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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 58bea73b06fc6f759b4f3ef2ace11a07987f3714..3a89cebdd80f756a0d5d7a553d64b463e0ec1365 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -121,6 +121,10 @@ config ZEN_INTERACTIVE
Default scheduler.........: mq-deadline -> bfq
+ --- Virtual Memory Subsystem ---------------------------
+
+ Background-reclaim hugepages...: no -> yes
+
config BROKEN
bool
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 910a138e9859e9a6c02e7bf234c5431c8e3cebb5..9e4760e2ae587de6f443ffb628dfc2a4d0671b6b 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -58,7 +58,11 @@ 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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