svn commit: r248185 - user/attilio/vmcontention/sys/vm

[Alan Cox]

On 03/12/2013 07:04, Attilio Rao wrote:
> On Tue, Mar 12, 2013 at 7:14 AM, Alan Cox <alc at freebsd.org> wrote:
>> Author: alc
>> Date: Tue Mar 12 06:14:31 2013
>> New Revision: 248185
>> URL: http://svnweb.freebsd.org/changeset/base/248185
>>
>> Log:
>>   When transferring the page from one object to another, don't insert the
>>   page into its new object until the page's pindex has been updated.
>>   Otherwise, one code path within vm_radix_insert() may use the wrong
>>   pindex value.
> This is just a style change really because the code already subtracts
> offindxstart from current m->pindex when inserting. The pindex on the
> page is then adjusted when the real subtraction happens.
> IIRC, I did this way because of less diffs against -CURRENT, but the
> code looks correct to me already in the older version.
>

No, as I say in the commit message, there is a path in vm_radix_insert()
that uses "page->pindex" and not the "index" argument:

        /*
         * A new node is needed because the right insertion level is
reached.
         * Setup the new intermediate node and add the 2 children: the
         * new object and the older edge.
         */
        tmp2 = vm_radix_node_get(vm_radix_trimkey(page->pindex, clev -
1), 2,
            clev);

Prior to this change, if we follow this path, then we are using the
wrong "pindex" value at this point in vm_radix_insert().