[PATCH 4/5] NFS: avoid waiting at all in nfs_release_page when congested.

NeilBrown
2014-09-24T02:03:42Z

If nfs_release_page() is called on a sequence of pages which are all
in the same file which is blocked on COMMIT, each page could
contribute a 1 second delay which could be come excessive. I have
seen delays of as much as 208 seconds.

To keep the delay to one second, mark the bdi as write-congested
if the commit didn't finished. Once it does finish, the
write-congested flag will be cleared by nfs_commit_release_pages().

With this, the longest total delay in try_to_free_pages that I have
seen is under 3 seconds. With no waiting in nfs_release_page at all
I have seen delays of nearly 1.5 seconds.

Signed-off-by: NeilBrown <neilb@suse.de>
---
fs/nfs/file.c | 9 +++++++--
fs/nfs/write.c | 5 +++++
2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/fs/nfs/file.c b/fs/nfs/file.c
index ef5513322cf6..1243a15438d0 100644
--- a/fs/nfs/file.c
+++ b/fs/nfs/file.c
@@ -470,7 +470,8 @@ static int nfs_release_page(struct page *page, gfp_t gfp)

/* Always try to initiate a 'commit' if relevant, but only
* wait for it if __GFP_WAIT is set and the calling process is
- * allowed to block. Even then, only wait 1 second.
+ * allowed to block. Even then, only wait 1 second and only
+ * if the 'bdi' is not congested.
* Waiting indefinitely can cause deadlocks when the NFS
* server is on this machine, and there is no particular need
* to wait extensively here. A short wait has the benefit
@@ -481,9 +482,13 @@ static int nfs_release_page(struct page *page, gfp_t gfp)
nfs_commit_inode(mapping->host, 0);
if ((gfp & __GFP_WAIT) &&
!current_is_kswapd() &&
- !(current->flags & PF_FSTRANS)) {
+ !(current->flags & PF_FSTRANS) &&
+ !bdi_write_congested(&nfss->backing_dev_info)) {
wait_on_page_bit_killable_timeout(page, PG_private,
HZ);
+ if (PagePrivate(page))
+ set_bdi_congested(&nfss->backing_dev_info,
+ BLK_RW_ASYNC);
}
}
/* If PagePrivate() is set, then the page is not freeable */
diff --git a/fs/nfs/write.c b/fs/nfs/write.c
index b5d83c7545d4..3066c7fcb565 100644
--- a/fs/nfs/write.c
+++ b/fs/nfs/write.c
@@ -1638,6 +1638,7 @@ static void nfs_commit_release_pages(struct nfs_commit_data *data)
struct nfs_page *req;
int status = data->task.tk_status;
struct nfs_commit_info cinfo;
+ struct nfs_server *nfss;

while (!list_empty(&data->pages)) {
req = nfs_list_entry(data->pages.next);
@@ -1671,6 +1672,10 @@ static void nfs_commit_release_pages(struct nfs_commit_data *data)
next:
nfs_unlock_and_release_request(req);
}
+ nfss = NFS_SERVER(data->inode);
+ if (atomic_long_read(&nfss->writeback) < NFS_CONGESTION_OFF_THRESH)
+ clear_bdi_congested(&nfss->backing_dev_info, BLK_RW_ASYNC);
+
nfs_init_cinfo(&cinfo, data->inode, data->dreq);
if (atomic_dec_and_test(&cinfo.mds->rpcs_out))
nfs_commit_clear_lock(NFS_I(data->inode));