linux-5.15/get_page_from_freelist() の履歴(No.1)

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• linux-5.15/get_page_from_freelist() へ行く。
  • 1 (2025-09-12 (金) 15:16:49)

---

参照元†

• linux-5.15/compaction_deferred()

説明†

• パス: linux-5.15/mm/page_alloc.c

• FIXME: これは何？
  • 説明

引数†

返り値†

参考†

実装†

/*
 * get_page_from_freelist goes through the zonelist trying to allocate
 * a page.
 */
static struct page *
get_page_from_freelist(gfp_t gfp_mask, unsigned int order, int alloc_flags,
						const struct alloc_context *ac)
{
	struct zoneref *z;
	struct zone *zone;
	struct pglist_data *last_pgdat_dirty_limit = NULL;
	bool no_fallback;

• • linux-5.15/zoneref
  • linux-5.15/zone
  • linux-5.15/pglist_data

retry:
	/*
	 * Scan zonelist, looking for a zone with enough free.
	 * See also __cpuset_node_allowed() comment in kernel/cpuset.c.
	 */
	no_fallback = alloc_flags & ALLOC_NOFRAGMENT;
	z = ac->preferred_zoneref;
	for_next_zone_zonelist_nodemask(zone, z, ac->highest_zoneidx,
					ac->nodemask) {
		struct page *page;
		unsigned long mark;

		if (cpusets_enabled() &&
			(alloc_flags & ALLOC_CPUSET) &&
			!__cpuset_zone_allowed(zone, gfp_mask))
				continue;

• • linux-5.15/for_next_zone_zonelist_nodemask()
  • linux-5.15/page
  • linux-5.15/cpusets_enabled()
  • linux-5.15/__cpuset_zone_allowed()

		/*
		 * When allocating a page cache page for writing, we
		 * want to get it from a node that is within its dirty
		 * limit, such that no single node holds more than its
		 * proportional share of globally allowed dirty pages.
		 * The dirty limits take into account the node's
		 * lowmem reserves and high watermark so that kswapd
		 * should be able to balance it without having to
		 * write pages from its LRU list.
		 *
		 * XXX: For now, allow allocations to potentially
		 * exceed the per-node dirty limit in the slowpath
		 * (spread_dirty_pages unset) before going into reclaim,
		 * which is important when on a NUMA setup the allowed
		 * nodes are together not big enough to reach the
		 * global limit.  The proper fix for these situations
		 * will require awareness of nodes in the
		 * dirty-throttling and the flusher threads.
		 */
		if (ac->spread_dirty_pages) {
			if (last_pgdat_dirty_limit == zone->zone_pgdat)
				continue;

			if (!node_dirty_ok(zone->zone_pgdat)) {
				last_pgdat_dirty_limit = zone->zone_pgdat;
				continue;
			}
		}

• • linux-5.15/node_dirty_ok()

		if (no_fallback && nr_online_nodes > 1 &&
		    zone != ac->preferred_zoneref->zone) {
			int local_nid;

			/*
			 * If moving to a remote node, retry but allow
			 * fragmenting fallbacks. Locality is more important
			 * than fragmentation avoidance.
			 */
			local_nid = zone_to_nid(ac->preferred_zoneref->zone);
			if (zone_to_nid(zone) != local_nid) {
				alloc_flags &= ~ALLOC_NOFRAGMENT;
				goto retry;
			}
		}

• • linux-5.15/zone_to_nid()

		mark = wmark_pages(zone, alloc_flags & ALLOC_WMARK_MASK);
		if (!zone_watermark_fast(zone, order, mark,
				       ac->highest_zoneidx, alloc_flags,
				       gfp_mask)) {
			int ret;

• • linux-5.15/wmark_pages()
  • linux-5.15/zone_watermark_fast()

#ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT
			/*
			 * Watermark failed for this zone, but see if we can
			 * grow this zone if it contains deferred pages.
			 */
			if (static_branch_unlikely(&deferred_pages)) {
				if (_deferred_grow_zone(zone, order))
					goto try_this_zone;
			}
#endif

• • linux-5.15/static_branch_unlikely()
  • linux-5.15/_deferred_grow_zone()

			/* Checked here to keep the fast path fast */
			BUILD_BUG_ON(ALLOC_NO_WATERMARKS < NR_WMARK);
			if (alloc_flags & ALLOC_NO_WATERMARKS)
				goto try_this_zone;

			if (!node_reclaim_enabled() ||
			    !zone_allows_reclaim(ac->preferred_zoneref->zone, zone))
				continue;

• • linux-5.15/BUILD_BUG_ON()
  • linux-5.15/node_reclaim_enabled()
  • linux-5.15/zone_allows_reclaim()

			ret = node_reclaim(zone->zone_pgdat, gfp_mask, order);
			switch (ret) {
			case NODE_RECLAIM_NOSCAN:
				/* did not scan */
				continue;
			case NODE_RECLAIM_FULL:
				/* scanned but unreclaimable */
				continue;
			default:
				/* did we reclaim enough */
				if (zone_watermark_ok(zone, order, mark,
					ac->highest_zoneidx, alloc_flags))
					goto try_this_zone;

				continue;
			}
		}

• • linux-5.15/node_reclaim()
  • linux-5.15/zone_watermark_ok()

try_this_zone:
		page = rmqueue(ac->preferred_zoneref->zone, zone, order,
				gfp_mask, alloc_flags, ac->migratetype);
		if (page) {
			prep_new_page(page, order, gfp_mask, alloc_flags);

			/*
			 * If this is a high-order atomic allocation then check
			 * if the pageblock should be reserved for the future
			 */
			if (unlikely(order && (alloc_flags & ALLOC_HARDER)))
				reserve_highatomic_pageblock(page, zone, order);

			return page;

• • linux-5.15/rmqueue()
  • linux-5.15/prep_new_page()
  • linux-5.15/unlikely()
  • linux-5.15/reserve_highatomic_pageblock()

		} else {
#ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT
			/* Try again if zone has deferred pages */
			if (static_branch_unlikely(&deferred_pages)) {
				if (_deferred_grow_zone(zone, order))
					goto try_this_zone;
			}
#endif
		}
	}

• • linux-5.15/static_branch_likely()
  • linux-5.15/_deferred_grow_zone()

	/*
	 * It's possible on a UMA machine to get through all zones that are
	 * fragmented. If avoiding fragmentation, reset and try again.
	 */
	if (no_fallback) {
		alloc_flags &= ~ALLOC_NOFRAGMENT;
		goto retry;
	}

	return NULL;
}

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