[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [PATCH v3 05/19] xen/arm: mm: Add support for the contiguous bit



Hi,

On 02/04/2022 00:53, Stefano Stabellini wrote:
On Mon, 21 Feb 2022, Julien Grall wrote:
@@ -1333,21 +1386,34 @@ static int xen_pt_update(unsigned long virt,
      while ( left )
      {
          unsigned int order, level;
+        unsigned int nr_contig;
+        unsigned int new_flags;
level = xen_pt_mapping_level(vfn, mfn, left, flags);
          order = XEN_PT_LEVEL_ORDER(level);
ASSERT(left >= BIT(order, UL)); - rc = xen_pt_update_entry(root, pfn_to_paddr(vfn), mfn, level, flags);
-        if ( rc )
-            break;
+        /*
+         * Check if we can set the contiguous mapping and update the
+         * flags accordingly.
+         */
+        nr_contig = xen_pt_check_contig(vfn, mfn, level, left, flags);
+        new_flags = flags | ((nr_contig > 1) ? _PAGE_CONTIG : 0);

Here is an optional idea to make the code simpler. We could move the
flags changes (adding/removing _PAGE_CONTIG) to xen_pt_check_contig.
That way, we could remove the inner loop.

xen_pt_check_contig could check if _PAGE_CONTIG is already set and based
on alignment, it should be able to figure out when it needs to be
disabled.

My initial attempt was to do everything in a loop. But this didn't pan out as I wanted (I felt the code was complex) and there are extra work to be done for the next 31 entries (assuming 4KB granularity).

Hence the two loops. Unfortunately, I didn't keep my first attempt. So I can't realy show what I wrote.

Cheers,

--
Julien Grall



 


Rackspace

Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.