[Devel] [PATCH 11/11] fuse: optimize __fuse_direct_io()

[Maxim Patlasov]

__fuse_direct_io() allocates fuse-requests by calling fuse_get_req(fc, n). The
patch calculates 'n' based on iov[] array. This is useful because allocating
FUSE_MAX_PAGES_PER_REQ page pointers and descriptors for each fuse request
would be waste of memory in case of iov-s of smaller size.

Signed-off-by: Maxim Patlasov <mpatlasov at parallels.com>
---
 fs/fuse/file.c |   27 +++++++++++++++++++++++----
 1 files changed, 23 insertions(+), 4 deletions(-)

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 5b0fa5d..5ecab19 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -1090,14 +1090,14 @@ static int fuse_get_user_pages(struct fuse_req *req,
 		return 0;
 	}
 
-	while (nbytes < *nbytesp && req->num_pages < FUSE_MAX_PAGES_PER_REQ) {
+	while (nbytes < *nbytesp && req->num_pages < req->max_pages) {
 		int npages;
 		unsigned long user_addr = fuse_get_ua(*iov_pp, *iov_offset_p);
 		unsigned offset = user_addr & ~PAGE_MASK;
 		size_t frag_size = fuse_get_fr_sz(*iov_pp, *iov_offset_p,
 						  *nbytesp - nbytes);
 
-		int n = FUSE_MAX_PAGES_PER_REQ - req->num_pages;
+		int n = req->max_pages - req->num_pages;
 		frag_size = min_t(size_t, frag_size, n << PAGE_SHIFT);
 
 		npages = (frag_size + offset + PAGE_SIZE - 1) >> PAGE_SHIFT;
@@ -1138,6 +1138,24 @@ static int fuse_get_user_pages(struct fuse_req *req,
 	return 0;
 }
 
+static inline int fuse_iov_npages(const struct iovec *iov,
+				  unsigned long nr_segs, size_t iov_offset)
+{
+	int npages = 0;
+
+	while (nr_segs-- > 0 && npages < FUSE_MAX_PAGES_PER_REQ) {
+		unsigned long user_addr = fuse_get_ua(iov, iov_offset);
+		unsigned offset = user_addr & ~PAGE_MASK;
+		size_t frag_size = iov->iov_len - iov_offset;
+
+		npages += (frag_size + offset + PAGE_SIZE - 1) >> PAGE_SHIFT;
+		iov++;
+		iov_offset = 0;
+	}
+
+	return min(npages, FUSE_MAX_PAGES_PER_REQ);
+}
+
 static ssize_t __fuse_direct_io(struct file *file, const struct iovec *iov,
 				unsigned long nr_segs, size_t count,
 				loff_t *ppos, int write)
@@ -1150,7 +1168,7 @@ static ssize_t __fuse_direct_io(struct file *file, const struct iovec *iov,
 	struct fuse_req *req;
 	size_t iov_offset = 0;
 
-	req = fuse_get_req(fc, FUSE_MAX_PAGES_PER_REQ);
+	req = fuse_get_req(fc, fuse_iov_npages(iov, nr_segs, iov_offset));
 	if (IS_ERR(req))
 		return PTR_ERR(req);
 
@@ -1186,7 +1204,8 @@ static ssize_t __fuse_direct_io(struct file *file, const struct iovec *iov,
 			break;
 		if (count) {
 			fuse_put_request(fc, req);
-			req = fuse_get_req(fc, FUSE_MAX_PAGES_PER_REQ);
+			req = fuse_get_req(fc,
+				fuse_iov_npages(iov, nr_segs, iov_offset));
 			if (IS_ERR(req))
 				break;
 		}