[Xen-devel] Three Xenpaging design questions

[Gage Eads <geads@xxxxxxxxxxxxxxxxx>]

Hi, I've been fiddling with the xenpaging source recently, and I have a few questions regarding it.

1. file_op() vs. pread() and pwrite(): is there any reason file_op is used instead of pread and pwrite? Just curious.

2. Separation of policy and mechanism: I appreciate that the logic for selecting victim pages is separated from the eviction mechanism. However the policy abstraction is somewhat broken in two ways: policy_notify_paged_in_nomru() exposes the use of an mru list, and xenpaging_resume_page() contains logic that decides whether to add the gfn to the mru list. The mru list is a policy detail that shouldn't be exposed to the mechanism layer (even if the mru list doesn't actually influence default policy's decisions, as is currently the case).

I bring this up because I'd like to experiment with different policies. Are there any reasons (or flaws in my reasoning) why I shouldn't fix the identified issues with the policy abstractoin?

3. memory/target-tot_pages: from the name, one would assume this value sets a limit of the number of memory pages in a VM. Specifically, the number of 4 KB pages in the VM. Instead, target-tot_pages is a memory limit in KiB. I found this fairly misleading, but perhaps I am in the minority. Is there any interest in either renaming this value or removing the KiB to pages conversion so that its behavior more accurately reflects its name?

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