[lkml]   [2008]   [Jan]   [16]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [PATCH] mmu notifiers #v2
Andrea Arcangeli wrote:
> This patch is last version of a basic implementation of the mmu
> notifiers.
> In short when the linux VM decides to free a page, it will unmap it
> from the linux pagetables. However when a page is mapped not just by
> the regular linux ptes, but also from the shadow pagetables, it's
> currently unfreeable by the linux VM.
> This patch allows the shadow pagetables to be dropped and the page to
> be freed after that, if the linux VM decides to unmap the page from
> the main ptes because it wants to swap out the page.
> [...]
> Comments welcome... especially from SGI/IBM/Quadrics and all other
> potential users of this functionality.

For HPC, this should be very interesting. Managing the registration
cache of high-speed networks from user-space is a huge mess. This
approach should help a lot. In fact, back in 2004, I implemented
something similar called vmaspy to update the regcache of Myrinet
drivers. I never submitted any patch because Infiniband would have been
the only user in the mainline kernel and they were reluctant to these
ideas [1]. In the meantime, some of them apparently changed their mind
since they implemented some vmops-overriding hack to do something
similar [2]. This patch should simplify all this.

One of the difference with my patch is that you attach the notifier list
to the mm_struct while my code attached it to vmas. But I now don't
think it was such a good idea since it probably didn't reduce the number
of notifier calls a lot.

Also, one thing that I looked at in vmaspy was notifying fork. I am not
sure what happens on Copy-on-write with your code, but for sure C-o-w is
problematic for shadow page tables. I thought shadow pages should just
be invalidated when a fork happens and the caller would refill them
after forcing C-o-w or so. So adding a notifier call there too might be



 \ /
  Last update: 2008-01-16 10:03    [W:0.183 / U:3.136 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site