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

• 履歴一覧
• 差分 を表示
• 現在との差分 を表示
• ソース を表示
• linux-5.15/__compaction_suitable() へ行く。
  • 1 (2025-09-10 (水) 16:47:47)
  • 2 (2025-09-10 (水) 16:51:11)

参照元†

• linux-5.15/compaction_suitable()

説明†

• パス: [[linux-5.15/]]

• FIXME: これは何？
  • 説明

引数†

返り値†

参考†

実装†

static enum compact_result __compaction_suitable(struct zone *zone, int order,
					unsigned int alloc_flags,
					int highest_zoneidx,
					unsigned long wmark_target)
{
	unsigned long watermark;

	if (is_via_compact_memory(order))
		return COMPACT_CONTINUE;

	//★★2番目の引数の意味: ALLOC_WMARK_MASK = 4 - 1 = 3で、
	//★★alloc_flagsのビットフィールド0~1の値を取得します。値はstruct zoneの
	//★★配列_watermarkの添字にします。値の意味はenum zone_watermarksと同じで、
	//★★下記の通りです。
	//★★  0: min   = WMARK_MIN
	//★★  1: low   = WMARK_LOW
	//★★  2: high  = WMARK_HIGH
	//★★  3: 使わない
	watermark = wmark_pages(zone, alloc_flags & ALLOC_WMARK_MASK);
	/*
	 * If watermarks for high-order allocation are already met, there
	 * should be no need for compaction at all.
	 */
	if (zone_watermark_ok(zone, order, watermark, highest_zoneidx,
								alloc_flags))
		return COMPACT_SUCCESS;

	/*
	 * Watermarks for order-0 must be met for compaction to be able to
	 * isolate free pages for migration targets. This means that the
	 * watermark and alloc_flags have to match, or be more pessimistic than
	 * the check in __isolate_free_page(). We don't use the direct
	 * compactor's alloc_flags, as they are not relevant for freepage
	 * isolation. We however do use the direct compactor's highest_zoneidx
	 * to skip over zones where lowmem reserves would prevent allocation
	 * even if compaction succeeds.
	 * For costly orders, we require low watermark instead of min for
	 * compaction to proceed to increase its chances.
	 * ALLOC_CMA is used, as pages in CMA pageblocks are considered
	 * suitable migration targets
	 */
	watermark = (order > PAGE_ALLOC_COSTLY_ORDER) ?
				low_wmark_pages(zone) : min_wmark_pages(zone);
	watermark += compact_gap(order);
	if (!__zone_watermark_ok(zone, 0, watermark, highest_zoneidx,
						ALLOC_CMA, wmark_target))
		return COMPACT_SKIPPED;

	return COMPACT_CONTINUE;
}

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