【Linux 内核 内存管理】物理分配页 ⑨ ( __alloc_pages_slowpath 慢速路径调用函数源码分析 | retry 标号代码分析 )

retry:
	/* Ensure kswapd doesn't accidentally go to sleep as long as we loop */
	if (gfp_mask & __GFP_KSWAPD_RECLAIM)
		wake_all_kswapds(order, ac);

	/* Attempt with potentially adjusted zonelist and alloc_flags */
	page = get_page_from_freelist(gfp_mask, order, alloc_flags, ac);
	if (page)
		goto got_pg;

	/* Caller is not willing to reclaim, we can't balance anything */
	if (!can_direct_reclaim)
		goto nopage;

	/* Try direct reclaim and then allocating */
	page = __alloc_pages_direct_reclaim(gfp_mask, order, alloc_flags, ac,
							&did_some_progress);
	if (page)
		goto got_pg;

	/* Try direct compaction and then allocating */
	page = __alloc_pages_direct_compact(gfp_mask, order, alloc_flags, ac,
					compact_priority, &compact_result);
	if (page)
		goto got_pg;

	/* Do not loop if specifically requested */
	if (gfp_mask & __GFP_NORETRY)
		goto nopage;

	/*
	 * It doesn't make any sense to retry for the compaction if the order-0
	 * reclaim is not able to make any progress because the current
	 * implementation of the compaction depends on the sufficient amount
	 * of free memory (see __compaction_suitable)
	 */
	if (did_some_progress > 0 &&
			should_compact_retry(ac, order, alloc_flags,
				compact_result, &compact_priority,
				&compaction_retries))
		goto retry;

	/*
	 * It's possible we raced with cpuset update so the OOM would be
	 * premature (see below the nopage: label for full explanation).
	 */
	if (read_mems_allowed_retry(cpuset_mems_cookie))
		goto retry_cpuset;

	/* Reclaim has failed us, start killing things */
	page = __alloc_pages_may_oom(gfp_mask, order, ac, &did_some_progress);
	if (page)
		goto got_pg;

	/* Avoid allocations with no watermarks from looping endlessly */
	if (test_thread_flag(TIF_MEMDIE) &&
	    (alloc_flags == ALLOC_NO_WATERMARKS ||
	     (gfp_mask & __GFP_NOMEMALLOC)))
		goto nopage;

	/* Retry as long as the OOM killer is making progress */
	if (did_some_progress) {
		no_progress_loops = 0;
		goto retry;
	}

static inline struct page *
__alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
						struct alloc_context *ac)
{
	...
retry:
	/* Ensure kswapd doesn't accidentally go to sleep as long as we loop */
	if (gfp_mask & __GFP_KSWAPD_RECLAIM)
		wake_all_kswapds(order, ac);

	if (gfp_pfmemalloc_allowed(gfp_mask))
		alloc_flags = ALLOC_NO_WATERMARKS;

	/*
	 * Reset the zonelist iterators if memory policies can be ignored.
	 * These allocations are high priority and system rather than user
	 * orientated.
	 */
	if (!(alloc_flags & ALLOC_CPUSET) || (alloc_flags & ALLOC_NO_WATERMARKS)) {
		ac->zonelist = node_zonelist(numa_node_id(), gfp_mask);
		ac->preferred_zoneref = first_zones_zonelist(ac->zonelist,
					ac->high_zoneidx, ac->nodemask);
	}

	/* Attempt with potentially adjusted zonelist and alloc_flags */
	page = get_page_from_freelist(gfp_mask, order, alloc_flags, ac);
	if (page)
		goto got_pg;

	/* Caller is not willing to reclaim, we can't balance anything */
	if (!can_direct_reclaim)
		goto nopage;

	/* Make sure we know about allocations which stall for too long */
	if (time_after(jiffies, alloc_start + stall_timeout)) {
		warn_alloc(gfp_mask & ~__GFP_NOWARN, ac->nodemask,
			"page allocation stalls for %ums, order:%u",
			jiffies_to_msecs(jiffies-alloc_start), order);
		stall_timeout += 10 * HZ;
	}

	/* Avoid recursion of direct reclaim */
	if (current->flags & PF_MEMALLOC)
		goto nopage;

	/* Try direct reclaim and then allocating */
	page = __alloc_pages_direct_reclaim(gfp_mask, order, alloc_flags, ac,
							&did_some_progress);
	if (page)
		goto got_pg;

	/* Try direct compaction and then allocating */
	page = __alloc_pages_direct_compact(gfp_mask, order, alloc_flags, ac,
					compact_priority, &compact_result);
	if (page)
		goto got_pg;

	/* Do not loop if specifically requested */
	if (gfp_mask & __GFP_NORETRY)
		goto nopage;

	/*
	 * Do not retry costly high order allocations unless they are
	 * __GFP_REPEAT
	 */
	if (costly_order && !(gfp_mask & __GFP_REPEAT))
		goto nopage;

	if (should_reclaim_retry(gfp_mask, order, ac, alloc_flags,
				 did_some_progress > 0, &no_progress_loops))
		goto retry;

	/*
	 * It doesn't make any sense to retry for the compaction if the order-0
	 * reclaim is not able to make any progress because the current
	 * implementation of the compaction depends on the sufficient amount
	 * of free memory (see __compaction_suitable)
	 */
	if (did_some_progress > 0 &&
			should_compact_retry(ac, order, alloc_flags,
				compact_result, &compact_priority,
				&compaction_retries))
		goto retry;

	/*
	 * It's possible we raced with cpuset update so the OOM would be
	 * premature (see below the nopage: label for full explanation).
	 */
	if (read_mems_allowed_retry(cpuset_mems_cookie))
		goto retry_cpuset;

	/* Reclaim has failed us, start killing things */
	page = __alloc_pages_may_oom(gfp_mask, order, ac, &did_some_progress);
	if (page)
		goto got_pg;

	/* Avoid allocations with no watermarks from looping endlessly */
	if (test_thread_flag(TIF_MEMDIE) &&
	    (alloc_flags == ALLOC_NO_WATERMARKS ||
	     (gfp_mask & __GFP_NOMEMALLOC)))
		goto nopage;

	/* Retry as long as the OOM killer is making progress */
	if (did_some_progress) {
		no_progress_loops = 0;
		goto retry;
	}
	...
}