Messages in this thread | | | Date | Wed, 23 Mar 2022 16:48:57 -0700 | Subject | Re: [RFC PATCH 10/47] mm: asi: Support for global non-sensitive direct map allocations | From | Junaid Shahid <> |
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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).
>> @@ -542,6 +545,12 @@ TESTCLEARFLAG(Young, young, PF_ANY) >> PAGEFLAG(Idle, idle, PF_ANY) >> #endif >> >> +#ifdef CONFIG_ADDRESS_SPACE_ISOLATION >> +__PAGEFLAG(GlobalNonSensitive, global_nonsensitive, PF_ANY); > > Why is PF_ANY appropriate? >
I think we actually can use PF_HEAD here. That would make the alloc_pages path faster too. I'll change to that. (Initially I had gone with PF_ANY because in theory, you could allocate a compound page and then break it later and free the individual pages, but I don't know if that actually happens apart from THP, and certainly doesn't look like the case for any of the stuff that we have marked as non-sensitive.)
Thanks, Junaid
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