[Devel] Re: [PATCH 1/6] fuse: general infrastructure for pages[] of variable size

[Miklos Szeredi]

Maxim Patlasov <mpatlasov at parallels.com> writes:

> The patch removes inline array of FUSE_MAX_PAGES_PER_REQ page pointers from
> fuse_req. Instead of that, req->pages may now point either to small inline
> array or to an array allocated dynamically.
>
> This essentially means that all callers of fuse_request_alloc[_nofs] should
> pass the number of pages needed explicitly.
>
> The patch doesn't make any logic changes.

See comments inline.


> ---
>  fs/fuse/dev.c    |   40 ++++++++++++++++++++++++++++++----------
>  fs/fuse/file.c   |    4 ++--
>  fs/fuse/fuse_i.h |    9 ++++++---
>  fs/fuse/inode.c  |    4 ++--
>  4 files changed, 40 insertions(+), 17 deletions(-)
>
> diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
> index 7df2b5e..c0283a1 100644
> --- a/fs/fuse/dev.c
> +++ b/fs/fuse/dev.c
> @@ -36,32 +36,52 @@ static struct fuse_conn *fuse_get_conn(struct file *file)
>  
>  static void fuse_request_init(struct fuse_req *req)
>  {
> +	struct page **pages = req->pages;
> +

Rather than this, make fuse_request_init() take 'pages' as a second
argument.

>  	memset(req, 0, sizeof(*req));
>  	INIT_LIST_HEAD(&req->list);
>  	INIT_LIST_HEAD(&req->intr_entry);
>  	init_waitqueue_head(&req->waitq);
>  	atomic_set(&req->count, 1);
> +
> +	req->pages = pages;
>  }
>  
> -struct fuse_req *fuse_request_alloc(void)
> +static struct fuse_req *__fuse_request_alloc(int npages, gfp_t flags)
>  {
> -	struct fuse_req *req = kmem_cache_alloc(fuse_req_cachep, GFP_KERNEL);
> -	if (req)
> +	struct fuse_req *req = kmem_cache_alloc(fuse_req_cachep, flags);
> +	if (req) {
> +		if (npages <= 1)

Instead of '1' use a constant (e.g. FUSE_REQ_INLINE_PAGES)

> +			req->pages = req->inline_pages;
> +		else
> +			req->pages = kmalloc(sizeof(struct page *) * npages,
> +					     flags);
> +
> +		if (!req->pages) {
> +			kmem_cache_free(fuse_req_cachep, req);
> +			return NULL;
> +		}
> +
>  		fuse_request_init(req);
> +	}
>  	return req;
>  }
> +
> +struct fuse_req *fuse_request_alloc(int npages)
> +{
> +	return __fuse_request_alloc(npages, GFP_KERNEL);
> +}
>  EXPORT_SYMBOL_GPL(fuse_request_alloc);
>  
> -struct fuse_req *fuse_request_alloc_nofs(void)
> +struct fuse_req *fuse_request_alloc_nofs(int npages)
>  {
> -	struct fuse_req *req = kmem_cache_alloc(fuse_req_cachep, GFP_NOFS);
> -	if (req)
> -		fuse_request_init(req);
> -	return req;
> +	return __fuse_request_alloc(npages, GFP_NOFS);
>  }
>  
>  void fuse_request_free(struct fuse_req *req)
>  {
> +	if (req->pages != req->inline_pages)
> +		kfree(req->pages);
>  	kmem_cache_free(fuse_req_cachep, req);
>  }
>  
> @@ -116,7 +136,7 @@ struct fuse_req *fuse_get_req(struct fuse_conn *fc)
>  	if (!fc->connected)
>  		goto out;
>  
> -	req = fuse_request_alloc();
> +	req = fuse_request_alloc(FUSE_MAX_PAGES_PER_REQ);
>  	err = -ENOMEM;
>  	if (!req)
>  		goto out;
> @@ -193,7 +213,7 @@ struct fuse_req *fuse_get_req_nofail(struct fuse_conn *fc, struct file *file)
>  
>  	atomic_inc(&fc->num_waiting);
>  	wait_event(fc->blocked_waitq, !fc->blocked);
> -	req = fuse_request_alloc();
> +	req = fuse_request_alloc(FUSE_MAX_PAGES_PER_REQ);
>  	if (!req)
>  		req = get_reserved_req(fc, file);
>  
> diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> index aba15f1..7423ea4 100644
> --- a/fs/fuse/file.c
> +++ b/fs/fuse/file.c
> @@ -57,7 +57,7 @@ struct fuse_file *fuse_file_alloc(struct fuse_conn *fc)
>  		return NULL;
>  
>  	ff->fc = fc;
> -	ff->reserved_req = fuse_request_alloc();
> +	ff->reserved_req = fuse_request_alloc(0);
>  	if (unlikely(!ff->reserved_req)) {
>  		kfree(ff);
>  		return NULL;
> @@ -1272,7 +1272,7 @@ static int fuse_writepage_locked(struct page *page)
>  
>  	set_page_writeback(page);
>  
> -	req = fuse_request_alloc_nofs();
> +	req = fuse_request_alloc_nofs(1);
>  	if (!req)
>  		goto err;
>  
> diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
> index e24dd74..5e78840 100644
> --- a/fs/fuse/fuse_i.h
> +++ b/fs/fuse/fuse_i.h
> @@ -291,7 +291,10 @@ struct fuse_req {
>  	} misc;
>  
>  	/** page vector */
> -	struct page *pages[FUSE_MAX_PAGES_PER_REQ];
> +	struct page **pages;
> +
> +	/** inline page vector */
> +	struct page *inline_pages[1];
>  

To defend against programming errors, I think it would be wise to add

	/** size of the 'pages' array */
	unsigned max_pages;

so that when storing pages in the array we can check whether we are
overflowing the array.

>  	/** number of pages in vector */
>  	unsigned num_pages;
> @@ -658,9 +661,9 @@ void fuse_ctl_cleanup(void);
>  /**
>   * Allocate a request
>   */
> -struct fuse_req *fuse_request_alloc(void);
> +struct fuse_req *fuse_request_alloc(int npages);
>  
> -struct fuse_req *fuse_request_alloc_nofs(void);
> +struct fuse_req *fuse_request_alloc_nofs(int npages);
>  
>  /**
>   * Free a request
> diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
> index ce0a283..3f399ba 100644
> --- a/fs/fuse/inode.c
> +++ b/fs/fuse/inode.c
> @@ -1027,12 +1027,12 @@ static int fuse_fill_super(struct super_block *sb, void *data, int silent)
>  	/* only now - we want root dentry with NULL ->d_op */
>  	sb->s_d_op = &fuse_dentry_operations;
>  
> -	init_req = fuse_request_alloc();
> +	init_req = fuse_request_alloc(0);
>  	if (!init_req)
>  		goto err_put_root;
>  
>  	if (is_bdev) {
> -		fc->destroy_req = fuse_request_alloc();
> +		fc->destroy_req = fuse_request_alloc(0);
>  		if (!fc->destroy_req)
>  			goto err_free_init_req;
>  	}