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<b><a class="bz_bug_link
bz_status_NEW "
title="NEW - [i855GM, 3.18] X getting stuck in congestion_wait for shrinker"
href="https://bugs.freedesktop.org/show_bug.cgi?id=88026#c2">Comment # 2</a>
on <a class="bz_bug_link
bz_status_NEW "
title="NEW - [i855GM, 3.18] X getting stuck in congestion_wait for shrinker"
href="https://bugs.freedesktop.org/show_bug.cgi?id=88026">bug 88026</a>
from <span class="vcard"><a class="email" href="mailto:chris@chris-wilson.co.uk" title="Chris Wilson <chris@chris-wilson.co.uk>"> <span class="fn">Chris Wilson</span></a>
</span></b>
<pre>Fwiw:
shrink_inactive_list():
/*
* If kswapd scans pages marked marked for immediate
* reclaim and under writeback (nr_immediate), it implies
* that pages are cycling through the LRU faster than
* they are written so also forcibly stall.
*/
if (nr_immediate && current_may_throttle())
congestion_wait(BLK_RW_ASYNC, HZ/10);
nr_immediate is set in shrink_page_list():
if (PageWriteback(page)) {
if (current_is_kswapd() &&
PageReclaim(page) &&
test_bit(ZONE_WRITEBACK, &zone->flags)) {
nr_immediate++;
goto keep_locked;
}
}
which is obviously not true for Xorg.
There is one other call to congestion_wait() at the start of
shrink_inactive_list() (might be worth using gdb to confirm which callsite is
the blocker):
while (unlikely(too_many_isolated(zone, file, sc)))
congestion_wait(BLK_RW_ASYNC, HZ/10);
too_many_isolated() is basically NR_ISOLATED_ANON > NR_INACTIVE_ANON and if
there is actually no backingdev activity then congestion_wait() will not make
any forward progress and it will just loop.
Maybe (though it seems to contradict the intentions of all the comments):
diff --git a/mm/vmscan.c b/mm/vmscan.c
index bd9a72bc4a1b..79a4e9379381 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1488,11 +1488,14 @@ shrink_inactive_list(unsigned long nr_to_scan, struct
lruvec *lruvec,
struct zone_reclaim_stat *reclaim_stat = &lruvec->reclaim_stat;
while (unlikely(too_many_isolated(zone, file, sc))) {
- congestion_wait(BLK_RW_ASYNC, HZ/10);
+ long rem = congestion_wait(BLK_RW_ASYNC, HZ/10);
/* We are about to die and free our memory. Return now. */
if (fatal_signal_pending(current))
return SWAP_CLUSTER_MAX;
+
+ if (rem == 0)
+ break;
}
lru_add_drain();</pre>
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