ceph: combine as many iovec as possile into one OSD request

Both ceph_sync_direct_write and ceph_sync_read iterate iovec elements
one by one, send one OSD request for each iovec. This is sub-optimal,
We can combine serveral iovec into one page vector, and send an OSD
request for the whole page vector.
Signed-off-by: Zhu, Caifeng <zhucaifeng@unissoft-nj.com>
Signed-off-by: Yan, Zheng <zyan@redhat.com>

fs/ceph/file.c

@@ -34,6 +34,74 @@
  * need to wait for MDS acknowledgement.
  */
 
+/*
+ * Calculate the length sum of direct io vectors that can
+ * be combined into one page vector.
+ */
+static size_t dio_get_pagev_size(const struct iov_iter *it)
+{
+    const struct iovec *iov = it->iov;
+    const struct iovec *iovend = iov + it->nr_segs;
+    size_t size;
+
+    size = iov->iov_len - it->iov_offset;
+    /*
+     * An iov can be page vectored when both the current tail
+     * and the next base are page aligned.
+     */
+    while (PAGE_ALIGNED((iov->iov_base + iov->iov_len)) &&
+           (++iov < iovend && PAGE_ALIGNED((iov->iov_base)))) {
+        size += iov->iov_len;
+    }
+    dout("dio_get_pagevlen len = %zu\n", size);
+    return size;
+}
+
+/*
+ * Allocate a page vector based on (@it, @nbytes).
+ * The return value is the tuple describing a page vector,
+ * that is (@pages, @page_align, @num_pages).
+ */
+static struct page **
+dio_get_pages_alloc(const struct iov_iter *it, size_t nbytes,
+		    size_t *page_align, int *num_pages)
+{
+	struct iov_iter tmp_it = *it;
+	size_t align;
+	struct page **pages;
+	int ret = 0, idx, npages;
+
+	align = (unsigned long)(it->iov->iov_base + it->iov_offset) &
+		(PAGE_SIZE - 1);
+	npages = calc_pages_for(align, nbytes);
+	pages = kmalloc(sizeof(*pages) * npages, GFP_KERNEL);
+	if (!pages) {
+		pages = vmalloc(sizeof(*pages) * npages);
+		if (!pages)
+			return ERR_PTR(-ENOMEM);
+	}
+
+	for (idx = 0; idx < npages; ) {
+		size_t start;
+		ret = iov_iter_get_pages(&tmp_it, pages + idx, nbytes,
+					 npages - idx, &start);
+		if (ret < 0)
+			goto fail;
+
+		iov_iter_advance(&tmp_it, ret);
+		nbytes -= ret;
+		idx += (ret + start + PAGE_SIZE - 1) / PAGE_SIZE;
+	}
+
+	BUG_ON(nbytes != 0);
+	*num_pages = npages;
+	*page_align = align;
+	dout("dio_get_pages_alloc: got %d pages align %zu\n", npages, align);
+	return pages;
+fail:
+	ceph_put_page_vector(pages, idx, false);
+	return ERR_PTR(ret);
+}
 
 /*
  * Prepare an open request.  Preallocate ceph_cap to avoid an
@@ -458,11 +526,10 @@ static ssize_t ceph_sync_read(struct kiocb *iocb, struct iov_iter *i,
 			size_t start;
 			ssize_t n;
 
-			n = iov_iter_get_pages_alloc(i, &pages, INT_MAX, &start);
-			if (n < 0)
-				return n;
-
-			num_pages = (n + start + PAGE_SIZE - 1) / PAGE_SIZE;
+			n = dio_get_pagev_size(i);
+			pages = dio_get_pages_alloc(i, n, &start, &num_pages);
+			if (IS_ERR(pages))
+				return PTR_ERR(pages);
 
 			ret = striped_read(inode, off, n,
 					   pages, num_pages, checkeof,
@@ -592,7 +659,7 @@ ceph_sync_direct_write(struct kiocb *iocb, struct iov_iter *from, loff_t pos,
 		CEPH_OSD_FLAG_WRITE;
 
 	while (iov_iter_count(from) > 0) {
-		u64 len = iov_iter_single_seg_count(from);
+		u64 len = dio_get_pagev_size(from);
 		size_t start;
 		ssize_t n;
 
@@ -611,14 +678,14 @@ ceph_sync_direct_write(struct kiocb *iocb, struct iov_iter *from, loff_t pos,
 
 		osd_req_op_init(req, 1, CEPH_OSD_OP_STARTSYNC, 0);
 
-		n = iov_iter_get_pages_alloc(from, &pages, len, &start);
-		if (unlikely(n < 0)) {
-			ret = n;
+		n = len;
+		pages = dio_get_pages_alloc(from, len, &start, &num_pages);
+		if (IS_ERR(pages)) {
 			ceph_osdc_put_request(req);
+			ret = PTR_ERR(pages);
 			break;
 		}
 
-		num_pages = (n + start + PAGE_SIZE - 1) / PAGE_SIZE;
 		/*
 		 * throw out any page cache pages in this range. this
 		 * may block.