On Tue 28-02-17 16:40:07, Johannes Weiner wrote: > The backoff mechanism is not needed. If we have MAX_RECLAIM_RETRIES > loops without progress, we'll OOM anyway; backing off might cut one or > two iterations off that in the rare OOM case. If we have intermittent > success reclaiming a few pages, the backoff function gets reset also, > and so is of little help in these scenarios. Yes, as already mentioned elsewhere the original intention was to a more graceful oom convergence when we are trashing over last few reclaimable pages but as the code evolved the result is not all that great. > We might want a backoff function for when there IS progress, but not > enough to be satisfactory. But this isn't that. Remove it. Completely agreed. > Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx> Acked-by: Michal Hocko <mhocko@xxxxxxxx> > --- > mm/page_alloc.c | 15 ++++++--------- > 1 file changed, 6 insertions(+), 9 deletions(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 9ac639864bed..223644afed28 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -3511,11 +3511,10 @@ bool gfp_pfmemalloc_allowed(gfp_t gfp_mask) > /* > * Checks whether it makes sense to retry the reclaim to make a forward progress > * for the given allocation request. > - * The reclaim feedback represented by did_some_progress (any progress during > - * the last reclaim round) and no_progress_loops (number of reclaim rounds without > - * any progress in a row) is considered as well as the reclaimable pages on the > - * applicable zone list (with a backoff mechanism which is a function of > - * no_progress_loops). > + * > + * We give up when we either have tried MAX_RECLAIM_RETRIES in a row > + * without success, or when we couldn't even meet the watermark if we > + * reclaimed all remaining pages on the LRU lists. > * > * Returns true if a retry is viable or false to enter the oom path. > */ > @@ -3560,13 +3559,11 @@ should_reclaim_retry(gfp_t gfp_mask, unsigned order, > bool wmark; > > available = reclaimable = zone_reclaimable_pages(zone); > - available -= DIV_ROUND_UP((*no_progress_loops) * available, > - MAX_RECLAIM_RETRIES); > available += zone_page_state_snapshot(zone, NR_FREE_PAGES); > > /* > - * Would the allocation succeed if we reclaimed the whole > - * available? > + * Would the allocation succeed if we reclaimed all > + * reclaimable pages? > */ > wmark = __zone_watermark_ok(zone, order, min_wmark, > ac_classzone_idx(ac), alloc_flags, available); > -- > 2.11.1 -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
