VM Probes

The virtual memory subsystem (VM) probes provide information on page faults, page I/O, the page daemon, and the swapper.

Page Faults

Page fault probes relate virtual addresses with fault types and with files (vnodes).

The address_fault probe traces address-space faults; it records the faulting virtual address, the type of fault, and the desired access protection.

The fault type and access type values use the constants defined in <vm/seg_enum.h>. Fault types are invalid page (minor fault), protection fault, or software requests to lock and unlock pages for physical I/O (softlock and softunlock). Access types are read, write, execute and create.

The major_fault probe traces major page faults; it records the vnode and offset (which together identify a file system page) from which the fault should be resolved. This data can be correlated with the immediately preceding address_fault event for the current thread to obtain the faulting virtual address.

The anon_private probe traces copy-on-write faults.

The anon_zero probe traces zero-fill faults.

The page_unmap probe marks the dissociation between a physical page and a file system page (for example, when a page is renamed or destroyed).

Page I/O

The pagein probe traces the initiation of a pagein request; it records the vnode, offset, and size of the pagein.

The pageout probe traces the completion of a pageout request; it records the number of pages paged out, the number of pages freed, and the number of pages reclaimed after the pageout.

Page Daemon

Iterations of the page daemon (page stealer) are traced by two probes: pageout_scan_start and pageout_scan_end. The probes report the number of free pages needed before the scan, the number of pages examined during the scan, and the free page counts before and after the scan. Potentially, more pages are freed when pageout requests queued by the scan are completed.

Swapper

Three probes trace the activity of the swapper.

• The swapout_process probe traces the swapping out of a process address space; it records the process identifier and the total number of pages either freed or queued for output.

• The swapout_lwp probe traces the swapping out of an LWP's stack pages; it records the LWP's identity and the number of pages queued for output.

• The swapin_lwp probe traces the swapping in of an LWP's stack pages; it records the LWP's identity and the number of stack pages brought in.