NFS: Fix a performance regression in readdir (79f687a3) · Commits · 戴 / test

Ben Coddington reports that commit , by adding the function nfs_dir_mapping_need_revalidate() that checks page cache validity on each call to nfs_readdir() causes a performance regression when the directory is being modified. If the directory is changing while we're iterating through the directory, POSIX does not require us to invalidate the page cache unless the user calls rewinddir(). However, we still do want to ensure that we use readdirplus in order to avoid a load of stat() calls when the user is doing an 'ls -l' workload. The fix should be to invalidate the page cache immediately when we're setting the NFS_INO_ADVISE_RDPLUS bit. Reported-by:

Benjamin Coddington <bcodding@redhat.com> Fixes: ("NFS: Be more aggressive in using readdirplus...") Reviewed-by:

Benjamin Coddington <bcodding@redhat.com> Tested-by:

Benjamin Coddington <bcodding@redhat.com> Signed-off-by:

Trond Myklebust <trond.myklebust@primarydata.com>

fs/nfs/dir.c

+2 −13

Original line number	Diff line number	Diff line
		@@ -477,7 +477,7 @@ void nfs_force_use_readdirplus(struct inode *dir)
		{
		if (!list_empty(&NFS_I(dir)->open_files)) {
		nfs_advise_use_readdirplus(dir);
		nfs_zap_mapping(dir, dir->i_mapping);
		invalidate_mapping_pages(dir->i_mapping, 0, -1);
		}
		}

		@@ -886,17 +886,6 @@ int uncached_readdir(nfs_readdir_descriptor_t *desc)
		goto out;
		}

		static bool nfs_dir_mapping_need_revalidate(struct inode *dir)
		{
		struct nfs_inode *nfsi = NFS_I(dir);

		if (nfs_attribute_cache_expired(dir))
		return true;
		if (nfsi->cache_validity & NFS_INO_INVALID_DATA)
		return true;
		return false;
		}

		/* The file offset position represents the dirent entry number. A
		last cookie cache takes care of the common case of reading the
		whole directory.
		@@ -928,7 +917,7 @@ static int nfs_readdir(struct file file, struct dir_context ctx)
		desc->decode = NFS_PROTO(inode)->decode_dirent;
		desc->plus = nfs_use_readdirplus(inode, ctx) ? 1 : 0;

		if (ctx->pos == 0 \|\| nfs_dir_mapping_need_revalidate(inode))
		if (ctx->pos == 0 \|\| nfs_attribute_cache_expired(inode))
		res = nfs_revalidate_mapping(inode, file->f_mapping);
		if (res < 0)
		goto out;

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