Blame SOURCES/0049-Ticket-49267-autosize-split-of-0-results-in-dbcache-.patch

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From e52c519a8553dd8abee5740714054ebbdd59e51a Mon Sep 17 00:00:00 2001
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From: William Brown <firstyear@redhat.com>
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Date: Tue, 23 May 2017 11:03:24 +1000
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Subject: [PATCH] Ticket 49267 - autosize split of 0 results in dbcache of 0
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Bug Description:  autosize split of 0 results in a dbcache of 0. This was
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due to a missing bounds check on the value for 0. In theory this could
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still be problematic if the value was say 1% ... But hopefully we don't
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see that :)
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Fix Description:  Add the bounds check.
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https://pagure.io/389-ds-base/issue/49267
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Author: wibrown
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Review by: mreynolds (Thanks!)
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(cherry picked from commit 22d4865ea20acb6e6c11aed10d09241b09bb711c)
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---
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 ldap/servers/slapd/back-ldbm/start.c | 14 +++++++++++++-
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 1 file changed, 13 insertions(+), 1 deletion(-)
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diff --git a/ldap/servers/slapd/back-ldbm/start.c b/ldap/servers/slapd/back-ldbm/start.c
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index a207bd8..1834a19 100644
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--- a/ldap/servers/slapd/back-ldbm/start.c
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+++ b/ldap/servers/slapd/back-ldbm/start.c
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@@ -101,7 +101,11 @@ ldbm_back_start_autotune(struct ldbminfo *li) {
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     /* This doesn't control the availability of the feature, so we can take the
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      * default from ldbm_config.c
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      */
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-    autosize_db_percentage_split = li->li_cache_autosize_split;
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+    if (li->li_cache_autosize_split == 0) {
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+        autosize_db_percentage_split = 40;
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+    } else {
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+        autosize_db_percentage_split = li->li_cache_autosize_split;
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+    }
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     /* Check the values are sane. */
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@@ -131,10 +135,18 @@ ldbm_back_start_autotune(struct ldbminfo *li) {
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     db_size = (autosize_db_percentage_split * zone_size) / 100;
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     /* Cap the DB size at 512MB, as this doesn't help perf much more (lkrispen's advice) */
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+    /* NOTE: Do we need a minimum DB size? */
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     if (db_size > (512 * MEGABYTE)) {
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         db_size = (512 * MEGABYTE);
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     }
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+    /* NOTE: Because of how we workout entry_size, even if
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+     * have autosize split to say ... 90% for dbcache, because
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+     * we cap db_size, we use zone_size - db_size, meaning that entry
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+     * cache still gets the remaining memory *even* though we didn't use it all.
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+     * If we didn't do this, entry_cache would only get 10% of of the avail, even
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+     * if db_size was caped at say 5% down from 90.
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+     */
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     if (backend_count > 0 ) {
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         /* Number of entry cache pages per backend. */
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         entry_size = (zone_size - db_size) / backend_count;
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-- 
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2.9.4
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