 +0800
@@ -337,26 +337,15 @@ static int nfs_writepages_callback(struc
int nfs_writepages(struct address_space *mapping, struct writeback_control *wbc)
{
struct inode *inode = mapping->host;
- unsigned long *bitlock = &NFS_I(inode)->flags;
struct nfs_pageio_descriptor pgio;
int err;

- /* Stop dirtying of new pages while we sync */
- err = wait_on_bit_lock(bitlock, NFS_INO_FLUSHING,
- nfs_wait_bit_killable, TASK_KILLABLE);
- if (err)
- goto out_err;
-
nfs_inc_stats(inode, NFSIOS_VFSWRITEPAGES);

nfs_pageio_init_write(&pgio, inode, wb_priority(wbc));
err = write_cache_pages(mapping, wbc, nfs_writepages_callback, &pgio);
nfs_pageio_complete(&pgio);

- clear_bit_unlock(NFS_INO_FLUSHING, bitlock);
- smp_mb__after_clear_bit();
- wake_up_bit(bitlock, NFS_INO_FLUSHING);
-
if (err < 0)
goto out_err;
err = pgio.pg_error;
--- linux-next.orig/include/linux/nfs_fs.h 2010-12-13 21:45:55.000000000 +0800
+++ linux-next/include/linux/nfs_fs.h 2010-12-13 21:46:20.000000000 +0800
@@ -216,7 +216,6 @@ struct nfs_inode {
#define NFS_INO_STALE (1) /* possible stale inode */
#define NFS_INO_ACL_LRU_SET (2) /* Inode is on the LRU list */
#define NFS_INO_MOUNTPOINT (3) /* inode is remote mountpoint */
-#define NFS_INO_FLUSHING (4) /* inode is flushing out data */
#define NFS_INO_FSCACHE (5) /* inode can be cached by FS-Cache */
#define NFS_INO_FSCACHE_LOCK (6) /* FS-Cache cookie management lock */
#define NFS_INO_COMMIT (7) /* inode is committing unstable writes */



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