The patch titled
Subject: mm: avoid waking kswapd for THP allocations when compaction is deferred or contended
has been added to the -mm tree. Its filename is
mm-avoid-waking-kswapd-for-thp-allocations-when-compaction-is-deferred-or-contended.patch
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------------------------------------------------------
From: Mel Gorman <mgorman@xxxxxxx>
Subject: mm: avoid waking kswapd for THP allocations when compaction is deferred or contended
With "mm: vmscan: scale number of pages reclaimed by reclaim/compaction
based on failures" reverted, Zdenek Kabelac reported the following
Hmm, so it's just took longer to hit the problem and observe
kswapd0 spinning on my CPU again - it's not as endless like before -
but still it easily eats minutes - it helps to turn off Firefox
or TB (memory hungry apps) so kswapd0 stops soon - and restart
those apps again. (And I still have like >1GB of cached memory)
kswapd0 R running task 0 30 2 0x00000000
ffff8801331efae8 0000000000000082 0000000000000018 0000000000000246
ffff880135b9a340 ffff8801331effd8 ffff8801331effd8 ffff8801331effd8
ffff880055dfa340 ffff880135b9a340 00000000331efad8 ffff8801331ee000
Call Trace:
[<ffffffff81555bf2>] preempt_schedule+0x42/0x60
[<ffffffff81557a95>] _raw_spin_unlock+0x55/0x60
[<ffffffff81192971>] put_super+0x31/0x40
[<ffffffff81192a42>] drop_super+0x22/0x30
[<ffffffff81193b89>] prune_super+0x149/0x1b0
[<ffffffff81141e2a>] shrink_slab+0xba/0x510
The sysrq+m indicates the system has no swap so it'll never reclaim
anonymous pages as part of reclaim/compaction. That is one part of the
problem but not the root cause as file-backed pages could also be
reclaimed.
The likely underlying problem is that kswapd is woken up or kept awake for
each THP allocation request in the page allocator slow path.
If compaction fails for the requesting process then compaction will be
deferred for a time and direct reclaim is avoided. However, if there are
a storm of THP requests that are simply rejected, it will still be the the
case that kswapd is awake for a prolonged period of time as
pgdat->kswapd_max_order is updated each time. This is noticed by the main
kswapd() loop and it will not call kswapd_try_to_sleep(). Instead it will
loopp, shrinking a small number of pages and calling shrink_slab() on each
iteration.
This patch defers when kswapd gets woken up for THP allocations. For !THP
allocations, kswapd is always woken up. For THP allocations, kswapd is
woken up iff the process is willing to enter into direct
reclaim/compaction.
Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
Cc: Zdenek Kabelac <zkabelac@xxxxxxxxxx>
Cc: Seth Jennings <sjenning@xxxxxxxxxxxxxxxxxx>
Cc: Jiri Slaby <jirislaby@xxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Robert Jennings <rcj@xxxxxxxxxxxxxxxxxx>
Cc: Valdis Kletnieks <Valdis.Kletnieks@xxxxxx>
Cc: Glauber Costa <glommer@xxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page_alloc.c | 37 +++++++++++++++++++++++++++----------
1 file changed, 27 insertions(+), 10 deletions(-)
diff -puN mm/page_alloc.c~mm-avoid-waking-kswapd-for-thp-allocations-when-compaction-is-deferred-or-contended mm/page_alloc.c
--- a/mm/page_alloc.c~mm-avoid-waking-kswapd-for-thp-allocations-when-compaction-is-deferred-or-contended
+++ a/mm/page_alloc.c
@@ -2378,6 +2378,15 @@ bool gfp_pfmemalloc_allowed(gfp_t gfp_ma
return !!(gfp_to_alloc_flags(gfp_mask) & ALLOC_NO_WATERMARKS);
}
+/* Returns true if the allocation is likely for THP */
+static bool is_thp_alloc(gfp_t gfp_mask, unsigned int order)
+{
+ if (order == pageblock_order &&
+ (gfp_mask & (__GFP_MOVABLE|__GFP_REPEAT)) == __GFP_MOVABLE)
+ return true;
+ return false;
+}
+
static inline struct page *
__alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
struct zonelist *zonelist, enum zone_type high_zoneidx,
@@ -2416,7 +2425,9 @@ __alloc_pages_slowpath(gfp_t gfp_mask, u
goto nopage;
restart:
- wake_all_kswapd(order, zonelist, high_zoneidx,
+ /* The decision whether to wake kswapd for THP is made later */
+ if (!is_thp_alloc(gfp_mask, order))
+ wake_all_kswapd(order, zonelist, high_zoneidx,
zone_idx(preferred_zone));
/*
@@ -2487,15 +2498,21 @@ rebalance:
goto got_pg;
sync_migration = true;
- /*
- * If compaction is deferred for high-order allocations, it is because
- * sync compaction recently failed. In this is the case and the caller
- * requested a movable allocation that does not heavily disrupt the
- * system then fail the allocation instead of entering direct reclaim.
- */
- if ((deferred_compaction || contended_compaction) &&
- (gfp_mask & (__GFP_MOVABLE|__GFP_REPEAT)) == __GFP_MOVABLE)
- goto nopage;
+ if (is_thp_alloc(gfp_mask, order)) {
+ /*
+ * If compaction is deferred for high-order allocations, it is
+ * because sync compaction recently failed. In this is the case
+ * and the caller requested a movable allocation that does not
+ * heavily disrupt the system then fail the allocation instead
+ * of entering direct reclaim.
+ */
+ if (deferred_compaction || contended_compaction)
+ goto nopage;
+
+ /* If process is willing to reclaim/compact then wake kswapd */
+ wake_all_kswapd(order, zonelist, high_zoneidx,
+ zone_idx(preferred_zone));
+ }
/* Try direct reclaim and then allocating */
page = __alloc_pages_direct_reclaim(gfp_mask, order,
_
Patches currently in -mm which might be from mgorman@xxxxxxx are
origin.patch
mm-compaction-fix-return-value-of-capture_free_page.patch
revert-revert-mm-remove-__gfp_no_kswapd.patch
mm-avoid-waking-kswapd-for-thp-allocations-when-compaction-is-deferred-or-contended.patch
linux-next.patch
memory_hotplug-fix-possible-incorrect-node_states.patch
slub-hotplug-ignore-unrelated-nodes-hot-adding-and-hot-removing.patch
mm-add-comment-on-storage-key-dirty-bit-semantics.patch
mm-refactor-reinsert-of-swap_info-in-sys_swapoff.patch
mm-do-not-call-frontswap_init-during-swapoff.patch
mm-memmap_init_zone-performance-improvement.patch
mm-allocate-kernel-pages-to-the-right-memcg.patch
mm-memory-hotplug-dynamic-configure-movable-memory-and-portion-memory.patch
memory_hotplug-handle-empty-zone-when-online_movable-online_kernel.patch
memory_hotplug-ensure-every-online-node-has-normal-memory.patch
mm-compaction-fix-compiler-warning.patch
mm-add-a-reminder-comment-for-__gfp_bits_shift.patch
numa-add-config_movable_node-for-movable-dedicated-node.patch
numa-add-config_movable_node-for-movable-dedicated-node-fix.patch
memory_hotplug-allow-online-offline-memory-to-result-movable-node.patch
mm-introduce-new-field-managed_pages-to-struct-zone.patch
mm-provide-more-accurate-estimation-of-pages-occupied-by-memmap.patch
mm-provide-more-accurate-estimation-of-pages-occupied-by-memmap-fix.patch
mm-avoid-waking-kswapd-for-thp-allocations-when-compaction-is-deferred-or-contended-fix.patch
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