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From de72fa6b0582b95216215cc1400412fe91bc8ba3 Mon Sep 17 00:00:00 2001
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From: =?UTF-8?q?Zbigniew=20J=C4=99drzejewski-Szmek?= <zbyszek@in.waw.pl>
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Date: Tue, 22 Jan 2019 16:12:52 +0100
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Subject: [PATCH] journal: limit the number of entries in the cache based on
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available memory
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This is far from perfect, but should give mostly reasonable values. My
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assumption is that if somebody has a few hundred MB of memory, they are
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unlikely to have thousands of processes logging. A hundred would already be a
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lot. So let's scale the cache size propritionally to the total memory size,
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with clamping on both ends.
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The formula gives 64 cache entries for each GB of RAM.
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(cherry-picked from commit b12a480829c5ca8f4d4fa9cde8716b5f2f12a3ad)
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Related: #1664976
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---
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src/journal/journald-context.c | 35 ++++++++++++++++++++++++++++++++--
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1 file changed, 33 insertions(+), 2 deletions(-)
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diff --git a/src/journal/journald-context.c b/src/journal/journald-context.c
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index ce07de1bfb..0f0dc1de4d 100644
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--- a/src/journal/journald-context.c
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+++ b/src/journal/journald-context.c
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@@ -14,6 +14,7 @@
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#include "journal-util.h"
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#include "journald-context.h"
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#include "process-util.h"
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+#include "procfs-util.h"
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#include "string-util.h"
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#include "syslog-util.h"
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#include "unaligned.h"
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@@ -58,7 +59,37 @@
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/* Keep at most 16K entries in the cache. (Note though that this limit may be violated if enough streams pin entries in
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* the cache, in which case we *do* permit this limit to be breached. That's safe however, as the number of stream
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* clients itself is limited.) */
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-#define CACHE_MAX (16*1024)
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+#define CACHE_MAX_FALLBACK 128U
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+#define CACHE_MAX_MAX (16*1024U)
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+#define CACHE_MAX_MIN 64U
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+
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+static size_t cache_max(void) {
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+ static size_t cached = -1;
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+
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+ if (cached == (size_t) -1) {
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+ uint64_t mem_total;
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+ int r;
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+
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+ r = procfs_memory_get(&mem_total, NULL);
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+ if (r < 0) {
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+ log_warning_errno(r, "Cannot query /proc/meminfo for MemTotal: %m");
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+ cached = CACHE_MAX_FALLBACK;
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+ } else {
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+ /* Cache entries are usually a few kB, but the process cmdline is controlled by the
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+ * user and can be up to _SC_ARG_MAX, usually 2MB. Let's say that approximately up to
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+ * 1/8th of memory may be used by the cache.
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+ *
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+ * In the common case, this formula gives 64 cache entries for each GB of RAM.
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+ */
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+ long l = sysconf(_SC_ARG_MAX);
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+ assert(l > 0);
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+
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+ cached = CLAMP(mem_total / 8 / (uint64_t) l, CACHE_MAX_MIN, CACHE_MAX_MAX);
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+ }
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+ }
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+
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+ return cached;
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+}
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static int client_context_compare(const void *a, const void *b) {
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const ClientContext *x = a, *y = b;
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@@ -587,7 +618,7 @@ static int client_context_get_internal(
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return 0;
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}
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- client_context_try_shrink_to(s, CACHE_MAX-1);
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+ client_context_try_shrink_to(s, cache_max()-1);
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r = client_context_new(s, pid, &c);
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if (r < 0)
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