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.
We might want a backoff function for when there IS progress, but not
enough to be satisfactory. But this isn't that. Remove it.
Signed-off-by: Johannes Weiner <[email protected]>
---
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
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 <[email protected]>
Acked-by: Michal Hocko <[email protected]>
> ---
> 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
On March 01, 2017 5:40 AM 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.
>
> We might want a backoff function for when there IS progress, but not
> enough to be satisfactory. But this isn't that. Remove it.
>
> Signed-off-by: Johannes Weiner <[email protected]>
> ---
Acked-by: Hillf Danton <[email protected]>