Messages in this thread | ![/](/images/icornerl.gif) | | Date | Wed, 23 Mar 2022 18:54:37 -0700 | Subject | Re: [RFC PATCH 10/47] mm: asi: Support for global non-sensitive direct map allocations | From | Junaid Shahid <> |
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On 3/23/22 16:48, Junaid Shahid wrote: > Hi Matthew, > > On 3/23/22 14:06, Matthew Wilcox wrote: >> On Tue, Feb 22, 2022 at 09:21:46PM -0800, Junaid Shahid wrote: >>> standard ASI instances. A new page flag is also added so that when >>> these pages are freed, they can also be unmapped from the ASI page >>> tables. >> >> It's cute how you just throw this in as an aside. Page flags are >> in high demand and just adding them is not to be done lightly. Is >> there any other way of accomplishing what you want? >> > > I suppose we may be able to use page_ext instead. That certainly should be > feasible for the PG_local_nonsensitive flag introduced in a later patch, > although I am not completely sure about the PG_global_nonsensitive flag. That > could get slightly tricky (though likely still possible to do) in case we need > to allocate any non-sensitive memory before page_ext is initialized. One concern > with using page_ext could be the extra memory usage on large machines. > > BTW is page flag scarcity an issue on 64-bit systems as well, or only 32-bit > systems? ASI is only supported on 64-bit systems (at least currently). >
One other thing that we could do to remove the need for the PG_global_nonsensitive flag altogether (though not the PG_local_nonsensitive flag) would be to always try to unmap pages from the asi_global_nonsensitive_pgd in free_pages(). Basically, that would mean adding a page table walk to every free_pages() rather than just non-sensitive free_pages(). Do you think that may be a better trade-off in order to avoid the flag?
Thanks, Junaid
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