Re: [v3 1/2] mm: khugepaged: recalculate min_free_kbytes after memory hotplug as expected by khugepaged

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Can this patch be included?  As Kirill is ok with patch now.

Thanks,
Vijay

On 9/16/2020 6:21 PM, Vijay Balakrishna wrote:
When memory is hotplug added or removed the min_free_kbytes must 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@xxxxxxxxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Reviewed-by: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
---
  include/linux/khugepaged.h |  5 +++++
  mm/khugepaged.c            | 13 +++++++++++--
  mm/memory_hotplug.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/memory_hotplug.c b/mm/memory_hotplug.c
index e9d5ab5d3ca0..3e19272c1fad 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -36,6 +36,7 @@
  #include <linux/memblock.h>
  #include <linux/compaction.h>
  #include <linux/rmap.h>
+#include <linux/khugepaged.h>
#include <asm/tlbflush.h> @@ -857,6 +858,7 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages,
  	zone_pcp_update(zone);
init_per_zone_wmark_min();
+	khugepaged_min_free_kbytes_update();
kswapd_run(nid);
  	kcompactd_run(nid);
@@ -1600,6 +1602,7 @@ static int __ref __offline_pages(unsigned long start_pfn,
  	pgdat_resize_unlock(zone->zone_pgdat, &flags);
init_per_zone_wmark_min();
+	khugepaged_min_free_kbytes_update();
if (!populated_zone(zone)) {
  		zone_pcp_reset(zone);





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