From: Mel Gorman <mgorman@techsingularity.net>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: NeilBrown <neilb@suse.de>, Theodore Ts'o <tytso@mit.edu>,
Andreas Dilger <adilger.kernel@dilger.ca>,
"Darrick J . Wong" <djwong@kernel.org>,
Matthew Wilcox <willy@infradead.org>,
Michal Hocko <mhocko@suse.com>,
Dave Chinner <david@fromorbit.com>,
Rik van Riel <riel@surriel.com>, Vlastimil Babka <vbabka@suse.cz>,
Johannes Weiner <hannes@cmpxchg.org>,
Jonathan Corbet <corbet@lwn.net>, Linux-MM <linux-mm@kvack.org>,
Linux-fsdevel <linux-fsdevel@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
Mel Gorman <mgorman@techsingularity.net>
Subject: [PATCH 6/8] mm/vmscan: Centralise timeout values for reclaim_throttle
Date: Fri, 22 Oct 2021 15:46:49 +0100 [thread overview]
Message-ID: <20211022144651.19914-7-mgorman@techsingularity.net> (raw)
In-Reply-To: <20211022144651.19914-1-mgorman@techsingularity.net>
Neil Brown raised concerns about callers of reclaim_throttle specifying
a timeout value. The original timeout values to congestion_wait() were
probably pulled out of thin air or copy&pasted from somewhere else.
This patch centralises the timeout values and selects a timeout based
on the reason for reclaim throttling. These figures are also pulled
out of the same thin air but better values may be derived
Running a workload that is throttling for inappropriate periods
and tracing mm_vmscan_throttled can be used to pick a more appropriate
value. Excessive throttling would pick a lower timeout where as
excessive CPU usage in reclaim context would select a larger timeout.
Ideally a large value would always be used and the wakeups would
occur before a timeout but that requires careful testing.
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
---
mm/compaction.c | 2 +-
mm/internal.h | 3 +--
mm/page-writeback.c | 2 +-
mm/vmscan.c | 50 +++++++++++++++++++++++++++++++++------------
4 files changed, 40 insertions(+), 17 deletions(-)
diff --git a/mm/compaction.c b/mm/compaction.c
index 7359093d8ac0..151b04c4dab3 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -828,7 +828,7 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
if (cc->mode == MIGRATE_ASYNC)
return -EAGAIN;
- reclaim_throttle(pgdat, VMSCAN_THROTTLE_ISOLATED, HZ/10);
+ reclaim_throttle(pgdat, VMSCAN_THROTTLE_ISOLATED);
if (fatal_signal_pending(current))
return -EINTR;
diff --git a/mm/internal.h b/mm/internal.h
index c72d3383ef34..383d9b7e7991 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -129,8 +129,7 @@ extern unsigned long highest_memmap_pfn;
*/
extern int isolate_lru_page(struct page *page);
extern void putback_lru_page(struct page *page);
-extern void reclaim_throttle(pg_data_t *pgdat, enum vmscan_throttle_state reason,
- long timeout);
+extern void reclaim_throttle(pg_data_t *pgdat, enum vmscan_throttle_state reason);
/*
* in mm/rmap.c:
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index f34f54fcd5b4..4b01a6872f9e 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2374,7 +2374,7 @@ int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
* guess as any.
*/
reclaim_throttle(NODE_DATA(numa_node_id()),
- VMSCAN_THROTTLE_WRITEBACK, HZ/50);
+ VMSCAN_THROTTLE_WRITEBACK);
}
/*
* Usually few pages are written by now from those we've just submitted
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 0450f6867d61..66da45084af4 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1006,12 +1006,10 @@ static void handle_write_error(struct address_space *mapping,
unlock_page(page);
}
-void reclaim_throttle(pg_data_t *pgdat, enum vmscan_throttle_state reason,
- long timeout)
+void reclaim_throttle(pg_data_t *pgdat, enum vmscan_throttle_state reason)
{
wait_queue_head_t *wqh = &pgdat->reclaim_wait[reason];
- long ret;
- bool acct_writeback = (reason == VMSCAN_THROTTLE_WRITEBACK);
+ long timeout, ret;
DEFINE_WAIT(wait);
/*
@@ -1023,17 +1021,43 @@ void reclaim_throttle(pg_data_t *pgdat, enum vmscan_throttle_state reason,
current->flags & (PF_IO_WORKER|PF_KTHREAD))
return;
- if (acct_writeback &&
- atomic_inc_return(&pgdat->nr_writeback_throttled) == 1) {
- WRITE_ONCE(pgdat->nr_reclaim_start,
- node_page_state(pgdat, NR_THROTTLED_WRITTEN));
+ /*
+ * These figures are pulled out of thin air.
+ * VMSCAN_THROTTLE_ISOLATED is a transient condition based on too many
+ * parallel reclaimers which is a short-lived event so the timeout is
+ * short. Failing to make progress or waiting on writeback are
+ * potentially long-lived events so use a longer timeout. This is shaky
+ * logic as a failure to make progress could be due to anything from
+ * writeback to a slow device to excessive references pages at the tail
+ * of the inactive LRU.
+ */
+ switch(reason) {
+ case VMSCAN_THROTTLE_WRITEBACK:
+ timeout = HZ/10;
+
+ if (atomic_inc_return(&pgdat->nr_writeback_throttled) == 1) {
+ WRITE_ONCE(pgdat->nr_reclaim_start,
+ node_page_state(pgdat, NR_THROTTLED_WRITTEN));
+ }
+
+ break;
+ case VMSCAN_THROTTLE_NOPROGRESS:
+ timeout = HZ/10;
+ break;
+ case VMSCAN_THROTTLE_ISOLATED:
+ timeout = HZ/50;
+ break;
+ default:
+ WARN_ON_ONCE(1);
+ timeout = HZ;
+ break;
}
prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
ret = schedule_timeout(timeout);
finish_wait(wqh, &wait);
- if (acct_writeback)
+ if (reason == VMSCAN_THROTTLE_WRITEBACK)
atomic_dec(&pgdat->nr_writeback_throttled);
trace_mm_vmscan_throttled(pgdat->node_id, jiffies_to_usecs(timeout),
@@ -2319,7 +2343,7 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
/* wait a bit for the reclaimer. */
stalled = true;
- reclaim_throttle(pgdat, VMSCAN_THROTTLE_ISOLATED, HZ/10);
+ reclaim_throttle(pgdat, VMSCAN_THROTTLE_ISOLATED);
/* We are about to die and free our memory. Return now. */
if (fatal_signal_pending(current))
@@ -3251,7 +3275,7 @@ static void shrink_node(pg_data_t *pgdat, struct scan_control *sc)
* until some pages complete writeback.
*/
if (sc->nr.immediate)
- reclaim_throttle(pgdat, VMSCAN_THROTTLE_WRITEBACK, HZ/10);
+ reclaim_throttle(pgdat, VMSCAN_THROTTLE_WRITEBACK);
}
/*
@@ -3275,7 +3299,7 @@ static void shrink_node(pg_data_t *pgdat, struct scan_control *sc)
if (!current_is_kswapd() && current_may_throttle() &&
!sc->hibernation_mode &&
test_bit(LRUVEC_CONGESTED, &target_lruvec->flags))
- reclaim_throttle(pgdat, VMSCAN_THROTTLE_WRITEBACK, HZ/10);
+ reclaim_throttle(pgdat, VMSCAN_THROTTLE_WRITEBACK);
if (should_continue_reclaim(pgdat, sc->nr_reclaimed - nr_reclaimed,
sc))
@@ -3347,7 +3371,7 @@ static void consider_reclaim_throttle(pg_data_t *pgdat, struct scan_control *sc)
/* Throttle if making no progress at high prioities. */
if (sc->priority < DEF_PRIORITY - 2)
- reclaim_throttle(pgdat, VMSCAN_THROTTLE_NOPROGRESS, HZ/10);
+ reclaim_throttle(pgdat, VMSCAN_THROTTLE_NOPROGRESS);
}
/*
--
2.31.1
next prev parent reply other threads:[~2021-10-22 14:48 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-22 14:46 [PATCH v5 0/8] Remove dependency on congestion_wait in mm/ Mel Gorman
2021-10-22 14:46 ` [PATCH 1/8] mm/vmscan: Throttle reclaim until some writeback completes if congested Mel Gorman
2021-10-22 14:46 ` [PATCH 2/8] mm/vmscan: Throttle reclaim and compaction when too may pages are isolated Mel Gorman
2021-10-22 14:46 ` [PATCH 3/8] mm/vmscan: Throttle reclaim when no progress is being made Mel Gorman
2021-11-24 1:19 ` Darrick J. Wong
2021-11-24 1:49 ` Darrick J. Wong
2021-11-24 14:35 ` Mel Gorman
2021-11-24 18:02 ` Darrick J. Wong
2021-11-24 10:32 ` Mel Gorman
2021-11-24 10:43 ` Vlastimil Babka
2021-11-24 10:53 ` Mel Gorman
2021-11-24 17:24 ` Mike Galbraith
2021-10-22 14:46 ` [PATCH 4/8] mm/writeback: Throttle based on page writeback instead of congestion Mel Gorman
2021-10-22 14:46 ` [PATCH 5/8] mm/page_alloc: Remove the throttling logic from the page allocator Mel Gorman
2021-10-25 10:07 ` Vlastimil Babka
2021-10-22 14:46 ` Mel Gorman [this message]
2021-10-22 14:46 ` [PATCH 7/8] mm/vmscan: Increase the timeout if page reclaim is not making progress Mel Gorman
2021-10-22 14:46 ` [PATCH 8/8] mm/vmscan: Delay waking of tasks throttled on NOPROGRESS Mel Gorman
-- strict thread matches above, loose matches on Subject: below --
2021-10-19 9:01 [PATCH v4 0/8] Remove dependency on congestion_wait in mm/ Mel Gorman
2021-10-19 9:01 ` [PATCH 6/8] mm/vmscan: Centralise timeout values for reclaim_throttle Mel Gorman
2021-10-22 1:06 ` NeilBrown
2021-10-22 8:12 ` Mel Gorman
2021-10-08 13:53 [PATCH v3 0/8] Remove dependency on congestion_wait in mm/ Mel Gorman
2021-10-08 13:53 ` [PATCH 6/8] mm/vmscan: Centralise timeout values for reclaim_throttle Mel Gorman
2021-10-14 15:38 ` Vlastimil Babka
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