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SubjectRe: [PATCH] improve the performance of large sequential write NFS workloads
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On Tue, 2009-12-22 at 09:59 +0800, Wu Fengguang wrote: 
> 1) normal fs sets I_DIRTY_DATASYNC when extending i_size, however NFS
> will set the flag for any pages written -- why this trick? To
> guarantee the call of nfs_commit_inode()? Which unfortunately turns
> almost every server side NFS write into sync writes..
>
> writeback_single_inode:
> do_writepages
> nfs_writepages
> nfs_writepage ----[short time later]---> nfs_writeback_release*
> nfs_mark_request_commit
> __mark_inode_dirty(I_DIRTY_DATASYNC);
>
> if (I_DIRTY_SYNC || I_DIRTY_DATASYNC) <---- so this will be true for most time
> write_inode
> nfs_write_inode
> nfs_commit_inode


I have been working on a fix for this. We basically do want to ensure
that NFS calls commit (otherwise we're not finished cleaning the dirty
pages), but we want to do it _after_ we've waited for all the writes to
complete. See below...

Trond

------------------------------------------------------------------------------------------------------
VFS: Add a new inode state: I_UNSTABLE_PAGES
From: Trond Myklebust <Trond.Myklebust@netapp.com>

Add a new inode state to enable the vfs to commit the nfs unstable pages to
stable storage once the write back of dirty pages is done.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
---
fs/fs-writeback.c | 24 ++++++++++++++++++++++--
fs/nfs/inode.c | 13 +++++--------
fs/nfs/write.c | 2 +-
include/linux/fs.h | 7 +++++++
4 files changed, 35 insertions(+), 11 deletions(-)

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 49bc1b8..c035efe 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -388,6 +388,14 @@ static int write_inode(struct inode *inode, int sync)
}

/*
+ * Commit the NFS unstable pages.
+ */
+static void commit_unstable_pages(struct inode *inode, int wait)
+{
+ return write_inode(inode, sync);
+}
+
+/*
* Wait for writeback on an inode to complete.
*/
static void inode_wait_for_writeback(struct inode *inode)
@@ -474,6 +482,18 @@ writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
}

spin_lock(&inode_lock);
+ /*
+ * Special state for cleaning NFS unstable pages
+ */
+ if (inode->i_state & I_UNSTABLE_PAGES) {
+ int err;
+ inode->i_state &= ~I_UNSTABLE_PAGES;
+ spin_unlock(&inode_lock);
+ err = commit_unstable_pages(inode, wait);
+ if (ret == 0)
+ ret = err;
+ spin_lock(&inode_lock);
+ }
inode->i_state &= ~I_SYNC;
if (!(inode->i_state & (I_FREEING | I_CLEAR))) {
if ((inode->i_state & I_DIRTY_PAGES) && wbc->for_kupdate) {
@@ -481,7 +501,7 @@ writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
* More pages get dirtied by a fast dirtier.
*/
goto select_queue;
- } else if (inode->i_state & I_DIRTY) {
+ } else if (inode->i_state & (I_DIRTY|I_UNSTABLE_PAGES)) {
/*
* At least XFS will redirty the inode during the
* writeback (delalloc) and on io completion (isize).
@@ -1050,7 +1070,7 @@ void __mark_inode_dirty(struct inode *inode, int flags)

spin_lock(&inode_lock);
if ((inode->i_state & flags) != flags) {
- const int was_dirty = inode->i_state & I_DIRTY;
+ const int was_dirty = inode->i_state & (I_DIRTY|I_UNSTABLE_PAGES);

inode->i_state |= flags;

diff --git a/fs/nfs/inode.c b/fs/nfs/inode.c
index faa0918..4f129b3 100644
--- a/fs/nfs/inode.c
+++ b/fs/nfs/inode.c
@@ -99,17 +99,14 @@ u64 nfs_compat_user_ino64(u64 fileid)

int nfs_write_inode(struct inode *inode, int sync)
{
+ int flags = 0;
int ret;

- if (sync) {
- ret = filemap_fdatawait(inode->i_mapping);
- if (ret == 0)
- ret = nfs_commit_inode(inode, FLUSH_SYNC);
- } else
- ret = nfs_commit_inode(inode, 0);
- if (ret >= 0)
+ if (sync)
+ flags = FLUSH_SYNC;
+ ret = nfs_commit_inode(inode, flags);
+ if (ret > 0)
return 0;
- __mark_inode_dirty(inode, I_DIRTY_DATASYNC);
return ret;
}

diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index d171696..2f74e44 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -441,7 +441,7 @@ nfs_mark_request_commit(struct nfs_page *req)
spin_unlock(&inode->i_lock);
inc_zone_page_state(req->wb_page, NR_UNSTABLE_NFS);
inc_bdi_stat(req->wb_page->mapping->backing_dev_info, BDI_RECLAIMABLE);
- __mark_inode_dirty(inode, I_DIRTY_DATASYNC);
+ mark_inode_unstable_pages(inode);
}

static int
diff --git a/include/linux/fs.h b/include/linux/fs.h
index cca1919..ab01af0 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1637,6 +1637,8 @@ struct super_operations {
#define I_CLEAR 64
#define __I_SYNC 7
#define I_SYNC (1 << __I_SYNC)
+#define __I_UNSTABLE_PAGES 9
+#define I_UNSTABLE_PAGES (1 << __I_UNSTABLE_PAGES)

#define I_DIRTY (I_DIRTY_SYNC | I_DIRTY_DATASYNC | I_DIRTY_PAGES)

@@ -1651,6 +1653,11 @@ static inline void mark_inode_dirty_sync(struct inode *inode)
__mark_inode_dirty(inode, I_DIRTY_SYNC);
}

+static inline void mark_inode_unstable_pages(struct inode *inode)
+{
+ __mark_inode_dirty(inode, I_UNSTABLE_PAGES);
+}
+
/**
* inc_nlink - directly increment an inode's link count
* @inode: inode


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