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 > > Signed-off-by: Vinayak Menon <[email protected]> > --- > 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! > + if (reclaim_state) { > + sc->nr_reclaimed += reclaim_state->reclaimed_slab; > + reclaim_state->reclaimed_slab = 0; > + } > + > if (sc->nr_reclaimed - nr_reclaimed) > reclaimable = true; > > -- > QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a > member of the Code Aurora Forum, hosted by The Linux Foundation > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to [email protected]. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: <a href=mailto:"[email protected]";> [email protected] </a>
