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From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: "Jan Alexander Steffens (heftig)" <jan.steffens@gmail.com>
Date: Mon, 27 Jan 2020 18:21:09 +0100
Subject: [PATCH] ZEN: INTERACTIVE: Enable background reclaim of hugepages
Use [defer+madvise] as default khugepaged defrag strategy:
For some reason, the default strategy to respond to THP fault fallbacks
is still just madvise, meaning stall if the program wants transparent
hugepages, but don't trigger a background reclaim / compaction if THP
begins to fail allocations. This creates a snowball affect where we
still use the THP code paths, but we almost always fail once a system
has been active and busy for a while.
The option "defer" was created for interactive systems where THP can
still improve performance. If we have to fallback to a regular page due
to an allocation failure or anything else, we will trigger a background
reclaim and compaction so future THP attempts succeed and previous
attempts eventually have their smaller pages combined without stalling
running applications.
We still want madvise to stall applications that explicitely want THP,
so defer+madvise _does_ make a ton of sense. Make it the default for
interactive systems, especially if the kernel maintainer left
transparent hugepages on "always".
Reasoning and details in the original patch: https://lwn.net/Articles/711248/
---
init/Kconfig | 4 ++++
mm/huge_memory.c | 4 ++++
2 files changed, 8 insertions(+)
diff --git a/init/Kconfig b/init/Kconfig
index 3714f60c7aff537f1bd4e8aa8979a745ebe587f1..73b95d3f50300fb82220fb30dfe91bb12052f111 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -127,6 +127,10 @@ config ZEN_INTERACTIVE
Default scheduler for SQ..: mq-deadline -> bfq
Default scheduler for MQ..: none -> kyber
+ --- Virtual Memory Subsystem ---------------------------
+
+ Background-reclaim hugepages...: no -> yes
+
config BROKEN
bool
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 834f288b376909c351fc2a21d77e200f8e83a802..a78a758f9815b043dd03f03bc8028b7d483a2a9c 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -59,7 +59,11 @@ unsigned long transparent_hugepage_flags __read_mostly =
#ifdef CONFIG_TRANSPARENT_HUGEPAGE_MADVISE
(1<<TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG)|
#endif
+#ifdef CONFIG_ZEN_INTERACTIVE
+ (1<<TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_OR_MADV_FLAG)|
+#else
(1<<TRANSPARENT_HUGEPAGE_DEFRAG_REQ_MADV_FLAG)|
+#endif
(1<<TRANSPARENT_HUGEPAGE_DEFRAG_KHUGEPAGED_FLAG)|
(1<<TRANSPARENT_HUGEPAGE_USE_ZERO_PAGE_FLAG);
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