Linux Kernel Architecture

Chapter 18: Page Reclaim and Swapping

thatrefill_inactive_zoneis among the longer functions in the kernel. It performs the following
principal steps:

1. It copies the required number of pages defined bynr_pagesfrom theactivelist to a tempo-
   rary, local list usingisolate_lru_pages.


2. It distributes the pages over the active and inactive lists according to their activity level.


3. It frees unimportant pages in bundles.

Figure 18-15 shows the code flow diagram for the firstrefill_inactive_zonestep.

Compute Swap Parameters

refill_inactive_zone

Part2

lru_add_drain

isolate_lru_pages

Figure 18-15: Code flow diagram for

refill_inactive_zone(Part 1).

First of all, the kernel calculates a few parameters to define the aggressiveness and the behavior of the
page reclaim algorithm. Some statistical data are analyzed:

mm/vmscan.c

...

distress = 100 >> min(zone->prev_priority, priority);

mapped_ratio = ((global_page_state(NR_FILE_MAPPED) +

global_page_state(NR_ANON_PAGES)) * 100) /

vm_total_pages;

mapped_ratio = (sc->nr_mapped * 100) / total_memory;

swap_tendency = mapped_ratio / 2 + distress + sc->swappiness;

imbalance = zone_page_state(zone, NR_ACTIVE);

imbalance /= zone_page_state(zone, NR_INACTIVE) + 1;

imbalance *= (vm_swappiness + 1);

imbalance /= 100;

imbalance *= mapped_ratio;

imbalance /= 100;

swap_tendency += imbalance;

if (swap_tendency >= 100)

reclaim_mapped = 1;

...