struct zone {

unsigned long nr_scan_active;

unsigned long nr_scan_inactive;

unsigned long pages_scanned;

atomic_long_t vm_stat[NR_VM_ZONE_STAT_ITEMS];

The kernel needs to scan the active and inactive lists to find pages that can be moved between the lists, or that can be reclaimed from the inactive list. However, the complete lists are not scanned in each pass, but only nr_scan_active elements on the active, and nr_scan_inactive on the inactive list. Since the kernel uses an LRU scheme, the number is counted from the tail of the list. pages_scanned remembers how many pages were scanned in the previous reclaim pass, and vm_stat provides statistical information about the zone, for instance, the number of currently active and inactive pages. Recall that the statistical elements can be accessed with the auxiliary function zone_page_state.

Continue reading here: Mmvmscanc

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