On Wed 22-02-17 15:16:57, Johannes Weiner wrote:
[...]
> And a follow-up: once it gives up, when should kswapd return to work?
> We used to reset NR_PAGES_SCANNED whenever a page gets freed. But
> that's a branch in a common allocator path, just to recover kswapd - a
> latency tool, not a necessity for functional correctness - from a
> situation that's exceedingly pretty rare. How about we leave it
> disabled until a direct reclaimer manages to free something?
Hmm, I guess we also want to reset the counter after OOM invocation
which might free a lot of memory and we do not want to wait for the
direct reclaim to resurrect the kswapd. Something like the following on
top of yours
---
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index ddf27c435225..6be11c18551f 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3446,7 +3446,8 @@ __alloc_pages_direct_reclaim(gfp_t gfp_mask, unsigned int order,
return page;
}
-static void wake_all_kswapds(unsigned int order, const struct alloc_context *ac)
+static void wake_all_kswapds(unsigned int order, const struct alloc_context *ac,
+ bool force)
{
struct zoneref *z;
struct zone *zone;
@@ -3454,8 +3455,11 @@ static void wake_all_kswapds(unsigned int order, const struct alloc_context *ac)
for_each_zone_zonelist_nodemask(zone, z, ac->zonelist,
ac->high_zoneidx, ac->nodemask) {
- if (last_pgdat != zone->zone_pgdat)
+ if (last_pgdat != zone->zone_pgdat) {
+ if (force)
+ zone->zone_pgdat->kswapd_failed_runs = 0;
wakeup_kswapd(zone, order, ac->high_zoneidx);
+ }
last_pgdat = zone->zone_pgdat;
}
}
@@ -3640,6 +3644,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
unsigned long alloc_start = jiffies;
unsigned int stall_timeout = 10 * HZ;
unsigned int cpuset_mems_cookie;
+ bool kick_kswapd = false;
/*
* In the slowpath, we sanity check order to avoid ever trying to
@@ -3685,7 +3690,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
goto nopage;
if (gfp_mask & __GFP_KSWAPD_RECLAIM)
- wake_all_kswapds(order, ac);
+ wake_all_kswapds(order, ac, false);
/*
* The adjusted alloc_flags might result in immediate success, so try
@@ -3738,7 +3743,8 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
retry:
/* Ensure kswapd doesn't accidentally go to sleep as long as we loop */
if (gfp_mask & __GFP_KSWAPD_RECLAIM)
- wake_all_kswapds(order, ac);
+ wake_all_kswapds(order, ac, kick_kswapd);
+ kick_kswapd = false;
if (gfp_pfmemalloc_allowed(gfp_mask))
alloc_flags = ALLOC_NO_WATERMARKS;
@@ -3833,6 +3839,7 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
/* Retry as long as the OOM killer is making progress */
if (did_some_progress) {
no_progress_loops = 0;
+ kick_kswapd = true;
goto retry;
}
--
Michal Hocko
SUSE Labs
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