Before 0e093d99763e (writeback: do not sleep on the congestion queue if
there are no congested BDIs or if significant congestion is not being
encountered in the current zone), preferred_zone was only used for
statistics and to determine the zoneidx from which to allocate from given
the type requested.
wait_iff_congested(), though, uses preferred_zone to determine if the
congestion wait should be deferred because its dirty pages are backed by
a congested bdi. This incorrectly defers the timeout and busy loops in
the page allocator with various cond_resched() calls if preferred_zone is
not allowed in the current context, usually consuming 100% of a cpu.
This patch resets preferred_zone to an allowed zone in the slowpath if
the allocation context is constrained by current's cpuset. It also
ensures preferred_zone is from the set of allowed nodes when called from
within direct reclaim; allocations are always constrainted by cpusets
since the context is always blockable.
Both of these uses of cpuset_current_mems_allowed are protected by
get_mems_allowed().
---
mm/page_alloc.c | 12 ++++++++++++
mm/vmscan.c | 3 ++-
2 files changed, 14 insertions(+), 1 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2034,6 +2034,18 @@ restart:
*/
alloc_flags = gfp_to_alloc_flags(gfp_mask);
+ /*
+ * If preferred_zone cannot be allocated from in this context, find the
+ * first allowable zone instead.
+ */
+ if ((alloc_flags & ALLOC_CPUSET) &&
+ !cpuset_zone_allowed_softwall(preferred_zone, gfp_mask)) {
+ first_zones_zonelist(zonelist, high_zoneidx,
+ &cpuset_current_mems_allowed, &preferred_zone);
+ if (unlikely(!preferred_zone))
+ goto nopage;
+ }
+
/* This is the last chance, in general, before the goto nopage. */
page = get_page_from_freelist(gfp_mask, nodemask, order, zonelist,
high_zoneidx, alloc_flags & ~ALLOC_NO_WATERMARKS,
diff --git a/mm/vmscan.c b/mm/vmscan.c
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2084,7 +2084,8 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
struct zone *preferred_zone;
first_zones_zonelist(zonelist, gfp_zone(sc->gfp_mask),
- NULL, &preferred_zone);
+ &cpuset_current_mems_allowed,
+ &preferred_zone);
wait_iff_congested(preferred_zone, BLK_RW_ASYNC, HZ/10);
}
}
--
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