CODEWITHSUNDEEP
linux-kernelkernel-modulepage-tables
Reza
Reza

Reputation: 11

UNIX system call to unset the reference bit of a specific page in page table?

I'm trying to count hits of a specific set of pages, by hacking the reference bits in the page table. Is there any system call or any other way to unset reference bits (in UNIX-like systems)?

A page table is the data structure used by a virtual memory system in a computer operating system to store the mapping between virtual addresses and physical addresses. (https://en.wikipedia.org/wiki/Page_table)

In unix-like systems there is a bit associated with each page table entry, called "reference" bit, which indicates if a page was accessed since the bit was unset. The linux kernel unsets these reference bits periodically and checks a while after that to know what pages have been accessed, in order to detect "hot" pages. But this information is very coarse grain and low-precision since it doesn't say anything about the number of accesses and their time.

I want to count accesses to specific pages during shorter epochs by unsetting reference bits then check if the pages have been accessed after a short time.

Therefore, I was wondering if there is any system call or CPU interrupt which provides means to unset "reference bits". Otherwise, I need to dive deep into kernel to see what goes on down there.

Upvotes: 0

Views: 204

Answers (1)

wallyk
wallyk

Reputation: 57784

There is no API for resetting the page reference bits. Page management is a very twitchy aspect of kernel tuning and no one wants to upset it. Of course you could modify the kernel to your needs.

Instead, you might look into Valgrind which is a debugging and profiling tool for running a single program. Ordinarily it detects subtle memory errors such as detecting use of a dynamic memory block after it has been freed.

If you need page management information for the system as a whole, I think the most expedient solution is hacking the kernel.

Upvotes: 1

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