compaction

Linux 6.18.37 LTS: mm/compaction.c
Linux 6.18.37 LTS: mm/migrate.c
Linux 6.18.37 LTS: include/linux/compaction.h

		(cc->mode != MIGRATE_SYNC ? ISOLATE_ASYNC_MIGRATE : 0);
	bool fast_find_block;

	/*
	 * Start at where we last stopped, or beginning of the zone as
	 * initialized by compact_zone(). The first failure will use
	 * the lowest PFN as the starting point for linear scanning.
	 */
	low_pfn = fast_find_migrateblock(cc);
	block_start_pfn = pageblock_start_pfn(low_pfn);
	if (block_start_pfn < cc->zone->zone_start_pfn)
		block_start_pfn = cc->zone->zone_start_pfn;

	/*
	 * fast_find_migrateblock() has already ensured the pageblock is not
	 * set with a skipped flag, so to avoid the isolation_suitable check
	 * below again, check whether the fast search was successful.
	 */
	fast_find_block = low_pfn != cc->migrate_pfn && !cc->fast_search_fail;

	/* Only scan within a pageblock boundary */
	block_end_pfn = pageblock_end_pfn(low_pfn);

	/*
	 * Iterate over whole pageblocks until we find the first suitable.
	 * Do not cross the free scanner.
	 */
	for (; block_end_pfn <= cc->free_pfn;
			fast_find_block = false,
			cc->migrate_pfn = low_pfn = block_end_pfn,
			block_start_pfn = block_end_pfn,
			block_end_pfn += pageblock_nr_pages) {

		/*
		 * This can potentially iterate a massively long zone with
		 * many pageblocks unsuitable, so periodically check if we
		 * need to schedule.
		 */
		if (!(low_pfn % (COMPACT_CLUSTER_MAX * pageblock_nr_pages)))
			cond_resched();

	VM_BUG_ON(!list_empty(&cc->migratepages));

	return ret;
}

static enum compact_result compact_zone_order(struct zone *zone, int order,
		gfp_t gfp_mask, enum compact_priority prio,
		unsigned int alloc_flags, int highest_zoneidx,
		struct page **capture)
{
	enum compact_result ret;
	struct compact_control cc = {
		.order = order,
		.search_order = order,
		.gfp_mask = gfp_mask,
		.zone = zone,
		.mode = (prio == COMPACT_PRIO_ASYNC) ?
					MIGRATE_ASYNC :	MIGRATE_SYNC_LIGHT,
		.alloc_flags = alloc_flags,
		.highest_zoneidx = highest_zoneidx,
		.direct_compaction = true,
		.whole_zone = (prio == MIN_COMPACT_PRIORITY),
		.ignore_skip_hint = (prio == MIN_COMPACT_PRIORITY),
		.ignore_block_suitable = (prio == MIN_COMPACT_PRIORITY)
	};
	struct capture_control capc = {
		.cc = &cc,
		.page = NULL,
	};

	/*
	 * Make sure the structs are really initialized before we expose the
	 * capture control, in case we are interrupted and the interrupt handler
	 * frees a page.
	 */
	barrier();
	WRITE_ONCE(current->capture_control, &capc);

	ret = compact_zone(&cc, &capc);