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Gmane
From: Steve Rago <sar-a+KepyhlMvJWk0Htik3J/w <at> public.gmane.org>
Subject: [PATCH] improve the performance of large sequential write NFS workloads
Newsgroups: gmane.linux.nfs
Date: Thursday 17th December 2009 02:03:40 UTC (over 7 years ago)
Eager Writeback for NFS Clients
-------------------------------
Prevent applications that write large sequential streams of data (like
backup, for example)
from entering into a memory pressure state, which degrades performance by
falling back to
synchronous operations (both synchronous writes and additional commits). 
This is accomplished
by preventing the client application from dirtying pages faster than they
can be written to
the server: clients write pages eagerly instead of lazily.

The eager writeback is controlled by a sysctl: fs.nfs.nfs_max_woutstanding
set to 0 disables
the feature.  Otherwise it contains the maximum number of outstanding NFS
writes that can be
in flight for a given file.  This is used to block the application from
dirtying more pages
until the writes are complete.

This patch is based heavily (okay, almost entirely) on a prior patch by
Peter Staubach.  For
the original patch, see http://article.gmane.org/gmane.linux.nfs/24323.

The patch below applies to linux-2.6.32-rc7, but it should apply cleanly to
vanilla linux-2.6.32.

Performance data and tuning notes can be found on my web site (http://www.nec-labs.com/~sar).
With iozone, I see about 50% improvement for large sequential write
workloads over a 1Gb Ethernet.
With an in-house micro-benchmark, I see 80% improvement for large,
single-stream, sequential
workloads (where "large" is defined to be greater than the memory size on
the client).

Signed-off-by: Steve Rago 
---

diff -rupN -X linux-2.6.32-rc7/Documentation/dontdiff
linux-2.6.32-rc7-orig/fs/fs-writeback.c linux-2.6.32-rc7/fs/fs-writeback.c
--- linux-2.6.32-rc7-orig/fs/fs-writeback.c	2009-11-12 19:46:07.000000000
-0500
+++ linux-2.6.32-rc7/fs/fs-writeback.c	2009-11-30 15:36:30.735453450 -0500
@@ -771,6 +771,8 @@ static long wb_writeback(struct bdi_writ
 		wbc.range_start = 0;
 		wbc.range_end = LLONG_MAX;
 	}
+	if (args->for_background || wbc.for_kupdate)
+		wbc.nonblocking = 1;
 
 	for (;;) {
 		/*
@@ -859,6 +861,8 @@ static long wb_check_old_data_flush(stru
 	unsigned long expired;
 	long nr_pages;
 
+	if (dirty_writeback_interval == 0)
+		return 0;
 	expired = wb->last_old_flush +
 			msecs_to_jiffies(dirty_writeback_interval * 10);
 	if (time_before(jiffies, expired))
@@ -954,7 +958,11 @@ int bdi_writeback_task(struct bdi_writeb
 				break;
 		}
 
-		wait_jiffies = msecs_to_jiffies(dirty_writeback_interval * 10);
+		if (dirty_writeback_interval == 0)
+			wait_jiffies = msecs_to_jiffies(5000);	/* default */
+		else
+			wait_jiffies =
+				msecs_to_jiffies(dirty_writeback_interval * 10);
 		schedule_timeout_interruptible(wait_jiffies);
 		try_to_freeze();
 	}
diff -rupN -X linux-2.6.32-rc7/Documentation/dontdiff
linux-2.6.32-rc7-orig/fs/nfs/file.c linux-2.6.32-rc7/fs/nfs/file.c
--- linux-2.6.32-rc7-orig/fs/nfs/file.c	2009-11-12 19:46:07.000000000 -0500
+++ linux-2.6.32-rc7/fs/nfs/file.c	2009-11-30 15:21:22.635101295 -0500
@@ -589,11 +589,17 @@ static int nfs_need_sync_write(struct fi
 	return 0;
 }
 
+static int nfs_is_seqwrite(struct inode *inode, loff_t pos)
+{
+	return NFS_I(inode)->wrpos == pos;
+}
+
 static ssize_t nfs_file_write(struct kiocb *iocb, const struct iovec *iov,
 				unsigned long nr_segs, loff_t pos)
 {
 	struct dentry * dentry = iocb->ki_filp->f_path.dentry;
 	struct inode * inode = dentry->d_inode;
+	struct nfs_inode *nfsi = NFS_I(inode);
 	ssize_t result;
 	size_t count = iov_length(iov, nr_segs);
 
@@ -607,6 +613,12 @@ static ssize_t nfs_file_write(struct kio
 	result = -EBUSY;
 	if (IS_SWAPFILE(inode))
 		goto out_swapfile;
+
+	result = count;
+	if (!count)
+		goto out;
+	nfs_wait_woutstanding(inode);
+
 	/*
 	 * O_APPEND implies that we must revalidate the file length.
 	 */
@@ -623,10 +635,21 @@ static ssize_t nfs_file_write(struct kio
 	nfs_add_stats(inode, NFSIOS_NORMALWRITTENBYTES, count);
 	result = generic_file_aio_write(iocb, iov, nr_segs, pos);
 	/* Return error values for O_SYNC and IS_SYNC() */
-	if (result >= 0 && nfs_need_sync_write(iocb->ki_filp, inode)) {
-		int err = nfs_do_fsync(nfs_file_open_context(iocb->ki_filp), inode);
-		if (err < 0)
-			result = err;
+	if (result >= 0) {
+		if (nfs_need_sync_write(iocb->ki_filp, inode)) {
+			int err;
+
+			err = nfs_do_fsync(nfs_file_open_context(iocb->ki_filp),
+					   inode);
+			if (err < 0)
+				result = err;
+		} else if (nfs_max_woutstanding != 0 &&
+		     nfs_is_seqwrite(inode, pos) &&
+		     atomic_read(&nfsi->ndirty) >= NFS_SERVER(inode)->wpages) {
+			nfs_wb_eager(inode);
+		}
+		if (result > 0)
+			nfsi->wrpos = pos + result;
 	}
 out:
 	return result;
diff -rupN -X linux-2.6.32-rc7/Documentation/dontdiff
linux-2.6.32-rc7-orig/fs/nfs/inode.c linux-2.6.32-rc7/fs/nfs/inode.c
--- linux-2.6.32-rc7-orig/fs/nfs/inode.c	2009-11-12 19:46:07.000000000
-0500
+++ linux-2.6.32-rc7/fs/nfs/inode.c	2009-11-13 11:36:43.888410914 -0500
@@ -508,7 +508,9 @@ void nfs_setattr_update_inode(struct ino
 int nfs_getattr(struct vfsmount *mnt, struct dentry *dentry, struct kstat
*stat)
 {
 	struct inode *inode = dentry->d_inode;
-	int need_atime = NFS_I(inode)->cache_validity & NFS_INO_INVALID_ATIME;
+	struct nfs_inode *nfsi = NFS_I(inode);
+	int need_atime = nfsi->cache_validity & NFS_INO_INVALID_ATIME;
+	int woutstanding = nfs_max_woutstanding;
 	int err;
 
 	/*
@@ -519,9 +521,8 @@ int nfs_getattr(struct vfsmount *mnt, st
 	 * nfs_wb_nocommit.
 	 */
 	if (S_ISREG(inode->i_mode)) {
-		mutex_lock(&inode->i_mutex);
+		atomic_add(woutstanding, &nfsi->writes);
 		nfs_wb_nocommit(inode);
-		mutex_unlock(&inode->i_mutex);
 	}
 
 	/*
@@ -545,6 +546,11 @@ int nfs_getattr(struct vfsmount *mnt, st
 		generic_fillattr(inode, stat);
 		stat->ino = nfs_compat_user_ino64(NFS_FILEID(inode));
 	}
+
+	if (S_ISREG(inode->i_mode)) {
+		atomic_sub(woutstanding, &nfsi->writes);
+		wake_up(&nfsi->writes_wq);
+	}
 	return err;
 }
 
@@ -1418,9 +1424,13 @@ static void init_once(void *foo)
 	INIT_LIST_HEAD(&nfsi->access_cache_inode_lru);
 	INIT_RADIX_TREE(&nfsi->nfs_page_tree, GFP_ATOMIC);
 	nfsi->npages = 0;
+	atomic_set(&nfsi->ndirty, 0);
 	atomic_set(&nfsi->silly_count, 1);
 	INIT_HLIST_HEAD(&nfsi->silly_list);
 	init_waitqueue_head(&nfsi->waitqueue);
+	atomic_set(&nfsi->writes, 0);
+	init_waitqueue_head(&nfsi->writes_wq);
+	nfsi->wrpos = 0;
 	nfs4_init_once(nfsi);
 }
 
diff -rupN -X linux-2.6.32-rc7/Documentation/dontdiff
linux-2.6.32-rc7-orig/fs/nfs/sysctl.c linux-2.6.32-rc7/fs/nfs/sysctl.c
--- linux-2.6.32-rc7-orig/fs/nfs/sysctl.c	2009-11-12 19:46:07.000000000
-0500
+++ linux-2.6.32-rc7/fs/nfs/sysctl.c	2009-11-13 11:36:43.895459044 -0500
@@ -58,6 +58,14 @@ static ctl_table nfs_cb_sysctls[] = {
 		.mode		= 0644,
 		.proc_handler	= &proc_dointvec,
 	},
+	{
+		.ctl_name       = CTL_UNNUMBERED,
+		.procname       = "nfs_max_woutstanding",
+		.data           = &nfs_max_woutstanding,
+		.maxlen         = sizeof(int),
+		.mode           = 0644,
+		.proc_handler   = &proc_dointvec,
+	},
 	{ .ctl_name = 0 }
 };
 
diff -rupN -X linux-2.6.32-rc7/Documentation/dontdiff
linux-2.6.32-rc7-orig/fs/nfs/write.c linux-2.6.32-rc7/fs/nfs/write.c
--- linux-2.6.32-rc7-orig/fs/nfs/write.c	2009-11-12 19:46:07.000000000
-0500
+++ linux-2.6.32-rc7/fs/nfs/write.c	2009-12-08 13:26:35.416629518 -0500
@@ -176,6 +176,8 @@ static void nfs_mark_uptodate(struct pag
 
 static int wb_priority(struct writeback_control *wbc)
 {
+	if (nfs_max_woutstanding != 0)
+		return 0;
 	if (wbc->for_reclaim)
 		return FLUSH_HIGHPRI | FLUSH_STABLE;
 	if (wbc->for_kupdate)
@@ -200,7 +202,9 @@ static int nfs_set_page_writeback(struct
 	if (!ret) {
 		struct inode *inode = page->mapping->host;
 		struct nfs_server *nfss = NFS_SERVER(inode);
+		struct nfs_inode *nfsi = NFS_I(inode);
 
+		atomic_dec(&nfsi->ndirty);
 		if (atomic_long_inc_return(&nfss->writeback) >
 				NFS_CONGESTION_ON_THRESH) {
 			set_bdi_congested(&nfss->backing_dev_info,
@@ -325,6 +329,39 @@ static int nfs_writepages_callback(struc
 	return ret;
 }
 
+int nfs_max_woutstanding = 16;
+
+static void nfs_inc_woutstanding(struct inode *inode)
+{
+	struct nfs_inode *nfsi = NFS_I(inode);
+	atomic_inc(&nfsi->writes);
+}
+
+static void nfs_dec_woutstanding(struct inode *inode)
+{
+	struct nfs_inode *nfsi = NFS_I(inode);
+	if (atomic_dec_return(&nfsi->writes) < nfs_max_woutstanding)
+		wake_up(&nfsi->writes_wq);
+}
+
+void nfs_wait_woutstanding(struct inode *inode)
+{
+	if (nfs_max_woutstanding != 0) {
+		unsigned long background_thresh;
+		unsigned long dirty_thresh;
+		long npages;
+		struct nfs_inode *nfsi = NFS_I(inode);
+
+		get_dirty_limits(&background_thresh, &dirty_thresh, NULL, NULL);
+		npages = global_page_state(NR_FILE_DIRTY) +
+			 global_page_state(NR_UNSTABLE_NFS) +
+			 global_page_state(NR_WRITEBACK);
+		if (npages >= background_thresh)
+			wait_event(nfsi->writes_wq,
+			   atomic_read(&nfsi->writes) < nfs_max_woutstanding);
+	}
+}
+
 int nfs_writepages(struct address_space *mapping, struct writeback_control
*wbc)
 {
 	struct inode *inode = mapping->host;
@@ -420,6 +457,9 @@ static void nfs_inode_remove_request(str
 static void
 nfs_mark_request_dirty(struct nfs_page *req)
 {
+	struct inode *inode = req->wb_context->path.dentry->d_inode;
+	struct nfs_inode *nfsi = NFS_I(inode);
+	atomic_inc(&nfsi->ndirty);
 	__set_page_dirty_nobuffers(req->wb_page);
 }
 
@@ -682,16 +722,18 @@ static struct nfs_page * nfs_setup_write
 
 	req = nfs_try_to_update_request(inode, page, offset, bytes);
 	if (req != NULL)
-		goto out;
+		return req;
 	req = nfs_create_request(ctx, inode, page, offset, bytes);
 	if (IS_ERR(req))
-		goto out;
+		return req;
 	error = nfs_inode_add_request(inode, req);
 	if (error != 0) {
 		nfs_release_request(req);
 		req = ERR_PTR(error);
+	} else {
+		struct nfs_inode *nfsi = NFS_I(inode);
+		atomic_inc(&nfsi->ndirty);
 	}
-out:
 	return req;
 }
 
@@ -877,6 +919,7 @@ static int nfs_write_rpcsetup(struct nfs
 		count,
 		(unsigned long long)data->args.offset);
 
+	nfs_inc_woutstanding(inode);
 	task = rpc_run_task(&task_setup_data);
 	if (IS_ERR(task))
 		return PTR_ERR(task);
@@ -1172,7 +1215,7 @@ int nfs_writeback_done(struct rpc_task *
 	 */
 	status = NFS_PROTO(data->inode)->write_done(task, data);
 	if (status != 0)
-		return status;
+		goto out;
 	nfs_add_stats(data->inode, NFSIOS_SERVERWRITTENBYTES, resp->count);
 
 #if defined(CONFIG_NFS_V3) || defined(CONFIG_NFS_V4)
@@ -1229,6 +1272,8 @@ int nfs_writeback_done(struct rpc_task *
 		task->tk_status = -EIO;
 	}
 	nfs4_sequence_free_slot(server->nfs_client, &data->res.seq_res);
+out:
+	nfs_dec_woutstanding(data->inode);
 	return 0;
 }
 
@@ -1591,6 +1636,24 @@ int nfs_wb_page(struct inode *inode, str
 	return nfs_wb_page_priority(inode, page, FLUSH_STABLE);
 }
 
+int nfs_wb_eager(struct inode *inode)
+{
+	struct address_space *mapping = inode->i_mapping;
+	struct writeback_control wbc = {
+		.bdi            = mapping->backing_dev_info,
+		.sync_mode      = WB_SYNC_NONE,
+		.nr_to_write    = LONG_MAX,
+		.range_start    = 0,
+		.range_end      = LLONG_MAX,
+	};
+	int ret;
+
+	ret = nfs_writepages(mapping, &wbc);
+	if (ret < 0)
+		__mark_inode_dirty(inode, I_DIRTY_PAGES);
+	return ret;
+}
+
 #ifdef CONFIG_MIGRATION
 int nfs_migrate_page(struct address_space *mapping, struct page *newpage,
 		struct page *page)
@@ -1674,4 +1737,3 @@ void nfs_destroy_writepagecache(void)
 	mempool_destroy(nfs_wdata_mempool);
 	kmem_cache_destroy(nfs_wdata_cachep);
 }
-
diff -rupN -X linux-2.6.32-rc7/Documentation/dontdiff
linux-2.6.32-rc7-orig/include/linux/nfs_fs.h
linux-2.6.32-rc7/include/linux/nfs_fs.h
--- linux-2.6.32-rc7-orig/include/linux/nfs_fs.h	2009-11-12
19:46:07.000000000 -0500
+++ linux-2.6.32-rc7/include/linux/nfs_fs.h	2009-11-13 11:36:43.982136105
-0500
@@ -166,6 +166,7 @@ struct nfs_inode {
 	struct radix_tree_root	nfs_page_tree;
 
 	unsigned long		npages;
+	atomic_t		ndirty;
 
 	/* Open contexts for shared mmap writes */
 	struct list_head	open_files;
@@ -187,6 +188,11 @@ struct nfs_inode {
 #ifdef CONFIG_NFS_FSCACHE
 	struct fscache_cookie	*fscache;
 #endif
+
+	loff_t			wrpos;
+	atomic_t		writes;
+	wait_queue_head_t	writes_wq;
+
 	struct inode		vfs_inode;
 };
 
@@ -467,11 +473,13 @@ extern void nfs_unblock_sillyrename(stru
  * linux/fs/nfs/write.c
  */
 extern int  nfs_congestion_kb;
+extern int  nfs_max_woutstanding;
 extern int  nfs_writepage(struct page *page, struct writeback_control
*wbc);
 extern int  nfs_writepages(struct address_space *, struct
writeback_control *);
 extern int  nfs_flush_incompatible(struct file *file, struct page *page);
 extern int  nfs_updatepage(struct file *, struct page *, unsigned int,
unsigned int);
 extern int nfs_writeback_done(struct rpc_task *, struct nfs_write_data *);
+extern void nfs_wait_woutstanding(struct inode *);
 
 /*
  * Try to write back everything synchronously (but check the
@@ -482,6 +490,7 @@ extern int nfs_wb_all(struct inode *inod
 extern int nfs_wb_nocommit(struct inode *inode);
 extern int nfs_wb_page(struct inode *inode, struct page* page);
 extern int nfs_wb_page_cancel(struct inode *inode, struct page* page);
+extern int nfs_wb_eager(struct inode *inode);
 #if defined(CONFIG_NFS_V3) || defined(CONFIG_NFS_V4)
 extern int  nfs_commit_inode(struct inode *, int);
 extern struct nfs_write_data *nfs_commitdata_alloc(void);
diff -rupN -X linux-2.6.32-rc7/Documentation/dontdiff
linux-2.6.32-rc7-orig/mm/page-writeback.c
linux-2.6.32-rc7/mm/page-writeback.c
--- linux-2.6.32-rc7-orig/mm/page-writeback.c	2009-11-12 19:46:07.000000000
-0500
+++ linux-2.6.32-rc7/mm/page-writeback.c	2009-11-18 10:05:22.314373138
-0500
@@ -536,7 +536,7 @@ static void balance_dirty_pages(struct a
 		 * threshold otherwise wait until the disk writes catch
 		 * up.
 		 */
-		if (bdi_nr_reclaimable > bdi_thresh) {
+		if (bdi_nr_reclaimable != 0) {
 			writeback_inodes_wbc(&wbc);
 			pages_written += write_chunk - wbc.nr_to_write;
 			get_dirty_limits(&background_thresh, &dirty_thresh,


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