compaction

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

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);

	trace_mm_compaction_begin(cc, start_pfn, end_pfn, sync);

	/* lru_add_drain_all could be expensive with involving other CPUs */
	lru_add_drain();

	while ((ret = compact_finished(cc)) == COMPACT_CONTINUE) {
		int err;
		unsigned long iteration_start_pfn = cc->migrate_pfn;

		/*
		 * Avoid multiple rescans of the same pageblock which can
		 * happen if a page cannot be isolated (dirty/writeback in
		 * async mode) or if the migrated pages are being allocated
		 * before the pageblock is cleared.  The first rescan will
		 * capture the entire pageblock for migration. If it fails,
		 * it'll be marked skip and scanning will proceed as normal.
		 */
		cc->finish_pageblock = false;
		if (pageblock_start_pfn(last_migrated_pfn) ==
		    pageblock_start_pfn(iteration_start_pfn)) {
			cc->finish_pageblock = true;
		}

rescan:
		switch (isolate_migratepages(cc)) {
		case ISOLATE_ABORT:
			ret = COMPACT_CONTENDED;
			putback_movable_pages(&cc->migratepages);
			cc->nr_migratepages = 0;
			goto out;
		case ISOLATE_NONE:
			if (update_cached) {
				cc->zone->compact_cached_migrate_pfn[1] =
					cc->zone->compact_cached_migrate_pfn[0];
			}

			/*
			 * We haven't isolated and migrated anything, but
			 * there might still be unflushed migrations from
			 * previous cc->order aligned block.
			 */
			goto check_drain;
		case ISOLATE_SUCCESS:
			update_cached = false;
			last_migrated_pfn = max(cc->zone->zone_start_pfn,
				pageblock_start_pfn(cc->migrate_pfn - 1));
		}

		/*
		 * Record the number of pages to migrate since the
		 * compaction_alloc/free() will update cc->nr_migratepages
		 * properly.
		 */
		nr_migratepages = cc->nr_migratepages;
		err = migrate_pages(&cc->migratepages, compaction_alloc,
				compaction_free, (unsigned long)cc, cc->mode,
				MR_COMPACTION, &nr_succeeded);