[tor-commits] [tor/maint-0.4.0] OOM-purge the DNS cache one part at a time

[teor at torproject.org]

commit 37aae23945c45c459091b38699130a14466d33ef
Author: Nick Mathewson <nickm at torproject.org>
Date:   Fri May 17 10:03:41 2019 -0400

    OOM-purge the DNS cache one part at a time
    
    Previously we purged it in 1-hour increments -- but one-hour is the
    maximum TTL for the cache!  Now we do it in 25%-TTL increments.
    
    Fixes bug 29617; bugfix on 0.3.5.1-alpha.
---
 changes/ticket29617     | 4 ++++
 src/feature/relay/dns.c | 3 ++-
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/changes/ticket29617 b/changes/ticket29617
new file mode 100644
index 000000000..4d50ea962
--- /dev/null
+++ b/changes/ticket29617
@@ -0,0 +1,4 @@
+  o Minor bugfixes (out-of-memory handler):
+    - When purging the DNS cache because of an out-of-memory condition,
+      try purging just the older entries at first.  Previously, we would
+      purge the whole thing. Fixes bug 29617; bugfix on 0.3.5.1-alpha.
diff --git a/src/feature/relay/dns.c b/src/feature/relay/dns.c
index d3660c47e..cc9f4cf49 100644
--- a/src/feature/relay/dns.c
+++ b/src/feature/relay/dns.c
@@ -2130,7 +2130,8 @@ dns_cache_handle_oom(time_t now, size_t min_remove_bytes)
     current_size -= bytes_removed;
     total_bytes_removed += bytes_removed;
 
-    time_inc += 3600; /* Increase time_inc by 1 hour. */
+    /* Increase time_inc by a reasonable fraction. */
+    time_inc += (MAX_DNS_TTL_AT_EXIT / 4);
   } while (total_bytes_removed < min_remove_bytes);
 
   return total_bytes_removed;