trying mmap-ed first for large ranges

src/block/bio.c

@@ -842,6 +842,8 @@ EXPORT_SYMBOL(bio_add_page);
  * For multi-segment *iter, this function only adds pages from the
  * the next non-empty segment of the iov iterator.
  */
+// undefine to skip
+#define SUSPECT_MMAPED (4 * PAGE_SIZE)
 static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
 {
 	unsigned short nr_pages = bio->bi_max_vecs - bio->bi_vcnt, idx;
@@ -854,12 +856,25 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
 		pr_debug(" *B* niter->type=%d, iter->iov_offset=0x%08x, iter->count=0x%08x, iter->nr_segs=0x%08lx",\
 				iter->type, iter->iov_offset,iter->count,iter->nr_segs); // *B* niter->type=1, iter->iov_offset=0x00000000, iter->count=0x0009f000, iter->nr_segs=0x00000001
 	}
-
+// If suspected "Elphel" - try it first?
+#ifdef SUSPECT_MMAPED
+	if (( bio->bi_vcnt == 0) && (iter->iov_offset == 0) && (iter->nr_segs == 1) && (iter->count >= SUSPECT_MMAPED)) {
+		pr_debug(" *B1* Suspecting mmaped memory, iter->count=0x%08x > 0x%08x", iter->count, (int) SUSPECT_MMAPED);
+		size= iov_iter_get_pages_elphel(iter, pages, LONG_MAX, nr_pages, &offset);  // try mmap-ed
+		if (size < 0){
+			pr_debug("mmaped failed (err=%d) trying pinning userspace memory", size);
+			size = iov_iter_get_pages(iter, pages, LONG_MAX, nr_pages, &offset);  // regular way with userspace
+		}
+	} else {
+		size = iov_iter_get_pages(iter, pages, LONG_MAX, nr_pages, &offset); // regular way with userspace
+	}
+#else
 	size = iov_iter_get_pages(iter, pages, LONG_MAX, nr_pages, &offset);
+#endif
 	if (unlikely(size <= 0)) {
 		pr_debug("Error=%d, trying continuous mmap-ed pages, bio->bi_vcnt=0x%04x,  bio->bi_max_vecs=0x%04x, offset=0x%08x",
 				size, bio->bi_vcnt,  bio->bi_max_vecs, offset);
-		if ((size == -EFAULT) && ( bio->bi_vcnt == 0) && (offset == 0) && (iter->nr_segs == 1)){ // Only for all pages, single segment
+		if ((size == -EFAULT) && ( bio->bi_vcnt == 0) && (iter->iov_offset == 0) && (iter->nr_segs == 1)){ // Only for all pages, single segment
 			size= iov_iter_get_pages_elphel(iter, pages, LONG_MAX, nr_pages, &offset);
 		}
 		if (unlikely(size <= 0)) {