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Date: Mon, 5 Oct 2009 15:10:26 +0800
From: Wu Fengguang <fengguang.wu@...el.com>
To: "jens.axboe@...cle.com" <jens.axboe@...cle.com>
Cc: Chris Mason <chris.mason@...cle.com>,
Trond Myklebust <Trond.Myklebust@...app.com>,
Andrew Morton <akpm@...ux-foundation.org>,
linux-fsdevel@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
linux-nfs@...r.kernel.org
Subject: [PATCH v2] NFS: introduce writeback wait queue
Hi all,
This version makes two standalone functions for easier reuse.
Before patch, nr_writeback is near 1G on my 2GB laptop:
nr_writeback nr_dirty nr_unstable
203994 2 154469
203994 2 154469
After patch, nr_writeback is limited to nfs_congestion_kb=42MB.
nr_writeback nr_dirty nr_unstable
11180 34195 11754
9865 36821 8234
10137 36695 9338
One minor problem I noticed is, NFS writeback is not very smooth.
This per 0.1s sampled trace shows that it can sometimes stuck for
up to 0.5s:
nr_writeback nr_dirty nr_unstable
11055 37408 9599
10311 37315 10529
10869 35920 11459
10869 35920 11459
10869 35920 11459
10869 35920 11459
10869 35920 11459
10838 35891 10042
10466 35891 10414
10900 34744 11437
10249 34744 12088
10249 34744 12088
10249 34744 12088
10249 34744 12088
10249 34744 12088
10249 34744 12088
10133 34743 10663
10505 34743 11035
10970 34991 11345
10691 34991 11593
10691 34991 11593
10691 34991 11593
10691 34991 11593
10691 34991 11593
Trond, I guess nr_writeback/nr_unstable are decreased in async RPC
"complete" events. It is understandable that nr_dirty can sometimes
stuck on local waits, but the "local determined" nr_dirty and "remote
determined" nr_writeback/nr_unstable tend to stuck at the same time?
Did I miss something (that could be obvious to you)?
Thanks,
Fengguang
---
Subject: NFS: introduce writeback wait queue
The generic writeback routines are departing from congestion_wait()
in preferance of get_request_wait(), aka. waiting on the block queues.
Introduce the missing writeback wait queue for NFS, otherwise its
writeback pages will grow out of control.
CC: Jens Axboe <jens.axboe@...cle.com>
CC: Chris Mason <chris.mason@...cle.com>
CC: Trond Myklebust <Trond.Myklebust@...app.com>
Signed-off-by: Wu Fengguang <fengguang.wu@...el.com>
---
fs/nfs/client.c | 2
fs/nfs/write.c | 86 ++++++++++++++++++++++++++++--------
include/linux/nfs_fs_sb.h | 1
3 files changed, 72 insertions(+), 17 deletions(-)
--- linux.orig/fs/nfs/write.c 2009-10-05 13:27:20.000000000 +0800
+++ linux/fs/nfs/write.c 2009-10-05 14:48:39.000000000 +0800
@@ -189,24 +189,72 @@ static int wb_priority(struct writeback_
int nfs_congestion_kb;
-#define NFS_CONGESTION_ON_THRESH (nfs_congestion_kb >> (PAGE_SHIFT-10))
-#define NFS_CONGESTION_OFF_THRESH \
- (NFS_CONGESTION_ON_THRESH - (NFS_CONGESTION_ON_THRESH >> 2))
+/*
+ * SYNC requests will be blocked on (2*limit) and wakeup on (2*limit - limit/8)
+ * ASYNC requests will be blocked on (limit) and wakeup on (limit - limit/8)
+ * In this way SYNC writes will never be blocked by ASYNC ones.
+ */
-static int nfs_set_page_writeback(struct page *page)
+static void nfs_writeback_wait(atomic_long_t *nr, long limit, int is_sync,
+ struct backing_dev_info *bdi,
+ wait_queue_head_t *wqh)
{
- int ret = test_set_page_writeback(page);
+ DEFINE_WAIT(wait);
+ int hard_limit = limit * 2;
- if (!ret) {
- struct inode *inode = page->mapping->host;
- struct nfs_server *nfss = NFS_SERVER(inode);
+ if (atomic_long_read(nr) <= limit)
+ return;
+
+ set_bdi_congested(bdi, BLK_RW_ASYNC);
- if (atomic_long_inc_return(&nfss->writeback) >
- NFS_CONGESTION_ON_THRESH) {
- set_bdi_congested(&nfss->backing_dev_info,
- BLK_RW_ASYNC);
+ if (is_sync && atomic_long_read(nr) <= hard_limit)
+ return;
+
+ for (;;) {
+ prepare_to_wait(&wqh[is_sync], &wait, TASK_UNINTERRUPTIBLE);
+
+ io_schedule();
+
+ if (atomic_long_read(nr) <= limit - limit/8)
+ break;
+ if (is_sync && atomic_long_read(nr) <= hard_limit - limit/8)
+ break;
+ }
+ finish_wait(&wqh[is_sync], &wait);
+}
+
+static void nfs_writeback_wakeup(long nr, long limit,
+ struct backing_dev_info *bdi,
+ wait_queue_head_t *wqh)
+{
+ int hard_limit = limit * 2;
+
+ if (nr < hard_limit - limit/8) {
+ if (waitqueue_active(&wqh[BLK_RW_SYNC]))
+ wake_up(&wqh[BLK_RW_SYNC]);
+ if (nr < limit - limit/8) {
+ clear_bdi_congested(bdi, BLK_RW_ASYNC);
+ if (waitqueue_active(&wqh[BLK_RW_ASYNC]))
+ wake_up(&wqh[BLK_RW_ASYNC]);
}
}
+}
+
+static int nfs_set_page_writeback(struct page *page,
+ struct writeback_control *wbc)
+{
+ struct inode *inode = page->mapping->host;
+ struct nfs_server *nfss = NFS_SERVER(inode);
+ int ret = test_set_page_writeback(page);
+
+ if (!ret) {
+ atomic_long_inc(&nfss->writeback);
+ nfs_writeback_wait(&nfss->writeback,
+ nfs_congestion_kb >> (PAGE_SHIFT-10),
+ wbc->sync_mode == WB_SYNC_ALL,
+ &nfss->backing_dev_info,
+ nfss->writeback_wait);
+ }
return ret;
}
@@ -216,8 +264,11 @@ static void nfs_end_page_writeback(struc
struct nfs_server *nfss = NFS_SERVER(inode);
end_page_writeback(page);
- if (atomic_long_dec_return(&nfss->writeback) < NFS_CONGESTION_OFF_THRESH)
- clear_bdi_congested(&nfss->backing_dev_info, BLK_RW_ASYNC);
+
+ nfs_writeback_wakeup(atomic_long_dec_return(&nfss->writeback),
+ nfs_congestion_kb >> (PAGE_SHIFT-10),
+ &nfss->backing_dev_info,
+ nfss->writeback_wait);
}
static struct nfs_page *nfs_find_and_lock_request(struct page *page)
@@ -254,7 +305,8 @@ static struct nfs_page *nfs_find_and_loc
* May return an error if the user signalled nfs_wait_on_request().
*/
static int nfs_page_async_flush(struct nfs_pageio_descriptor *pgio,
- struct page *page)
+ struct page *page,
+ struct writeback_control *wbc)
{
struct nfs_page *req;
int ret = 0;
@@ -266,7 +318,7 @@ static int nfs_page_async_flush(struct n
if (IS_ERR(req))
goto out;
- ret = nfs_set_page_writeback(page);
+ ret = nfs_set_page_writeback(page, wbc);
BUG_ON(ret != 0);
BUG_ON(test_bit(PG_CLEAN, &req->wb_flags));
@@ -286,7 +338,7 @@ static int nfs_do_writepage(struct page
nfs_add_stats(inode, NFSIOS_WRITEPAGES, 1);
nfs_pageio_cond_complete(pgio, page->index);
- return nfs_page_async_flush(pgio, page);
+ return nfs_page_async_flush(pgio, page, wbc);
}
/*
--- linux.orig/include/linux/nfs_fs_sb.h 2009-10-05 13:27:20.000000000 +0800
+++ linux/include/linux/nfs_fs_sb.h 2009-10-05 13:28:31.000000000 +0800
@@ -108,6 +108,7 @@ struct nfs_server {
struct nfs_iostats * io_stats; /* I/O statistics */
struct backing_dev_info backing_dev_info;
atomic_long_t writeback; /* number of writeback pages */
+ wait_queue_head_t writeback_wait[2];
int flags; /* various flags */
unsigned int caps; /* server capabilities */
unsigned int rsize; /* read size */
--- linux.orig/fs/nfs/client.c 2009-10-05 13:27:20.000000000 +0800
+++ linux/fs/nfs/client.c 2009-10-05 13:28:31.000000000 +0800
@@ -991,6 +991,8 @@ static struct nfs_server *nfs_alloc_serv
INIT_LIST_HEAD(&server->master_link);
atomic_set(&server->active, 0);
+ init_waitqueue_head(&server->writeback_wait[BLK_RW_SYNC]);
+ init_waitqueue_head(&server->writeback_wait[BLK_RW_ASYNC]);
server->io_stats = nfs_alloc_iostats();
if (!server->io_stats) {
--
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