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Message-Id: <20191022144803.302233-6-hannes@cmpxchg.org>
Date: Tue, 22 Oct 2019 10:48:00 -0400
From: Johannes Weiner <hannes@...xchg.org>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Michal Hocko <mhocko@...e.com>, linux-mm@...ck.org,
cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
kernel-team@...com
Subject: [PATCH 5/8] mm: vmscan: replace shrink_node() loop with a retry jump
Most of the function body is inside a loop, which imposes an
additional indentation and scoping level that makes the code a bit
hard to follow and modify.
The looping only happens in case of reclaim-compaction, which isn't
the common case. So rather than adding yet another function level to
the reclaim path and have every reclaim invocation go through a level
that only exists for one specific cornercase, use a retry goto.
Signed-off-by: Johannes Weiner <hannes@...xchg.org>
---
mm/vmscan.c | 231 ++++++++++++++++++++++++++--------------------------
1 file changed, 115 insertions(+), 116 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 302dad112f75..235d1fc72311 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2729,144 +2729,143 @@ static bool pgdat_memcg_congested(pg_data_t *pgdat, struct mem_cgroup *memcg)
static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc)
{
struct reclaim_state *reclaim_state = current->reclaim_state;
+ struct mem_cgroup *root = sc->target_mem_cgroup;
unsigned long nr_reclaimed, nr_scanned;
bool reclaimable = false;
+ struct mem_cgroup *memcg;
+again:
+ memset(&sc->nr, 0, sizeof(sc->nr));
- do {
- struct mem_cgroup *root = sc->target_mem_cgroup;
- struct mem_cgroup *memcg;
-
- memset(&sc->nr, 0, sizeof(sc->nr));
-
- nr_reclaimed = sc->nr_reclaimed;
- nr_scanned = sc->nr_scanned;
+ nr_reclaimed = sc->nr_reclaimed;
+ nr_scanned = sc->nr_scanned;
- memcg = mem_cgroup_iter(root, NULL, NULL);
- do {
- unsigned long reclaimed;
- unsigned long scanned;
+ memcg = mem_cgroup_iter(root, NULL, NULL);
+ do {
+ unsigned long reclaimed;
+ unsigned long scanned;
- switch (mem_cgroup_protected(root, memcg)) {
- case MEMCG_PROT_MIN:
- /*
- * Hard protection.
- * If there is no reclaimable memory, OOM.
- */
+ switch (mem_cgroup_protected(root, memcg)) {
+ case MEMCG_PROT_MIN:
+ /*
+ * Hard protection.
+ * If there is no reclaimable memory, OOM.
+ */
+ continue;
+ case MEMCG_PROT_LOW:
+ /*
+ * Soft protection.
+ * Respect the protection only as long as
+ * there is an unprotected supply
+ * of reclaimable memory from other cgroups.
+ */
+ if (!sc->memcg_low_reclaim) {
+ sc->memcg_low_skipped = 1;
continue;
- case MEMCG_PROT_LOW:
- /*
- * Soft protection.
- * Respect the protection only as long as
- * there is an unprotected supply
- * of reclaimable memory from other cgroups.
- */
- if (!sc->memcg_low_reclaim) {
- sc->memcg_low_skipped = 1;
- continue;
- }
- memcg_memory_event(memcg, MEMCG_LOW);
- break;
- case MEMCG_PROT_NONE:
- /*
- * All protection thresholds breached. We may
- * still choose to vary the scan pressure
- * applied based on by how much the cgroup in
- * question has exceeded its protection
- * thresholds (see get_scan_count).
- */
- break;
}
+ memcg_memory_event(memcg, MEMCG_LOW);
+ break;
+ case MEMCG_PROT_NONE:
+ /*
+ * All protection thresholds breached. We may
+ * still choose to vary the scan pressure
+ * applied based on by how much the cgroup in
+ * question has exceeded its protection
+ * thresholds (see get_scan_count).
+ */
+ break;
+ }
- reclaimed = sc->nr_reclaimed;
- scanned = sc->nr_scanned;
- shrink_node_memcg(pgdat, memcg, sc);
-
- shrink_slab(sc->gfp_mask, pgdat->node_id, memcg,
- sc->priority);
-
- /* Record the group's reclaim efficiency */
- vmpressure(sc->gfp_mask, memcg, false,
- sc->nr_scanned - scanned,
- sc->nr_reclaimed - reclaimed);
-
- } while ((memcg = mem_cgroup_iter(root, memcg, NULL)));
+ reclaimed = sc->nr_reclaimed;
+ scanned = sc->nr_scanned;
+ shrink_node_memcg(pgdat, memcg, sc);
- if (reclaim_state) {
- sc->nr_reclaimed += reclaim_state->reclaimed_slab;
- reclaim_state->reclaimed_slab = 0;
- }
+ shrink_slab(sc->gfp_mask, pgdat->node_id, memcg,
+ sc->priority);
- /* Record the subtree's reclaim efficiency */
- vmpressure(sc->gfp_mask, sc->target_mem_cgroup, true,
- sc->nr_scanned - nr_scanned,
- sc->nr_reclaimed - nr_reclaimed);
+ /* Record the group's reclaim efficiency */
+ vmpressure(sc->gfp_mask, memcg, false,
+ sc->nr_scanned - scanned,
+ sc->nr_reclaimed - reclaimed);
- if (sc->nr_reclaimed - nr_reclaimed)
- reclaimable = true;
+ } while ((memcg = mem_cgroup_iter(root, memcg, NULL)));
- if (current_is_kswapd()) {
- /*
- * If reclaim is isolating dirty pages under writeback,
- * it implies that the long-lived page allocation rate
- * is exceeding the page laundering rate. Either the
- * global limits are not being effective at throttling
- * processes due to the page distribution throughout
- * zones or there is heavy usage of a slow backing
- * device. The only option is to throttle from reclaim
- * context which is not ideal as there is no guarantee
- * the dirtying process is throttled in the same way
- * balance_dirty_pages() manages.
- *
- * Once a node is flagged PGDAT_WRITEBACK, kswapd will
- * count the number of pages under pages flagged for
- * immediate reclaim and stall if any are encountered
- * in the nr_immediate check below.
- */
- if (sc->nr.writeback && sc->nr.writeback == sc->nr.taken)
- set_bit(PGDAT_WRITEBACK, &pgdat->flags);
+ if (reclaim_state) {
+ sc->nr_reclaimed += reclaim_state->reclaimed_slab;
+ reclaim_state->reclaimed_slab = 0;
+ }
- /*
- * Tag a node as congested if all the dirty pages
- * scanned were backed by a congested BDI and
- * wait_iff_congested will stall.
- */
- if (sc->nr.dirty && sc->nr.dirty == sc->nr.congested)
- set_bit(PGDAT_CONGESTED, &pgdat->flags);
+ /* Record the subtree's reclaim efficiency */
+ vmpressure(sc->gfp_mask, sc->target_mem_cgroup, true,
+ sc->nr_scanned - nr_scanned,
+ sc->nr_reclaimed - nr_reclaimed);
- /* Allow kswapd to start writing pages during reclaim.*/
- if (sc->nr.unqueued_dirty == sc->nr.file_taken)
- set_bit(PGDAT_DIRTY, &pgdat->flags);
+ if (sc->nr_reclaimed - nr_reclaimed)
+ reclaimable = true;
- /*
- * If kswapd scans pages marked marked for immediate
- * reclaim and under writeback (nr_immediate), it
- * implies that pages are cycling through the LRU
- * faster than they are written so also forcibly stall.
- */
- if (sc->nr.immediate)
- congestion_wait(BLK_RW_ASYNC, HZ/10);
- }
+ if (current_is_kswapd()) {
+ /*
+ * If reclaim is isolating dirty pages under writeback,
+ * it implies that the long-lived page allocation rate
+ * is exceeding the page laundering rate. Either the
+ * global limits are not being effective at throttling
+ * processes due to the page distribution throughout
+ * zones or there is heavy usage of a slow backing
+ * device. The only option is to throttle from reclaim
+ * context which is not ideal as there is no guarantee
+ * the dirtying process is throttled in the same way
+ * balance_dirty_pages() manages.
+ *
+ * Once a node is flagged PGDAT_WRITEBACK, kswapd will
+ * count the number of pages under pages flagged for
+ * immediate reclaim and stall if any are encountered
+ * in the nr_immediate check below.
+ */
+ if (sc->nr.writeback && sc->nr.writeback == sc->nr.taken)
+ set_bit(PGDAT_WRITEBACK, &pgdat->flags);
/*
- * Legacy memcg will stall in page writeback so avoid forcibly
- * stalling in wait_iff_congested().
+ * Tag a node as congested if all the dirty pages
+ * scanned were backed by a congested BDI and
+ * wait_iff_congested will stall.
*/
- if (cgroup_reclaim(sc) && writeback_throttling_sane(sc) &&
- sc->nr.dirty && sc->nr.dirty == sc->nr.congested)
- set_memcg_congestion(pgdat, root, true);
+ if (sc->nr.dirty && sc->nr.dirty == sc->nr.congested)
+ set_bit(PGDAT_CONGESTED, &pgdat->flags);
+
+ /* Allow kswapd to start writing pages during reclaim.*/
+ if (sc->nr.unqueued_dirty == sc->nr.file_taken)
+ set_bit(PGDAT_DIRTY, &pgdat->flags);
/*
- * Stall direct reclaim for IO completions if underlying BDIs
- * and node is congested. Allow kswapd to continue until it
- * starts encountering unqueued dirty pages or cycling through
- * the LRU too quickly.
+ * If kswapd scans pages marked marked for immediate
+ * reclaim and under writeback (nr_immediate), it
+ * implies that pages are cycling through the LRU
+ * faster than they are written so also forcibly stall.
*/
- if (!sc->hibernation_mode && !current_is_kswapd() &&
- current_may_throttle() && pgdat_memcg_congested(pgdat, root))
- wait_iff_congested(BLK_RW_ASYNC, HZ/10);
+ if (sc->nr.immediate)
+ congestion_wait(BLK_RW_ASYNC, HZ/10);
+ }
+
+ /*
+ * Legacy memcg will stall in page writeback so avoid forcibly
+ * stalling in wait_iff_congested().
+ */
+ if (cgroup_reclaim(sc) && writeback_throttling_sane(sc) &&
+ sc->nr.dirty && sc->nr.dirty == sc->nr.congested)
+ set_memcg_congestion(pgdat, root, true);
+
+ /*
+ * Stall direct reclaim for IO completions if underlying BDIs
+ * and node is congested. Allow kswapd to continue until it
+ * starts encountering unqueued dirty pages or cycling through
+ * the LRU too quickly.
+ */
+ if (!sc->hibernation_mode && !current_is_kswapd() &&
+ current_may_throttle() && pgdat_memcg_congested(pgdat, root))
+ wait_iff_congested(BLK_RW_ASYNC, HZ/10);
- } while (should_continue_reclaim(pgdat, sc->nr_reclaimed - nr_reclaimed,
- sc));
+ if (should_continue_reclaim(pgdat, sc->nr_reclaimed - nr_reclaimed,
+ sc))
+ goto again;
/*
* Kswapd gives up on balancing particular nodes after too
--
2.23.0
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