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Subject[v5] mm: khugepaged: recalculate min_free_kbytes after memory hotplug as expected by khugepaged
Date
When memory is hotplug added or removed the min_free_kbytes should be
recalculated based on what is expected by khugepaged. Currently
after hotplug, min_free_kbytes will be set to a lower default and higher
default set when THP enabled is lost. This change restores min_free_kbytes
as expected for THP consumers.

Fixes: f000565adb77 ("thp: set recommended min free kbytes")

Signed-off-by: Vijay Balakrishna <vijayb@linux.microsoft.com>
Cc: stable@vger.kernel.org
Reviewed-by: Pavel Tatashin <pasha.tatashin@soleen.com>
Acked-by: Michal Hocko <mhocko@suse.com>
---
v4 -> v5
- changelog: must -> should [Michal Hocko]

v3 -> v4
- made changes to move khugepaged_min_free_kbytes_update into
init_per_zone_wmark_min and rested changes
[suggestion from Michal Hocko]

[v2 1/2]
- removed symptoms references from changelog

[v2 2/2]
- addressed following issues Michal Hocko raised:
. nr_free_buffer_pages can oveflow in int on very large machines
. min_free_kbytes can decrease the size theoretically

v1 -> v2
--------
- addressed issue Kirill A. Shutemov raised:
. changes would override min_free_kbytes set by user

include/linux/khugepaged.h | 5 +++++
mm/khugepaged.c | 13 +++++++++++--
mm/page_alloc.c | 3 +++
3 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/include/linux/khugepaged.h b/include/linux/khugepaged.h
index bc45ea1efbf7..c941b7377321 100644
--- a/include/linux/khugepaged.h
+++ b/include/linux/khugepaged.h
@@ -15,6 +15,7 @@ extern int __khugepaged_enter(struct mm_struct *mm);
extern void __khugepaged_exit(struct mm_struct *mm);
extern int khugepaged_enter_vma_merge(struct vm_area_struct *vma,
unsigned long vm_flags);
+extern void khugepaged_min_free_kbytes_update(void);
#ifdef CONFIG_SHMEM
extern void collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr);
#else
@@ -85,6 +86,10 @@ static inline void collapse_pte_mapped_thp(struct mm_struct *mm,
unsigned long addr)
{
}
+
+static inline void khugepaged_min_free_kbytes_update(void)
+{
+}
#endif /* CONFIG_TRANSPARENT_HUGEPAGE */

#endif /* _LINUX_KHUGEPAGED_H */
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index cfa0dba5fd3b..4f7107476a6f 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -56,6 +56,9 @@ enum scan_result {
#define CREATE_TRACE_POINTS
#include <trace/events/huge_memory.h>

+static struct task_struct *khugepaged_thread __read_mostly;
+static DEFINE_MUTEX(khugepaged_mutex);
+
/* default scan 8*512 pte (or vmas) every 30 second */
static unsigned int khugepaged_pages_to_scan __read_mostly;
static unsigned int khugepaged_pages_collapsed;
@@ -2292,8 +2295,6 @@ static void set_recommended_min_free_kbytes(void)

int start_stop_khugepaged(void)
{
- static struct task_struct *khugepaged_thread __read_mostly;
- static DEFINE_MUTEX(khugepaged_mutex);
int err = 0;

mutex_lock(&khugepaged_mutex);
@@ -2320,3 +2321,11 @@ int start_stop_khugepaged(void)
mutex_unlock(&khugepaged_mutex);
return err;
}
+
+void khugepaged_min_free_kbytes_update(void)
+{
+ mutex_lock(&khugepaged_mutex);
+ if (khugepaged_enabled() && khugepaged_thread)
+ set_recommended_min_free_kbytes();
+ mutex_unlock(&khugepaged_mutex);
+}
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index fab5e97dc9ca..ac25d3526fa5 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -69,6 +69,7 @@
#include <linux/nmi.h>
#include <linux/psi.h>
#include <linux/padata.h>
+#include <linux/khugepaged.h>

#include <asm/sections.h>
#include <asm/tlbflush.h>
@@ -7891,6 +7892,8 @@ int __meminit init_per_zone_wmark_min(void)
setup_min_slab_ratio();
#endif

+ khugepaged_min_free_kbytes_update();
+
return 0;
}
postcore_initcall(init_per_zone_wmark_min)
--
2.28.0
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