Messages in this thread | | | Subject | Re: [RFC v4][PATCH 4/9] Memory management (dump) | From | Dave Hansen <> | Date | Wed, 10 Sep 2008 09:55:28 -0700 |
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On Tue, 2008-09-09 at 03:42 -0400, Oren Laadan wrote: > + while (addr < end) { > + struct page *page; > + > + /* > + * simplified version of get_user_pages(): already have vma, > + * only need FOLL_TOUCH, and (for now) ignore fault stats. > + * > + * FIXME: consolidate with get_user_pages() > + */ > + > + cond_resched(); > + while (!(page = follow_page(vma, addr, FOLL_TOUCH))) { > + ret = handle_mm_fault(vma->vm_mm, vma, addr, 0); > + if (ret & VM_FAULT_ERROR) { > + if (ret & VM_FAULT_OOM) > + ret = -ENOMEM; > + else if (ret & VM_FAULT_SIGBUS) > + ret = -EFAULT; > + else > + BUG(); > + break; > + } > + cond_resched(); > + ret = 0; > + }
get_user_pages() is really the wrong thing to use here. It makes pages *present* so that we can do things like hand them off to a driver. For checkpointing, we really don't care about that. It's a waste of time, for instance to perform faults to fill the mappings up with zero pages and page tables. Just think of what will happen the first time we touch a very large, very sparse anonymous area. We'll probably kill the system just allocating page tables. Take a look at the comment in follow_page(). This is a similar operation to core dumping, and we need to be careful.
This might be fine for a proof of concept, but it needs to be thought out much more thoroughly before getting merged. I guess I'm volunteering to go do that.
-- Dave
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