Messages in this thread | | | Subject | Re: [v2 2/2] mm: khugepaged: avoid overriding min_free_kbytes set by user | From | Vijay Balakrishna <> | Date | Wed, 16 Sep 2020 12:18:12 -0700 |
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On 9/16/2020 12:59 AM, Michal Hocko wrote: > On Tue 15-09-20 14:10:58, Vijay Balakrishna 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. Also modifying "recommended_min" variable >> type to "int" from "unsigned long" to avoid undesired result noticed >> during testing. It is due to comparing "unsigned long" with "int" type. >> >> Signed-off-by: Vijay Balakrishna <vijayb@linux.microsoft.com> >> Cc: stable@vger.kernel.org >> Reviewed-by: Pavel Tatashin <pasha.tatashin@soleen.com> >> --- >> 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; >> >> 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); > > nr_free_buffer_pages can oveflow in int on very large machines.
Good point. I will address it.
> >> recommended_min <<= (PAGE_SHIFT-10); >> >> - if (recommended_min > min_free_kbytes) { >> + if (recommended_min > user_min_free_kbytes) { > > This can decrease the size theoretically. Because user_min_free_kbytes > is -1 by default and recommended_min might be <= min_free_kbytes. > > You need to check both. Also can we make user_min_free_kbytes 0 by > default? From a quick look, nobody should really care.
Let me rework.
Thanks, Vijay
> >> if (user_min_free_kbytes >= 0) >> - pr_info("raising min_free_kbytes from %d to %lu to help transparent hugepage allocations\n", >> + pr_info("raising min_free_kbytes from %d to %d to help transparent hugepage allocations\n", >> min_free_kbytes, recommended_min); >> >> min_free_kbytes = recommended_min; >> -- >> 2.28.0 >> >
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