zfs very poor performance compared to ufs due to lack of cache?

[Andriy Gapon]

on 07/09/2010 10:26 Andriy Gapon said the following:
> Interesting.  I briefly looked at the code in mappedread(), zfs_vnops.c, and I
> have a VM question.
> Shouldn't we mark the corresponding page bits as valid after reading data into
> the page?
> I specifically speak of the block that starts with the following line:
> } else if (m != NULL && uio->uio_segflg == UIO_NOCOPY) {
> I am taking mdstart_swap as an example and it does m->valid = VM_PAGE_BITS_ALL.
> 

I've chatted with and conclusion seems to be that vm_page_set_validclean() call
should be added at the end of the block.

Perhaps, something like this:

--- a/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_vnops.c
+++ b/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_vnops.c
@@ -500,6 +500,7 @@ again:
 				sched_unpin();
 			}
 			VM_OBJECT_LOCK(obj);
+			vm_page_set_validclean(m, off, bytes);
 			vm_page_wakeup(m);
 			if (error == 0)
 				uio->uio_resid -= bytes;


BTW, I think that 'off' variable can be made of 'int' type, as it is an offset
within a page; no need for int64.

-- 
Andriy Gapon