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Commit 353db796 authored by NeilBrown's avatar NeilBrown Committed by Trond Myklebust
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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: default avatarNeilBrown <neilb@suse.de>
Acked-by: default avatarJeff Layton <jlayton@primarydata.com>
Signed-off-by: default avatarTrond Myklebust <trond.myklebust@primarydata.com>
parent 95905446

fs/nfs/file.c

+7 −2
Original line number Diff line number Diff line
@@ -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 */

fs/nfs/write.c

+5 −0
Original line number Diff line number Diff line
@@ -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));