linux-kernel - Re: [Patch v2 02/15] CIFS: Add support for direct pages in rdata

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Date:   Sat, 23 Jun 2018 21:50:20 -0400
From:   Tom Talpey <tom@...pey.com>
To:     longli@...rosoft.com, Steve French <sfrench@...ba.org>,
        linux-cifs@...r.kernel.org, samba-technical@...ts.samba.org,
        linux-kernel@...r.kernel.org, linux-rdma@...r.kernel.org
Subject: Re: [Patch v2 02/15] CIFS: Add support for direct pages in rdata

On 5/30/2018 3:47 PM, Long Li wrote:
> From: Long Li <longli@...rosoft.com>
> 
> Add a function to allocate rdata without allocating pages for data
> transfer. This gives the caller an option to pass a number of pages
> that point to the data buffer.
> 
> rdata is still reponsible for free those pages after it's done.

"Caller" is still responsible? Or is the rdata somehow freeing itself
via another mechanism?

> 
> Signed-off-by: Long Li <longli@...rosoft.com>
> ---
>   fs/cifs/cifsglob.h |  2 +-
>   fs/cifs/file.c     | 23 ++++++++++++++++++++---
>   2 files changed, 21 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
> index 8d16c3e..56864a87 100644
> --- a/fs/cifs/cifsglob.h
> +++ b/fs/cifs/cifsglob.h
> @@ -1179,7 +1179,7 @@ struct cifs_readdata {
>   	unsigned int			tailsz;
>   	unsigned int			credits;
>   	unsigned int			nr_pages;
> -	struct page			*pages[];
> +	struct page			**pages;

Technically speaking, these are syntactically equivalent. It may not
be worth changing this historic definition.

Tom.


>   };
>   
>   struct cifs_writedata;
> diff --git a/fs/cifs/file.c b/fs/cifs/file.c
> index 23fd430..1c98293 100644
> --- a/fs/cifs/file.c
> +++ b/fs/cifs/file.c
> @@ -2880,13 +2880,13 @@ cifs_strict_writev(struct kiocb *iocb, struct iov_iter *from)
>   }
>   
>   static struct cifs_readdata *
> -cifs_readdata_alloc(unsigned int nr_pages, work_func_t complete)
> +cifs_readdata_direct_alloc(struct page **pages, work_func_t complete)
>   {
>   	struct cifs_readdata *rdata;
>   
> -	rdata = kzalloc(sizeof(*rdata) + (sizeof(struct page *) * nr_pages),
> -			GFP_KERNEL);
> +	rdata = kzalloc(sizeof(*rdata), GFP_KERNEL);
>   	if (rdata != NULL) {
> +		rdata->pages = pages;
>   		kref_init(&rdata->refcount);
>   		INIT_LIST_HEAD(&rdata->list);
>   		init_completion(&rdata->done);
> @@ -2896,6 +2896,22 @@ cifs_readdata_alloc(unsigned int nr_pages, work_func_t complete)
>   	return rdata;
>   }
>   
> +static struct cifs_readdata *
> +cifs_readdata_alloc(unsigned int nr_pages, work_func_t complete)
> +{
> +	struct page **pages =
> +		kzalloc(sizeof(struct page *) * nr_pages, GFP_KERNEL);
> +	struct cifs_readdata *ret = NULL;
> +
> +	if (pages) {
> +		ret = cifs_readdata_direct_alloc(pages, complete);
> +		if (!ret)
> +			kfree(pages);
> +	}
> +
> +	return ret;
> +}
> +
>   void
>   cifs_readdata_release(struct kref *refcount)
>   {
> @@ -2910,6 +2926,7 @@ cifs_readdata_release(struct kref *refcount)
>   	if (rdata->cfile)
>   		cifsFileInfo_put(rdata->cfile);
>   
> +	kvfree(rdata->pages);
>   	kfree(rdata);
>   }
>   
>