mm: don't avoid high-priority reclaim on memcg limit reclaim (688035f7) · Commits · 戴 / test

Commit ("memcg: fix get_scan_count() for small targets") sought to avoid high reclaim priorities for memcg by forcing it to scan a minimum amount of pages when lru_pages >> priority yielded nothing. This was done at a time when reclaim decisions like dirty throttling were tied to the priority level. Nowadays, the only meaningful thing still tied to priority dropping below DEF_PRIORITY - 2 is gating whether laptop_mode=1 is generally allowed to write. But that is from an era where direct reclaim was still allowed to call ->writepage, and kswapd nowadays avoids writes until it's scanned every clean page in the system. Potential changes to how quick sc->may_writepage could trigger are of little concern. Remove the force_scan stuff, as well as the ugly multi-pass target calculation that it necessitated. Link: http://lkml.kernel.org/r/20170228214007.5621-7-hannes@cmpxchg.org Signed-off-by:

Johannes Weiner <hannes@cmpxchg.org> Acked-by:

Hillf Danton <hillf.zj@alibaba-inc.com> Acked-by:

Michal Hocko <mhocko@suse.com> Cc: Jia He <hejianet@gmail.com> Cc: Mel Gorman <mgorman@suse.de> Signed-off-by:

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

Linus Torvalds <torvalds@linux-foundation.org>

mm/vmscan.c

+37 −57

Original line number	Diff line number	Diff line
		@@ -2123,21 +2123,8 @@ static void get_scan_count(struct lruvec lruvec, struct mem_cgroup memcg,
		unsigned long anon_prio, file_prio;
		enum scan_balance scan_balance;
		unsigned long anon, file;
		bool force_scan = false;
		unsigned long ap, fp;
		enum lru_list lru;
		bool some_scanned;
		int pass;

		/*
		* If the zone or memcg is small, nr[l] can be 0. When
		* reclaiming for a memcg, a priority drop can cause high
		* latencies, so it's better to scan a minimum amount. When a
		* cgroup has already been deleted, scrape out the remaining
		* cache forcefully to get rid of the lingering state.
		*/
		if (!global_reclaim(sc) \|\| !mem_cgroup_online(memcg))
		force_scan = true;

		/* If we have no swap space, do not bother scanning anon pages. */
		if (!sc->may_swap \|\| mem_cgroup_get_nr_swap_pages(memcg) <= 0) {
		@@ -2268,9 +2255,6 @@ static void get_scan_count(struct lruvec lruvec, struct mem_cgroup memcg,
		fraction[1] = fp;
		denominator = ap + fp + 1;
		out:
		some_scanned = false;
		/* Only use force_scan on second pass. */
		for (pass = 0; !some_scanned && pass < 2; pass++) {
		*lru_pages = 0;
		for_each_evictable_lru(lru) {
		int file = is_file_lru(lru);
		@@ -2279,8 +2263,11 @@ out:

		size = lruvec_lru_size(lruvec, lru, sc->reclaim_idx);
		scan = size >> sc->priority;

		if (!scan && pass && force_scan)
		/*
		* If the cgroup's already been deleted, make sure to
		* scrape out the remaining cache.
		*/
		if (!scan && !mem_cgroup_online(memcg))
		scan = min(size, SWAP_CLUSTER_MAX);

		switch (scan_balance) {
		@@ -2310,13 +2297,6 @@ out:

		*lru_pages += size;
		nr[lru] = scan;

		/*
		* Skip the second pass and don't force_scan,
		* if we found something to scan.
		*/
		some_scanned \|= !!scan;
		}
		}
		}

Admin message