How to find or calculate a Linux process's page table size and other kernel accounting?

Question

How can I find out how big a Linux process's page table is, along with any other variable-size process accounting?

Solution 1

If you are really interested in the page tables, do a

$ cat /proc/meminfo | grep PageTables
PageTables:      24496 kB

Solution 2

Since Linux 2.6.10, the amount of memory used by a single process' page tables has been exposed via the VmPTE field of /proc/<pid>/status.

Solution 3

Not sure about Linux, but most UNIX variants provide sysctl(3) for this purpose. There is also the sysctl(8) command line utility.

Solution 4

Hmmm, back in Ye Olden Tymes, we used to call nlist(3) to get the system address for the data we were interested in, then open /dev/kmem, seek to the address, then read the data. Not sure if this works in Linux, but it might be worth typing "man 3 nlist" and seeing what comes back.

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Comments

[Reed Hedges]

This is useful, but I need to find out whether this size is "too big". If there is a limit to this size that would call fork() to fail, and how close to that limit is the kernel. Ideally, I would also need to find out what portion of that PageTables size is being used by a specific process, such that when fork() tries to copy the tables for that process, the limit would be exceeded.

[Prashant]

What Unix allows you to read the pagetablesize (opposed to pagesize) via sysctl?

[Prashant]

Oh BTW, some numbers with Huge pages now: kevinclosson.wordpress.com/2009/07/28/…

[Tom Cornebize]

It seems to work well, except when I allocate huge pages with mmap: the size reported is a small constant, no matter the size of the allocation (kernel 4.4.0-77).

[Tom Cornebize]

The value reported by the field VmPMD seems ok, it grows linearly with the size of the allocation, even with huge pages. But I don't think it accounts for the whole page table (the man says "Size of second-level page tables"). When experimenting with classical pages, this value is approximately 500 times lower than VmPTE.