Start_Kernel 2 (Week 1)

floatFirstTOC: right

dd

/*
 * This is the main entry point to direct page reclaim.
 *
 * If a full scan of the inactive list fails to free enough memory then we
 * are "out of memory" and something needs to be killed.
 *
 * If the caller is !__GFP_FS then the probability of a failure is reasonably
 * high - the zone may be full of dirty or under-writeback pages, which this
 * caller can't do much about.  We kick the writeback threads and take explicit
 * naps in the hope that some of these pages can be written.  But if the
 * allocating task holds filesystem locks which prevent writeout this might not
 * work, and the allocation attempt will fail.
 *
 * returns:	0, if no pages reclaimed
 * 		else, the number of pages reclaimed
 */
static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
					  struct scan_control *sc)
{
	int initial_priority = sc->priority;
	pg_data_t *last_pgdat;
	struct zoneref *z;
	struct zone *zone;
retry:
	delayacct_freepages_start();

	if (!cgroup_reclaim(sc))
		__count_zid_vm_events(ALLOCSTALL, sc->reclaim_idx, 1);

	do {
		if (!sc->proactive)
			vmpressure_prio(sc->gfp_mask, sc->target_mem_cgroup,
					sc->priority);
		sc->nr_scanned = 0;
		shrink_zones(zonelist, sc);

		if (sc->nr_reclaimed >= sc->nr_to_reclaim)
			break;

		if (sc->compaction_ready)
			break;

		/*
		 * If we're getting trouble reclaiming, start doing
		 * writepage even in laptop mode.
		 */
		if (sc->priority < DEF_PRIORITY - 2)
			sc->may_writepage = 1;
	} while (--sc->priority >= 0);

	last_pgdat = NULL;
	for_each_zone_zonelist_nodemask(zone, z, zonelist, sc->reclaim_idx,
					sc->nodemask) {
		if (zone->zone_pgdat == last_pgdat)
			continue;
		last_pgdat = zone->zone_pgdat;

		snapshot_refaults(sc->target_mem_cgroup, zone->zone_pgdat);

		if (cgroup_reclaim(sc)) {
			struct lruvec *lruvec;

			lruvec = mem_cgroup_lruvec(sc->target_mem_cgroup,
						   zone->zone_pgdat);
			clear_bit(LRUVEC_CGROUP_CONGESTED, &lruvec->flags);
		}
	}

	delayacct_freepages_end();

	if (sc->nr_reclaimed)
		return sc->nr_reclaimed;

	/* Aborted reclaim to try compaction? don't OOM, then */
	if (sc->compaction_ready)
		return 1;

	/*
	 * We make inactive:active ratio decisions based on the node's
	 * composition of memory, but a restrictive reclaim_idx or a
	 * memory.low cgroup setting can exempt large amounts of
	 * memory from reclaim. Neither of which are very common, so
	 * instead of doing costly eligibility calculations of the
	 * entire cgroup subtree up front, we assume the estimates are
	 * good, and retry with forcible deactivation if that fails.
	 */
	if (sc->skipped_deactivate) {
		sc->priority = initial_priority;
		sc->force_deactivate = 1;
		sc->skipped_deactivate = 0;
		goto retry;
	}

	/* Untapped cgroup reserves?  Don't OOM, retry. */
	if (sc->memcg_low_skipped) {
		sc->priority = initial_priority;
		sc->force_deactivate = 0;
		sc->memcg_low_reclaim = 1;
		sc->memcg_low_skipped = 0;
		goto retry;
	}

	return 0;
}

This is the main entry point to direct page reclaim.

If a full scan of the inactive list fails to free enough memory then we
are "out of memory" and something needs to be killed.

매개변수

반환값

콜 스택

do {
		if (!sc->proactive)
			vmpressure_prio(sc->gfp_mask, sc->target_mem_cgroup,
					sc->priority);
		sc->nr_scanned = 0;
		shrink_zones(zonelist, sc);

		if (sc->nr_reclaimed >= sc->nr_to_reclaim)
			break;

		if (sc->compaction_ready)
			break;

		/*
		 * If we're getting trouble reclaiming, start doing
		 * writepage even in laptop mode.
		 */
		if (sc->priority < DEF_PRIORITY - 2)
			sc->may_writepage = 1;
	} while (--sc->priority >= 0);

if (!sc->proactive)
			vmpressure_prio(sc->gfp_mask, sc->target_mem_cgroup,
					sc->priority);

sc->nr_scanned = 0;
shrink_zones(zonelist, sc);

if (sc->nr_reclaimed >= sc->nr_to_reclaim)
			break;

if (sc->compaction_ready)
			break;

		/*
		 * If we're getting trouble reclaiming, start doing
		 * writepage even in laptop mode.
		 */
		if (sc->priority < DEF_PRIORITY - 2)
			sc->may_writepage = 1;

shrink_zones()

	/*
	 * If the number of buffer_heads in the machine exceeds the maximum
	 * allowed level, force direct reclaim to scan the highmem zone as
	 * highmem pages could be pinning lowmem pages storing buffer_heads
	 */
	orig_mask = sc->gfp_mask;
	if (buffer_heads_over_limit) {
		sc->gfp_mask |= __GFP_HIGHMEM;
		sc->reclaim_idx = gfp_zone(sc->gfp_mask);
	}

	for_each_zone_zonelist_nodemask(zone, z, zonelist,
					sc->reclaim_idx, sc->nodemask) {
					...
					}

/**
 * for_each_zone_zonelist_nodemask - helper macro to iterate over valid zones in a zonelist at or below a given zone index and within a nodemask
 * @zone: The current zone in the iterator
 * @z: The current pointer within zonelist->_zonerefs being iterated
 * @zlist: The zonelist being iterated
 * @highidx: The zone index of the highest zone to return
 * @nodemask: Nodemask allowed by the allocator
 *
 * This iterator iterates though all zones at or below a given zone index and
 * within a given nodemask
 */
#define for_each_zone_zonelist_nodemask(zone, z, zlist, highidx, nodemask) \
	for (z = first_zones_zonelist(zlist, highidx, nodemask), zone = zonelist_zone(z);	\
		zone;							\
		z = next_zones_zonelist(++z, highidx, nodemask),	\
			zone = zonelist_zone(z))

#define for_next_zone_zonelist_nodemask(zone, z, highidx, nodemask) \
	for (zone = z->zone;	\
		zone;							\
		z = next_zones_zonelist(++z, highidx, nodemask),	\
			zone = zonelist_zone(z))

	   /*
		 * Take care memory controller reclaiming has small influence
		 * to global LRU.
		 */
		if (!cgroup_reclaim(sc)) {

	/*
	 * The memory cgroup that hit its limit and as a result is the
	 * primary target of this reclaim invocation.
	 */
	struct mem_cgroup *target_mem_cgroup;

			if (!cpuset_zone_allowed(zone,
						 GFP_KERNEL | __GFP_HARDWALL))
				continue;

			/*
			 * If we already have plenty of memory free for
			 * compaction in this zone, don't free any more.
			 * Even though compaction is invoked for any
			 * non-zero order, only frequent costly order
			 * reclamation is disruptive enough to become a
			 * noticeable problem, like transparent huge
			 * page allocations.
			 */
			if (IS_ENABLED(CONFIG_COMPACTION) &&
			    sc->order > PAGE_ALLOC_COSTLY_ORDER &&
			    compaction_ready(zone, sc)) {
				sc->compaction_ready = true;
				continue;

			/*
			 * Shrink each node in the zonelist once. If the
			 * zonelist is ordered by zone (not the default) then a
			 * node may be shrunk multiple times but in that case
			 * the user prefers lower zones being preserved.
			 */
			if (zone->zone_pgdat == last_pgdat)
				continue;

			/*
			 * This steals pages from memory cgroups over softlimit
			 * and returns the number of reclaimed pages and
			 * scanned pages. This works for global memory pressure
			 * and balancing, not for a memcg's limit.
			 */
			nr_soft_scanned = 0;
			nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone->zone_pgdat,
						sc->order, sc->gfp_mask,
						&nr_soft_scanned);
			sc->nr_reclaimed += nr_soft_reclaimed;
			sc->nr_scanned += nr_soft_scanned;
		 /* need some check for avoid more shrink_zone() */

		if (!first_pgdat)
			first_pgdat = zone->zone_pgdat;

		/* See comment about same check for global reclaim above */
		if (zone->zone_pgdat == last_pgdat)
			continue;
		last_pgdat = zone->zone_pgdat;
		shrink_node(zone->zone_pgdat, sc);

	if (first_pgdat)
		consider_reclaim_throttle(first_pgdat, sc);

	/*
	 * Restore to original mask to avoid the impact on the caller if we
	 * promoted it to __GFP_HIGHMEM.
	 */
	sc->gfp_mask = orig_mask;