reclaim

Linux 6.18.37 LTS: mm/vmscan.c
Linux 6.18.37 LTS: mm/workingset.c
Linux 6.18.37 LTS: mm/shrinker.c

static void shrink_node(pg_data_t *pgdat, struct scan_control *sc)
{
	unsigned long nr_reclaimed, nr_scanned, nr_node_reclaimed;
	struct lruvec *target_lruvec;
	bool reclaimable = false;

	if (lru_gen_enabled() && root_reclaim(sc)) {
		memset(&sc->nr, 0, sizeof(sc->nr));
		lru_gen_shrink_node(pgdat, sc);
		return;
	}

	target_lruvec = mem_cgroup_lruvec(sc->target_mem_cgroup, pgdat);

again:
	memset(&sc->nr, 0, sizeof(sc->nr));

	nr_reclaimed = sc->nr_reclaimed;
	nr_scanned = sc->nr_scanned;

	prepare_scan_control(pgdat, sc);

	shrink_node_memcgs(pgdat, sc);

static int kswapd(void *p)
{
	unsigned int alloc_order, reclaim_order;
	unsigned int highest_zoneidx = MAX_NR_ZONES - 1;
	pg_data_t *pgdat = (pg_data_t *)p;
	struct task_struct *tsk = current;

	/*
	 * Tell the memory management that we're a "memory allocator",
	 * and that if we need more memory we should get access to it
	 * regardless (see "__alloc_pages()"). "kswapd" should
	 * never get caught in the normal page freeing logic.
	 *
	 * (Kswapd normally doesn't need memory anyway, but sometimes
	 * you need a small amount of memory in order to be able to
	 * page out something else, and this flag essentially protects
	 * us from recursively trying to free more memory as we're
	 * trying to free the first piece of memory in the first place).
	 */
	tsk->flags |= PF_MEMALLOC | PF_KSWAPD;
	set_freezable();

	WRITE_ONCE(pgdat->kswapd_order, 0);
	WRITE_ONCE(pgdat->kswapd_highest_zoneidx, MAX_NR_ZONES);
	atomic_set(&pgdat->nr_writeback_throttled, 0);
	for ( ; ; ) {
		bool was_frozen;

		alloc_order = reclaim_order = READ_ONCE(pgdat->kswapd_order);
		highest_zoneidx = kswapd_highest_zoneidx(pgdat,
							highest_zoneidx);

kswapd_try_sleep:
		kswapd_try_to_sleep(pgdat, alloc_order, reclaim_order,
					highest_zoneidx);

		/* Read the new order and highest_zoneidx */
		alloc_order = READ_ONCE(pgdat->kswapd_order);
		highest_zoneidx = kswapd_highest_zoneidx(pgdat,
							highest_zoneidx);
		WRITE_ONCE(pgdat->kswapd_order, 0);
		WRITE_ONCE(pgdat->kswapd_highest_zoneidx, MAX_NR_ZONES);

		if (kthread_freezable_should_stop(&was_frozen))
			break;

		/*
		 * We can speed up thawing tasks if we don't call balance_pgdat
		 * after returning from the refrigerator
		 */
		if (was_frozen)
			continue;

		/*
		 * Reclaim begins at the requested order but if a high-order
		 * reclaim fails then kswapd falls back to reclaiming for
		 * order-0. If that happens, kswapd will consider sleeping
		 * for the order it finished reclaiming at (reclaim_order)
		 * but kcompactd is woken to compact for the original
		 * request (alloc_order).
		 */
		trace_mm_vmscan_kswapd_wake(pgdat->node_id, highest_zoneidx,
						alloc_order);
		reclaim_order = balance_pgdat(pgdat, alloc_order,
						highest_zoneidx);
		if (reclaim_order < alloc_order)
			goto kswapd_try_sleep;
	}

	tsk->flags &= ~(PF_MEMALLOC | PF_KSWAPD);

	return 0;
}