On Wed, Mar 09, 2016 at 11:55:43PM +0200, Ebru Akagunduz wrote:
> Currently khugepaged makes swapin readahead to improve
> THP collapse rate. This patch checks vm statistics
> to avoid workload of swapin, if unnecessary. So that
> when system under pressure, khugepaged won't consume
> resources to swapin.
>
> The patch was tested with a test program that allocates
> 800MB of memory, writes to it, and then sleeps. The system
> was forced to swap out all. Afterwards, the test program
> touches the area by writing, it skips a page in each
> 20 pages of the area. When waiting to swapin readahead
> left part of the test, the memory forced to be busy
> doing page reclaim. There was enough free memory during
> test, khugepaged did not swapin readahead due to business.
>
> Test results:
>
> After swapped out
> -------------------------------------------------------------------
> | Anonymous | AnonHugePages | Swap | Fraction |
> -------------------------------------------------------------------
> With patch | 450964 kB | 450560 kB | 349036 kB | %99 |
> -------------------------------------------------------------------
> Without patch | 351308 kB | 350208 kB | 448692 kB | %99 |
> -------------------------------------------------------------------
>
> After swapped in (waiting 10 minutes)
> -------------------------------------------------------------------
> | Anonymous | AnonHugePages | Swap | Fraction |
> -------------------------------------------------------------------
> With patch | 637932 kB | 559104 kB | 162068 kB | %69 |
> -------------------------------------------------------------------
> Without patch | 586816 kB | 464896 kB | 213184 kB | %79 |
> -------------------------------------------------------------------
>
> Signed-off-by: Ebru Akagunduz <ebru.akagunduz@xxxxxxxxx>
> ---
> mm/huge_memory.c | 15 ++++++++++++++-
> 1 file changed, 14 insertions(+), 1 deletion(-)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 7f75292..109a2af 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -102,6 +102,7 @@ static DECLARE_WAIT_QUEUE_HEAD(khugepaged_wait);
> */
> static unsigned int khugepaged_max_ptes_none __read_mostly;
> static unsigned int khugepaged_max_ptes_swap __read_mostly;
> +static unsigned long int allocstall = 0;
>
> static int khugepaged(void *none);
> static int khugepaged_slab_init(void);
> @@ -2411,6 +2412,7 @@ static void collapse_huge_page(struct mm_struct *mm,
> struct mem_cgroup *memcg;
> unsigned long mmun_start; /* For mmu_notifiers */
> unsigned long mmun_end; /* For mmu_notifiers */
> + unsigned long events[NR_VM_EVENT_ITEMS], swap = 0;
collapse_huge_page() is nested under collapse_huge_page(), so you
effectively allocate 2 * NR_VM_EVENT_ITEMS * sizeof(long) on stack.
That's a lot for stack. And it's only get total value of ALLOCSTALL event.
Should we instead introduce a helper to sum values of a particular event
over all cpu? I'm surprised that we don't have any yet.
Something like this (totally untested):
unsigned long sum_vm_event(enum vm_event_item item)
{
int cpu;
unsigned long ret = 0;
get_online_cpus();
for_each_online_cpu(cpu)
ret += per_cpu(vm_event_states, cpu).event[item];
put_online_cpus();
return ret;
}
--
Kirill A. Shutemov
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