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Message-ID: <20250211004054.222931-2-npache@redhat.com>
Date: Mon, 10 Feb 2025 17:40:50 -0700
From: Nico Pache <npache@...hat.com>
To: linux-kernel@...r.kernel.org,
linux-doc@...r.kernel.org,
linux-kselftest@...r.kernel.org,
linux-mm@...ck.org
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Subject: [RFC v2 1/5] mm: defer THP insertion to khugepaged
setting /transparent_hugepages/enabled=always allows applications
to benefit from THPs without having to madvise. However, the pf handler
takes very few considerations to decide weather or not to actually use a
THP. This can lead to a lot of wasted memory. khugepaged only operates
on memory that was either allocated with enabled=always or MADV_HUGEPAGE.
Introduce the ability to set enabled=defer, which will prevent THPs from
being allocated by the page fault handler unless madvise is set,
leaving it up to khugepaged to decide which allocations will collapse to a
THP. This should allow applications to benefits from THPs, while curbing
some of the memory waste.
Signed-off-by: Nico Pache <npache@...hat.com>
---
include/linux/huge_mm.h | 15 +++++++++++++--
mm/huge_memory.c | 31 +++++++++++++++++++++++++++----
2 files changed, 40 insertions(+), 6 deletions(-)
diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
index 93e509b6c00e..fb381ca720ea 100644
--- a/include/linux/huge_mm.h
+++ b/include/linux/huge_mm.h
@@ -44,6 +44,7 @@ enum transparent_hugepage_flag {
TRANSPARENT_HUGEPAGE_UNSUPPORTED,
TRANSPARENT_HUGEPAGE_FLAG,
TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
+ TRANSPARENT_HUGEPAGE_DEFER_PF_INST_FLAG,
TRANSPARENT_HUGEPAGE_DEFRAG_DIRECT_FLAG,
TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_FLAG,
TRANSPARENT_HUGEPAGE_DEFRAG_KSWAPD_OR_MADV_FLAG,
@@ -177,6 +178,7 @@ static inline bool hugepage_global_enabled(void)
{
return transparent_hugepage_flags &
((1<<TRANSPARENT_HUGEPAGE_FLAG) |
+ (1<<TRANSPARENT_HUGEPAGE_DEFER_PF_INST_FLAG) |
(1<<TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG));
}
@@ -186,6 +188,12 @@ static inline bool hugepage_global_always(void)
(1<<TRANSPARENT_HUGEPAGE_FLAG);
}
+static inline bool hugepage_global_defer(void)
+{
+ return transparent_hugepage_flags &
+ (1<<TRANSPARENT_HUGEPAGE_DEFER_PF_INST_FLAG);
+}
+
static inline int highest_order(unsigned long orders)
{
return fls_long(orders) - 1;
@@ -282,13 +290,16 @@ unsigned long thp_vma_allowable_orders(struct vm_area_struct *vma,
unsigned long tva_flags,
unsigned long orders)
{
+ if ((tva_flags & TVA_IN_PF) && hugepage_global_defer() &&
+ !(vm_flags & VM_HUGEPAGE))
+ return 0;
+
/* Optimization to check if required orders are enabled early. */
if ((tva_flags & TVA_ENFORCE_SYSFS) && vma_is_anonymous(vma)) {
unsigned long mask = READ_ONCE(huge_anon_orders_always);
-
if (vm_flags & VM_HUGEPAGE)
mask |= READ_ONCE(huge_anon_orders_madvise);
- if (hugepage_global_always() ||
+ if (hugepage_global_always() || hugepage_global_defer() ||
((vm_flags & VM_HUGEPAGE) && hugepage_global_enabled()))
mask |= READ_ONCE(huge_anon_orders_inherit);
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 3d3ebdc002d5..a5e66a12bae8 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -297,12 +297,15 @@ static ssize_t enabled_show(struct kobject *kobj,
const char *output;
if (test_bit(TRANSPARENT_HUGEPAGE_FLAG, &transparent_hugepage_flags))
- output = "[always] madvise never";
+ output = "[always] madvise defer never";
else if (test_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
&transparent_hugepage_flags))
- output = "always [madvise] never";
+ output = "always [madvise] defer never";
+ else if (test_bit(TRANSPARENT_HUGEPAGE_DEFER_PF_INST_FLAG,
+ &transparent_hugepage_flags))
+ output = "always madvise [defer] never";
else
- output = "always madvise [never]";
+ output = "always madvise defer [never]";
return sysfs_emit(buf, "%s\n", output);
}
@@ -315,13 +318,20 @@ static ssize_t enabled_store(struct kobject *kobj,
if (sysfs_streq(buf, "always")) {
clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG, &transparent_hugepage_flags);
+ clear_bit(TRANSPARENT_HUGEPAGE_DEFER_PF_INST_FLAG, &transparent_hugepage_flags);
set_bit(TRANSPARENT_HUGEPAGE_FLAG, &transparent_hugepage_flags);
+ } else if (sysfs_streq(buf, "defer")) {
+ clear_bit(TRANSPARENT_HUGEPAGE_FLAG, &transparent_hugepage_flags);
+ clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG, &transparent_hugepage_flags);
+ set_bit(TRANSPARENT_HUGEPAGE_DEFER_PF_INST_FLAG, &transparent_hugepage_flags);
} else if (sysfs_streq(buf, "madvise")) {
clear_bit(TRANSPARENT_HUGEPAGE_FLAG, &transparent_hugepage_flags);
+ clear_bit(TRANSPARENT_HUGEPAGE_DEFER_PF_INST_FLAG, &transparent_hugepage_flags);
set_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG, &transparent_hugepage_flags);
} else if (sysfs_streq(buf, "never")) {
clear_bit(TRANSPARENT_HUGEPAGE_FLAG, &transparent_hugepage_flags);
clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG, &transparent_hugepage_flags);
+ clear_bit(TRANSPARENT_HUGEPAGE_DEFER_PF_INST_FLAG, &transparent_hugepage_flags);
} else
ret = -EINVAL;
@@ -943,18 +953,31 @@ static int __init setup_transparent_hugepage(char *str)
&transparent_hugepage_flags);
clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
&transparent_hugepage_flags);
+ clear_bit(TRANSPARENT_HUGEPAGE_DEFER_PF_INST_FLAG,
+ &transparent_hugepage_flags);
ret = 1;
+ } else if (!strcmp(str, "defer")) {
+ clear_bit(TRANSPARENT_HUGEPAGE_FLAG,
+ &transparent_hugepage_flags);
+ clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
+ &transparent_hugepage_flags);
+ set_bit(TRANSPARENT_HUGEPAGE_DEFER_PF_INST_FLAG,
+ &transparent_hugepage_flags);
} else if (!strcmp(str, "madvise")) {
clear_bit(TRANSPARENT_HUGEPAGE_FLAG,
&transparent_hugepage_flags);
+ clear_bit(TRANSPARENT_HUGEPAGE_DEFER_PF_INST_FLAG,
+ &transparent_hugepage_flags);
set_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
- &transparent_hugepage_flags);
+ &transparent_hugepage_flags);
ret = 1;
} else if (!strcmp(str, "never")) {
clear_bit(TRANSPARENT_HUGEPAGE_FLAG,
&transparent_hugepage_flags);
clear_bit(TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG,
&transparent_hugepage_flags);
+ clear_bit(TRANSPARENT_HUGEPAGE_DEFER_PF_INST_FLAG,
+ &transparent_hugepage_flags);
ret = 1;
}
out:
--
2.48.1
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