Re: [PATCH v3 5/5] nfs: introduce nfs_direct_extract_pages helper

[Trond Myklebust <trondmy@kernel.org>]

On Wed, 2026-07-15 at 14:35 +0000, Pranjal Shrivastava wrote:
> Introduce nfs_direct_extract_pages() in direct.c to centralize page
> extraction and request creation for the Direct I/O path. The helper
> manages extraction from the iters and builds a list of nfs_page
> requests
> 
> Refactor nfs_direct_read_schedule_iovec() and
> nfs_direct_write_schedule_iovec() to utilize the new helper, unifying
> the extraction logic on both paths.
> 
> Signed-off-by: Pranjal Shrivastava <praan@google.com>
> ---
>  fs/nfs/direct.c | 127 ++++++++++++++++++++++++----------------------
> --
>  1 file changed, 64 insertions(+), 63 deletions(-)
> 
> diff --git a/fs/nfs/direct.c b/fs/nfs/direct.c
> index b9ac0a67693c..d31e4720ffff 100644
> --- a/fs/nfs/direct.c
> +++ b/fs/nfs/direct.c
> @@ -178,6 +178,50 @@ static void nfs_direct_release_pages(struct page
> **pages, unsigned int npages,
>  	}
>  }
>  
> +static ssize_t nfs_direct_extract_pages(struct nfs_direct_req *dreq,
> +					 struct iov_iter *iter,
> +					 size_t size, loff_t *pos,
> +					 struct list_head *list)
> +{
> +	bool pinned = iov_iter_extract_will_pin(iter);
> +	struct page **pagevec = NULL;
> +	ssize_t result, bytes = 0;
> +	unsigned int npages, i;
> +	size_t pgbase;
> +
> +	result = iov_iter_extract_pages(iter, &pagevec, size, ~0U,
> 0, &pgbase);
> +	if (result <= 0)
> +		return result;
> +
> +	npages = (result + pgbase + PAGE_SIZE - 1) >> PAGE_SHIFT;
> +	for (i = 0; i < npages; i++) {
> +		struct nfs_page *req;
> +		unsigned int req_len = min_t(size_t, result - bytes,
> PAGE_SIZE - pgbase);
> +
> +		req = nfs_page_create_from_page(dreq->ctx,
> pagevec[i],
> +						pinned, pgbase,
> *pos,
> +						req_len);
> +		if (IS_ERR(req)) {
> +			if (!bytes)
> +				bytes = PTR_ERR(req);
> +			break;
> +		}
> +
> +		list_add_tail(&req->wb_list, list);
> +		pgbase = 0;
> +		bytes += req_len;
> +		*pos += req_len;
> +	}
> +
> +	if (i < npages) {
> +		iov_iter_revert(iter, result - bytes);

Oopsable if bytes == PTR_ERR(req)

> +		nfs_direct_release_pages(pagevec + i, npages - i,
> pinned);

See what happens above with swap over NFS (which sets pinned = false).

> +	}
> +
> +	kvfree(pagevec);
> +	return bytes;
> +}
> +
>  void nfs_init_cinfo_from_dreq(struct nfs_commit_info *cinfo,
>  			      struct nfs_direct_req *dreq)
>  {
> @@ -346,6 +390,7 @@ static ssize_t
> nfs_direct_read_schedule_iovec(struct nfs_direct_req *dreq,
>  	ssize_t result = -EINVAL;
>  	size_t requested_bytes = 0;
>  	size_t rsize = max_t(size_t, NFS_SERVER(inode)->rsize,
> PAGE_SIZE);
> +	LIST_HEAD(nfs_page_list);
>  
>  	nfs_pageio_init_read(&desc, dreq->inode, false,
>  			     &nfs_direct_read_completion_ops);
> @@ -354,43 +399,23 @@ static ssize_t
> nfs_direct_read_schedule_iovec(struct nfs_direct_req *dreq,
>  	inode_dio_begin(inode);
>  
>  	while (iov_iter_count(iter)) {
> -		struct page **pagevec = NULL;
> -		size_t bytes;
> -		size_t pgbase;
> -		unsigned npages, i;
> -		bool pinned = iov_iter_extract_will_pin(iter);
> -
> -		result = iov_iter_extract_pages(iter, &pagevec,
> -						rsize, ~0U, 0,
> &pgbase);
> +		result = nfs_direct_extract_pages(dreq, iter, rsize,
> &pos, &nfs_page_list);
>  		if (result < 0)
>  			break;
>  
> -		bytes = result;
> -		npages = (result + pgbase + PAGE_SIZE - 1) /
> PAGE_SIZE;
> -		for (i = 0; i < npages; i++) {
> -			struct nfs_page *req;
> -			unsigned int req_len = min_t(size_t, bytes,
> PAGE_SIZE - pgbase);
> -			/* XXX do we need to do the eof zeroing
> found in async_filler? */
> -			req = nfs_page_create_from_page(dreq->ctx,
> pagevec[i],
> -							pinned,
> pgbase, pos,
> -							req_len);
> -			if (IS_ERR(req)) {
> -				result = PTR_ERR(req);
> -				break;
> -			}
> +		while (!list_empty(&nfs_page_list)) {
> +			struct nfs_page *req =
> nfs_list_entry(nfs_page_list.next);
> +			size_t req_len = req->wb_bytes;
> +
> +			nfs_list_remove_request(req);
>  			if (!nfs_pageio_add_request(&desc, req)) {
>  				result = desc.pg_error;
>  				nfs_release_request(req);
> +				nfs_release_request_list(&nfs_page_l
> ist);
>  				break;
>  			}
> -			pgbase = 0;
> -			bytes -= req_len;
>  			requested_bytes += req_len;
> -			pos += req_len;
>  		}
> -		if (i < npages)
> -			nfs_direct_release_pages(pagevec + i, npages
> - i, pinned);
> -		kvfree(pagevec);
>  		if (result < 0)
>  			break;
>  	}
> @@ -881,6 +906,7 @@ static ssize_t
> nfs_direct_write_schedule_iovec(struct nfs_direct_req *dreq,
>  	ssize_t result = 0;
>  	size_t requested_bytes = 0;
>  	size_t wsize = max_t(size_t, NFS_SERVER(inode)->wsize,
> PAGE_SIZE);
> +	LIST_HEAD(nfs_page_list);
>  	bool defer = false;
>  
>  	trace_nfs_direct_write_schedule_iovec(dreq);
> @@ -893,55 +919,32 @@ static ssize_t
> nfs_direct_write_schedule_iovec(struct nfs_direct_req *dreq,
>  
>  	NFS_I(inode)->write_io += iov_iter_count(iter);
>  	while (iov_iter_count(iter)) {
> -		struct page **pagevec = NULL;
> -		size_t bytes;
> -		size_t pgbase;
> -		unsigned npages, i;
> -		bool pinned = iov_iter_extract_will_pin(iter);
> -
> -		result = iov_iter_extract_pages(iter, &pagevec,
> -						wsize, ~0U, 0,
> &pgbase);
> +		result = nfs_direct_extract_pages(dreq, iter, wsize,
> &pos, &nfs_page_list);
>  		if (result < 0)
>  			break;
>  
> -		bytes = result;
> -		npages = (result + pgbase + PAGE_SIZE - 1) /
> PAGE_SIZE;
> -		for (i = 0; i < npages; i++) {
> -			struct nfs_page *req;
> -			unsigned int req_len = min_t(size_t, bytes,
> PAGE_SIZE - pgbase);
> -
> -			req = nfs_page_create_from_page(dreq->ctx,
> pagevec[i],
> -							pinned,
> pgbase, pos,
> -							req_len);
> -			if (IS_ERR(req)) {
> -				result = PTR_ERR(req);
> -				break;
> -			}
> -
> -			if (desc.pg_error < 0) {
> -				nfs_free_request(req);
> -				result = desc.pg_error;
> -				break;
> -			}
> -
> -			pgbase = 0;
> -			bytes -= req_len;
> -			requested_bytes += req_len;
> -			pos += req_len;
> +		while (!list_empty(&nfs_page_list)) {
> +			struct nfs_page *req =
> nfs_list_entry(nfs_page_list.next);
> +			size_t req_len = req->wb_bytes;
>  
> +			nfs_list_remove_request(req);
>  			if (defer) {
>  				nfs_mark_request_commit(req, NULL,
> &cinfo, 0);
> +				requested_bytes += req_len;
>  				continue;
>  			}
>  
>  			nfs_lock_request(req);
> -			if (nfs_pageio_add_request(&desc, req))
> +			if (nfs_pageio_add_request(&desc, req)) {
> +				requested_bytes += req_len;
>  				continue;
> +			}
>  
>  			/* Exit on hard errors */
>  			if (desc.pg_error < 0 && desc.pg_error != -
> EAGAIN) {
>  				result = desc.pg_error;
>  				nfs_unlock_and_release_request(req);
> +				nfs_release_request_list(&nfs_page_l
> ist);
>  				break;
>  			}
>  
> @@ -952,12 +955,10 @@ static ssize_t
> nfs_direct_write_schedule_iovec(struct nfs_direct_req *dreq,
>  			spin_unlock(&dreq->lock);
>  			nfs_unlock_request(req);
>  			nfs_mark_request_commit(req, NULL, &cinfo,
> 0);
> +			requested_bytes += req_len;
>  			desc.pg_error = 0;
>  			defer = true;
>  		}
> -		if (i < npages)
> -			nfs_direct_release_pages(pagevec + i, npages
> - i, pinned);
> -		kvfree(pagevec);
>  		if (result < 0)
>  			break;
>  	}

-- 
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trondmy@kernel.org, trond.myklebust@hammerspace.com