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SubjectRe: [v4] mm: khugepaged: recalculate min_free_kbytes after memory hotplug as expected by khugepaged
On Mon 28-09-20 17:07:27, Vijay Balakrishna wrote:
> When memory is hotplug added or removed the min_free_kbytes must be

s@must@should@

> 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>
> ---
> 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

--
Michal Hocko
SUSE Labs

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