iscsi: use pageslab

[email protected]:

We cannot handle filesystems like XFS becuase of the pages they are sending us. We had thought page_count could be used to work around this, but the correct test is for PageSlab.

The proper solution is to figure out what type of pages filesystems can use so we do not have to add tests like this or handle it in the block layer for all network block drivers but the issue still has not been resolved on fs-devel so we are sending this patch as a temporary fix.

This is last patch just in case it is Nakd with the explanation that we need to push the correct fix through fs-devel, mm or the block layer. The rest of the patchset can live without the patch, but the driver will not work with filesystems like XFS.

index b17c121..8146cf9 100644
@@ -109,7 +109,7 @@ iscsi_buf_init_sg(struct iscsi_buf *ibuf
 	/*
 	 * Fastpath: sg element fits into single page
 	 */
-	if (sg->length + sg->offset <= PAGE_SIZE && page_count(sg->page) >= 2)
+	if (sg->length + sg->offset <= PAGE_SIZE && !PageSlab(sg->page))
 		ibuf->use_sendmsg = 0;
 	else
 		ibuf->use_sendmsg = 1;