Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1570459

Re: [PATCH 1/2 v2] mm: vmscan: do not pass reclaimed slab to vmpressure

Show all headers | View raw

On Tue, Jan 31, 2017 at 5:26 AM, Minchan Kim <minchan@kernel.org> wrote:
> On Fri, Jan 27, 2017 at 01:43:36PM +0530, Vinayak Menon wrote:
>> It is noticed that during a global reclaim the memory
>> reclaimed via shrinking the slabs can sometimes result
>> in reclaimed pages being greater than the scanned pages
>> in shrink_node. When this is passed to vmpressure, the
>> unsigned arithmetic results in the pressure value to be
>> huge, thus resulting in a critical event being sent to
>> root cgroup. While this can be fixed by underflow checks
>> in vmpressure, adding reclaimed slab without a corresponding
>> increment of nr_scanned results in incorrect vmpressure
>> reporting. So do not consider reclaimed slab pages in
>> vmpressure calculation.
>
> I belive we could enhance the description better.
>
> problem
>
> VM include nr_reclaimed of slab but not nr_scanned so pressure
> calculation can be underflow.
>
> solution
>
> do not consider reclaimed slab pages for vmpressure
>
> why
>
> Freeing a page by slab shrinking depends on each slab's object
> population so the cost model(i.e., scan:free) is not fair with
> LRU pages. Also, every shrinker doesn't account reclaimed pages.
> Lastly, this regression happens since 6b4f7799c6a5
>
Done. Sending an updated one.

>>
>> Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>
>> ---
>>  mm/vmscan.c | 10 +++++-----
>>  1 file changed, 5 insertions(+), 5 deletions(-)
>>
>> diff --git a/mm/vmscan.c b/mm/vmscan.c
>> index 947ab6f..37c4486 100644
>> --- a/mm/vmscan.c
>> +++ b/mm/vmscan.c
>> @@ -2594,16 +2594,16 @@ static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc)
>>                                   sc->nr_scanned - nr_scanned,
>>                                   node_lru_pages);
>>
>> -             if (reclaim_state) {
>> -                     sc->nr_reclaimed += reclaim_state->reclaimed_slab;
>> -                     reclaim_state->reclaimed_slab = 0;
>> -             }
>> -
>>               /* Record the subtree's reclaim efficiency */
>>               vmpressure(sc->gfp_mask, sc->target_mem_cgroup, true,
>>                          sc->nr_scanned - nr_scanned,
>>                          sc->nr_reclaimed - nr_reclaimed);
>>
>
> Please add comment about "vmpressure excludes reclaimed pages via slab
> because blah blah blah" so upcoming patches doesn't make mistake again.
>
> Thanks!
>
Done. Thanks Minchan.

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

[PATCH 1/2 v2] mm: vmscan: do not pass reclaimed slab to vmpressure Vinayak Menon <vinmenon@codeaurora.org> - 2017-01-27 09:20 +0100
  [PATCH 2/2] mm: vmpressure: fix sending wrong events on underflow Vinayak Menon <vinmenon@codeaurora.org> - 2017-01-27 09:20 +0100
    Re: [PATCH 2/2] mm: vmpressure: fix sending wrong events on underflow Minchan Kim <minchan@kernel.org> - 2017-01-31 01:10 +0100
  Re: [PATCH 1/2 v2] mm: vmscan: do not pass reclaimed slab to  vmpressure Minchan Kim <minchan@kernel.org> - 2017-01-31 01:00 +0100
    Re: [PATCH 1/2 v2] mm: vmscan: do not pass reclaimed slab to vmpressure vinayak menon <vinayakm.list@gmail.com> - 2017-01-31 08:50 +0100
  [PATCH 1/2 v3] mm: vmscan: do not pass reclaimed slab to vmpressure Vinayak Menon <vinmenon@codeaurora.org> - 2017-01-31 10:10 +0100
    Re: [PATCH 1/2 v3] mm: vmscan: do not pass reclaimed slab to  vmpressure Minchan Kim <minchan@kernel.org> - 2017-02-01 07:20 +0100
    Re: [PATCH 1/2 v3] mm: vmscan: do not pass reclaimed slab to  vmpressure Michal Hocko <mhocko@kernel.org> - 2017-02-02 11:50 +0100
      Re: [PATCH 1/2 v3] mm: vmscan: do not pass reclaimed slab to  vmpressure Michal Hocko <mhocko@kernel.org> - 2017-02-02 11:50 +0100
        Re: [PATCH 1/2 v3] mm: vmscan: do not pass reclaimed slab to vmpressure vinayak menon <vinayakm.list@gmail.com> - 2017-02-02 12:30 +0100
          Re: [PATCH 1/2 v3] mm: vmscan: do not pass reclaimed slab to  vmpressure Michal Hocko <mhocko@kernel.org> - 2017-02-02 13:00 +0100
            Re: [PATCH 1/2 v3] mm: vmscan: do not pass reclaimed slab to vmpressure vinayak menon <vinayakm.list@gmail.com> - 2017-02-02 16:40 +0100
              Re: [PATCH 1/2 v3] mm: vmscan: do not pass reclaimed slab to  vmpressure Michal Hocko <mhocko@kernel.org> - 2017-02-02 17:10 +0100
                Re: [PATCH 1/2 v3] mm: vmscan: do not pass reclaimed slab to vmpressure vinayak menon <vinayakm.list@gmail.com> - 2017-02-03 06:30 +0100
                Re: [PATCH 1/2 v3] mm: vmscan: do not pass reclaimed slab to  vmpressure Michal Hocko <mhocko@kernel.org> - 2017-02-03 16:10 +0100
                Re: [PATCH 1/2 v3] mm: vmscan: do not pass reclaimed slab to vmpressure vinayak menon <vinayakm.list@gmail.com> - 2017-02-06 12:40 +0100
      Re: [PATCH 1/2 v3] mm: vmscan: do not pass reclaimed slab to vmpressure vinayak menon <vinayakm.list@gmail.com> - 2017-02-02 12:30 +0100
      Re: [PATCH 1/2 v3] mm: vmscan: do not pass reclaimed slab to  vmpressure Minchan Kim <minchan@kernel.org> - 2017-02-03 07:20 +0100

csiph-web