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SubjectRe: [v1] mm: khugepaged: avoid overriding min_free_kbytes set by user
On Tue, Sep 15, 2020 at 12:55 AM Vijay Balakrishna
<vijayb@linux.microsoft.com> wrote:
>
> set_recommended_min_free_kbytes need to honor min_free_kbytes set by the
> user. Post start-of-day THP enable or memory hotplug operations can
> lose user specified min_free_kbytes, in particular when it is higher than
> calculated recommended value.
>
> Signed-off-by: Vijay Balakrishna <vijayb@linux.microsoft.com>
> Cc: stable@vger.kernel.org
> ---
> mm/khugepaged.c | 8 ++++----
> 1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 4f7107476a6f..b4b753ba411a 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -2253,7 +2253,7 @@ static void set_recommended_min_free_kbytes(void)
> {
> struct zone *zone;
> int nr_zones = 0;
> - unsigned long recommended_min;
> + int recommended_min;

Hi Vijay,

Please explain in log the type change. user_min_free_kbytes is of
"int" type and is initialized to -1, so comparing to unsigned leads to
undesired effect.


>
> for_each_populated_zone(zone) {
> /*
> @@ -2280,12 +2280,12 @@ static void set_recommended_min_free_kbytes(void)
>
> /* don't ever allow to reserve more than 5% of the lowmem */
> recommended_min = min(recommended_min,
> - (unsigned long) nr_free_buffer_pages() / 20);
> + (int) nr_free_buffer_pages() / 20);
> recommended_min <<= (PAGE_SHIFT-10);
>
> - if (recommended_min > min_free_kbytes) {
> + if (recommended_min > user_min_free_kbytes) {

Took me a while to understand, but this change is correct. It is the
same logic that is done in init_per_zone_wmark_min().

Please join the two patches you have in one patch series.
Reviewed-by: Pavel Tatashin <pasha.tatashin@soleen.com>

Thank you,
Pasha

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