Commit 2be4f05a authored by Chuck Lever's avatar Chuck Lever Committed by Christian Brauner
Browse files

libfs: Remove parent dentry locking in offset_iterate_dir() 



Since offset_iterate_dir() does not walk the parent's d_subdir list
nor does it manipulate the parent's d_child, there doesn't seem to
be a reason to hold the parent's d_lock. The offset_ctx's xarray can
be sufficiently protected with just the RCU read lock.

Flame graph data captured during the git regression run shows a
20% reduction in CPU cycles consumed in offset_find_next().

Reported-by: default avatarkernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202307171640.e299f8d5-oliver.sang@intel.com


Signed-off-by: default avatarChuck Lever <chuck.lever@oracle.com>
Message-Id: <169030957098.157536.9938425508695693348.stgit@manet.1015granger.net>
Signed-off-by: default avatarChristian Brauner <brauner@kernel.org>
parent bbaef797

fs/libfs.c

+4 −7
Original line number Diff line number Diff line
@@ -407,7 +407,7 @@ static struct dentry *offset_find_next(struct xa_state *xas) 
	child = xas_next_entry(xas, U32_MAX);

	if (!child)

		goto out;

	spin_lock_nested(&child->d_lock, DENTRY_D_LOCK_NESTED);

	spin_lock(&child->d_lock);

	if (simple_positive(child))

		found = dget_dlock(child);

	spin_unlock(&child->d_lock);
@@ -425,17 +425,14 @@ static bool offset_dir_emit(struct dir_context *ctx, struct dentry *dentry) 
			  inode->i_ino, fs_umode_to_dtype(inode->i_mode));

}



static void offset_iterate_dir(struct dentry *dir, struct dir_context *ctx)

static void offset_iterate_dir(struct inode *inode, struct dir_context *ctx)

{

	struct inode *inode = d_inode(dir);

	struct offset_ctx *so_ctx = inode->i_op->get_offset_ctx(inode);

	XA_STATE(xas, &so_ctx->xa, ctx->pos);

	struct dentry *dentry;



	while (true) {

		spin_lock(&dir->d_lock);

		dentry = offset_find_next(&xas);

		spin_unlock(&dir->d_lock);

		if (!dentry)

			break;
@@ -465,7 +462,7 @@ static void offset_iterate_dir(struct dentry *dir, struct dir_context *ctx) 
 * output buffer.

 *

 * On return, @ctx->pos contains an offset that will read the next entry

 * in this directory when shmem_readdir() is called again with @ctx.

 * in this directory when offset_readdir() is called again with @ctx.

 *

 * Return values:

 *   %0 - Complete
@@ -479,7 +476,7 @@ static int offset_readdir(struct file *file, struct dir_context *ctx) 
	if (!dir_emit_dots(file, ctx))

		return 0;



	offset_iterate_dir(dir, ctx);

	offset_iterate_dir(d_inode(dir), ctx);

	return 0;

}