From 794092c57f89c2c833da00f82f38a0afcb4033bc Mon Sep 17 00:00:00 2001 From: Trond Myklebust Date: Fri, 6 Nov 2020 20:47:05 -0500 Subject: [PATCH] NFS: Do uncached readdir when we're seeking a cookie in an empty page cache If the directory is changing, causing the page cache to get invalidated while we are listing the contents, then the NFS client is currently forced to read in the entire directory contents from scratch, because it needs to perform a linear search for the readdir cookie. While this is not an issue for small directories, it does not scale to directories with millions of entries. In order to be able to deal with large directories that are changing, add a heuristic to ensure that if the page cache is empty, and we are searching for a cookie that is not the zero cookie, we just default to performing uncached readdir. Signed-off-by: Trond Myklebust Reviewed-by: Benjamin Coddington Tested-by: Benjamin Coddington Tested-by: Dave Wysochanski --- fs/nfs/dir.c | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c index 93c6f22cdc62..3f70697729d8 100644 --- a/fs/nfs/dir.c +++ b/fs/nfs/dir.c @@ -937,11 +937,28 @@ static int find_and_lock_cache_page(struct nfs_readdir_descriptor *desc) return res; } +static bool nfs_readdir_dont_search_cache(struct nfs_readdir_descriptor *desc) +{ + struct address_space *mapping = desc->file->f_mapping; + struct inode *dir = file_inode(desc->file); + unsigned int dtsize = NFS_SERVER(dir)->dtsize; + loff_t size = i_size_read(dir); + + /* + * Default to uncached readdir if the page cache is empty, and + * we're looking for a non-zero cookie in a large directory. + */ + return desc->dir_cookie != 0 && mapping->nrpages == 0 && size > dtsize; +} + /* Search for desc->dir_cookie from the beginning of the page cache */ static int readdir_search_pagecache(struct nfs_readdir_descriptor *desc) { int res; + if (nfs_readdir_dont_search_cache(desc)) + return -EBADCOOKIE; + do { if (desc->page_index == 0) { desc->current_index = 0;