A Thief in the Night: vhand
The vhand kernel daemon is actually two operations in a single package. The first scan targets pages and, if their pde_accessed bits are still clean, steals them; the second scan ages targeted pages. To age a page means to invalidate its current virtual address translation(s) in all processor TLBs and clear the access bit for the page in its hashtable entry (pde_accessed = 0). vhand steals a page when it discovers that the page has not been referenced since it was last scanned. It then requests a page-out and allocates a swap location if one does not already exist for the page.
Pages are aged and stolen through their pregion region vfd linkages. Figure 7-2 shows vhand's view of a pregion.
Figure 7-2. Inside Each ...
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