On Thu, Sep 27, 2018 at 3:52 PM, Dan Schatzberg <dschatzberg@xxxxxx> wrote:
> FUSE file reads are cached in the page cache, but symlink reads are
> not. This patch enables FUSE READLINK operations to be cached which
> can improve performance of some FUSE workloads.
>
> In particular, I'm working on a FUSE filesystem for access to source
> code and discovered that about a 10% improvement to build times is
> achieved with this patch (there are a lot of symlinks in the source
> tree).
>
> Please provide feedback, I'm looking to flesh this out more.
Need to think about how/when to invalidate the cached symlink
contents. I think treating it like metadata (i.e. look at
attr_timeout for validity) would be the simplest.
Thanks,
Miklos
>
> Signed-off-by: Dan Schatzberg <dschatzberg@xxxxxx>
> ---
> fs/fuse/dir.c | 70 +++++++++++++++++++++++++++++++--------------------
> 1 file changed, 43 insertions(+), 27 deletions(-)
>
> diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
> index 0979609d6eba..3c0a81ef5bca 100644
> --- a/fs/fuse/dir.c
> +++ b/fs/fuse/dir.c
> @@ -1398,38 +1398,46 @@ static int fuse_readdir(struct file *file, struct dir_context *ctx)
> return err;
> }
>
> -static const char *fuse_get_link(struct dentry *dentry,
> - struct inode *inode,
> - struct delayed_call *done)
> +static int fuse_symlink_readpage(struct file *file, struct page *page)
> {
> + struct inode *inode = page->mapping->host;
> struct fuse_conn *fc = get_fuse_conn(inode);
> - FUSE_ARGS(args);
> - char *link;
> - ssize_t ret;
> -
> - if (!dentry)
> - return ERR_PTR(-ECHILD);
> + struct fuse_req *req;
> + int err;
> + size_t num_read;
>
> - link = kmalloc(PAGE_SIZE, GFP_KERNEL);
> - if (!link)
> - return ERR_PTR(-ENOMEM);
> + err = -EIO;
> + if (is_bad_inode(inode))
> + goto out;
>
> - args.in.h.opcode = FUSE_READLINK;
> - args.in.h.nodeid = get_node_id(inode);
> - args.out.argvar = 1;
> - args.out.numargs = 1;
> - args.out.args[0].size = PAGE_SIZE - 1;
> - args.out.args[0].value = link;
> - ret = fuse_simple_request(fc, &args);
> - if (ret < 0) {
> - kfree(link);
> - link = ERR_PTR(ret);
> - } else {
> - link[ret] = '\0';
> - set_delayed_call(done, kfree_link, link);
> + req = fuse_get_req(fc, 1);
> + if (IS_ERR(req)) {
> + err = PTR_ERR(req);
> + goto out;
> }
> +
> + req->out.page_zeroing = 1;
> + req->out.argpages = 1;
> + req->num_pages = 1;
> + req->pages[0] = page;
> + req->page_descs[0].length = PAGE_SIZE - 1;
> + req->in.h.opcode = FUSE_READLINK;
> + req->in.h.nodeid = get_node_id(inode);
> + req->out.argvar = 1;
> + req->out.numargs = 1;
> + req->out.args[0].size = PAGE_SIZE - 1;
> + fuse_request_send(fc, req);
> + num_read = req->out.args[0].size;
> + err = req->out.h.error;
> +
> + if (!err)
> + SetPageUptodate(page);
> +
> + fuse_put_request(fc, req);
> fuse_invalidate_atime(inode);
> - return link;
> +out:
> + unlock_page(page);
> + return err;
> }
>
> static int fuse_dir_open(struct inode *inode, struct file *file)
> @@ -1855,7 +1863,7 @@ static const struct inode_operations fuse_common_inode_operations = {
>
> static const struct inode_operations fuse_symlink_inode_operations = {
> .setattr = fuse_setattr,
> - .get_link = fuse_get_link,
> + .get_link = page_get_link,
> .getattr = fuse_getattr,
> .listxattr = fuse_listxattr,
> };
> @@ -1871,7 +1879,15 @@ void fuse_init_dir(struct inode *inode)
> inode->i_fop = &fuse_dir_operations;
> }
>
> +static const struct address_space_operations fuse_symlink_aops = {
> + .readpage = fuse_symlink_readpage,
> +};
> +
> void fuse_init_symlink(struct inode *inode)
> {
> inode->i_op = &fuse_symlink_inode_operations;
> + inode->i_data.a_ops = &fuse_symlink_aops;
> + mapping_set_gfp_mask(inode->i_mapping,
> + mapping_gfp_constraint(inode->i_mapping,
> + ~(__GFP_FS | __GFP_HIGHMEM)));
> }
> --
> 2.17.1
>
