mm: update_lru_size warn and reset bad lru_size (ca707239) · Commits · 戴 / test

Though debug kernels have a VM_BUG_ON to help protect from misaccounting lru_size, non-debug kernels are liable to wrap it around: and then the vast unsigned long size draws page reclaim into a loop of repeatedly doing nothing on an empty list, without even a cond_resched(). That soft lockup looks confusingly like an over-busy reclaim scenario, with lots of contention on the lru_lock in shrink_inactive_list(): yet has a totally different origin. Help differentiate with a custom warning in mem_cgroup_update_lru_size(), even in non-debug kernels; and reset the size to avoid the lockup. But the particular bug which suggested this change was mine alone, and since fixed. Make it a WARN_ONCE: the first occurrence is the most informative, a flurry may follow, yet even when rate-limited little more is learnt. Signed-off-by:

Hugh Dickins <hughd@google.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Andres Lagar-Cavilla <andreslc@google.com> Cc: Yang Shi <yang.shi@linaro.org> Cc: Ning Qu <quning@gmail.com> Cc: Mel Gorman <mgorman@techsingularity.net> Cc: Andres Lagar-Cavilla <andreslc@google.com> Cc: Konstantin Khlebnikov <koct9i@gmail.com> Cc: Michal Hocko <mhocko@kernel.org> Cc: Johannes Weiner <hannes@cmpxchg.org> Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

include/linux/mm_inline.h

+1 −1

Original line number	Diff line number	Diff line
		@@ -35,8 +35,8 @@ static __always_inline void del_page_from_lru_list(struct page *page,
		struct lruvec *lruvec, enum lru_list lru)
		{
		int nr_pages = hpage_nr_pages(page);
		mem_cgroup_update_lru_size(lruvec, lru, -nr_pages);
		list_del(&page->lru);
		mem_cgroup_update_lru_size(lruvec, lru, -nr_pages);
		__mod_zone_page_state(lruvec_zone(lruvec), NR_LRU_BASE + lru, -nr_pages);
		}

mm/memcontrol.c

+20 −4

Original line number	Diff line number	Diff line
		@@ -1023,22 +1023,38 @@ out:
		* @lru: index of lru list the page is sitting on
		* @nr_pages: positive when adding or negative when removing
		*
		* This function must be called when a page is added to or removed from an
		* lru list.
		* This function must be called under lru_lock, just before a page is added
		* to or just after a page is removed from an lru list (that ordering being
		* so as to allow it to check that lru_size 0 is consistent with list_empty).
		*/
		void mem_cgroup_update_lru_size(struct lruvec *lruvec, enum lru_list lru,
		int nr_pages)
		{
		struct mem_cgroup_per_zone *mz;
		unsigned long *lru_size;
		long size;
		bool empty;

		if (mem_cgroup_disabled())
		return;

		mz = container_of(lruvec, struct mem_cgroup_per_zone, lruvec);
		lru_size = mz->lru_size + lru;
		empty = list_empty(lruvec->lists + lru);

		if (nr_pages < 0)
		*lru_size += nr_pages;

		size = *lru_size;
		if (WARN_ONCE(size < 0 \|\| empty != !size,
		"%s(%p, %d, %d): lru_size %ld but %sempty\n",
		__func__, lruvec, lru, nr_pages, size, empty ? "" : "not ")) {
		VM_BUG_ON(1);
		*lru_size = 0;
		}

		if (nr_pages > 0)
		*lru_size += nr_pages;
		VM_BUG_ON((long)(*lru_size) < 0);
		}

		bool task_in_mem_cgroup(struct task_struct task, struct mem_cgroup memcg)

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