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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>
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9590544694
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2 changed files with 12 additions and 2 deletions
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@ -477,7 +477,8 @@ static int nfs_release_page(struct page *page, gfp_t gfp)
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/* Always try to initiate a 'commit' if relevant, but only
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* wait for it if __GFP_WAIT is set and the calling process is
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* allowed to block. Even then, only wait 1 second.
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* allowed to block. Even then, only wait 1 second and only
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* if the 'bdi' is not congested.
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* Waiting indefinitely can cause deadlocks when the NFS
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* server is on this machine, and there is no particular need
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* to wait extensively here. A short wait has the benefit
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@ -488,9 +489,13 @@ static int nfs_release_page(struct page *page, gfp_t gfp)
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nfs_commit_inode(mapping->host, 0);
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if ((gfp & __GFP_WAIT) &&
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!current_is_kswapd() &&
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!(current->flags & PF_FSTRANS)) {
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!(current->flags & PF_FSTRANS) &&
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!bdi_write_congested(&nfss->backing_dev_info)) {
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wait_on_page_bit_killable_timeout(page, PG_private,
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HZ);
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if (PagePrivate(page))
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set_bdi_congested(&nfss->backing_dev_info,
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BLK_RW_ASYNC);
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}
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}
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/* If PagePrivate() is set, then the page is not freeable */
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@ -1611,6 +1611,7 @@ static void nfs_commit_release_pages(struct nfs_commit_data *data)
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struct nfs_page *req;
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int status = data->task.tk_status;
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struct nfs_commit_info cinfo;
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struct nfs_server *nfss;
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while (!list_empty(&data->pages)) {
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req = nfs_list_entry(data->pages.next);
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@ -1644,6 +1645,10 @@ static void nfs_commit_release_pages(struct nfs_commit_data *data)
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next:
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nfs_unlock_and_release_request(req);
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}
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nfss = NFS_SERVER(data->inode);
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if (atomic_long_read(&nfss->writeback) < NFS_CONGESTION_OFF_THRESH)
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clear_bdi_congested(&nfss->backing_dev_info, BLK_RW_ASYNC);
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nfs_init_cinfo(&cinfo, data->inode, data->dreq);
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if (atomic_dec_and_test(&cinfo.mds->rpcs_out))
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nfs_commit_clear_lock(NFS_I(data->inode));
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