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NFS: avoid waiting at all in nfs_release_page when congested. 

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>
Acked-by: Jeff Layton <jlayton@primarydata.com>
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
This commit is contained in:
NeilBrown 2014-09-24 11:28:32 +10:00 committed by Trond Myklebust
parent 9590544694
commit 353db79662
2 changed files with 12 additions and 2 deletions
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9
fs/nfs/file.c
View File

@ -477,7 +477,8 @@ 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
@ -488,9 +489,13 @@ 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 */

5
fs/nfs/write.c
View File

@ -1611,6 +1611,7 @@ 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);
@ -1644,6 +1645,10 @@ 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));