From: Vijay Balakrishna vijayb@linux.microsoft.com Subject: mm: khugepaged: recalculate min_free_kbytes after memory hotplug as expected by khugepaged

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.

[vijayb@linux.microsoft.com: v5] Link: https://lkml.kernel.org/r/1601398153-5517-1-git-send-email-vijayb@linux.micr... Link: https://lkml.kernel.org/r/1600305709-2319-2-git-send-email-vijayb@linux.micr... Link: https://lkml.kernel.org/r/1600204258-13683-1-git-send-email-vijayb@linux.mic... Fixes: f000565adb77 ("thp: set recommended min free kbytes") Signed-off-by: Vijay Balakrishna vijayb@linux.microsoft.com Reviewed-by: Pavel Tatashin pasha.tatashin@soleen.com Acked-by: Michal Hocko mhocko@suse.com Cc: Allen Pais apais@microsoft.com Cc: Andrea Arcangeli aarcange@redhat.com Cc: "Kirill A. Shutemov" kirill.shutemov@linux.intel.com Cc: Oleg Nesterov oleg@redhat.com Cc: Song Liu songliubraving@fb.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

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

--- a/include/linux/khugepaged.h~mm-khugepaged-recalculate-min_free_kbytes-after-memory-hotplug-as-expected-by-khugepaged +++ a/include/linux/khugepaged.h @@ -15,6 +15,7 @@ extern int __khugepaged_enter(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_t unsigned long addr) { } + +static inline void khugepaged_min_free_kbytes_update(void) +{ +} #endif /* CONFIG_TRANSPARENT_HUGEPAGE */

#endif /* _LINUX_KHUGEPAGED_H */ --- a/mm/khugepaged.c~mm-khugepaged-recalculate-min_free_kbytes-after-memory-hotplug-as-expected-by-khugepaged +++ a/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; @@ -2304,8 +2307,6 @@ static void set_recommended_min_free_kby

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); @@ -2332,3 +2333,11 @@ fail: 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); +} --- a/mm/page_alloc.c~mm-khugepaged-recalculate-min_free_kbytes-after-memory-hotplug-as-expected-by-khugepaged +++ a/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> @@ -7904,6 +7905,8 @@ int __meminit init_per_zone_wmark_min(vo setup_min_slab_ratio(); #endif

+ khugepaged_min_free_kbytes_update(); + return 0; } postcore_initcall(init_per_zone_wmark_min) _