[lvm-devel] stable-2.02 - config: add new setting io_memory_size
David Teigland
teigland at sourceware.org
Mon Mar 4 17:27:22 UTC 2019
Gitweb: https://sourceware.org/git/?p=lvm2.git;a=commitdiff;h=8dbfdb5b737cf916a8b95b8d19eec67a960a6392
Commit: 8dbfdb5b737cf916a8b95b8d19eec67a960a6392
Parent: 675b94a11b6e76b241bf84db2c4e318a9658c394
Author: David Teigland <teigland at redhat.com>
AuthorDate: Fri Mar 1 13:55:59 2019 -0600
Committer: David Teigland <teigland at redhat.com>
CommitterDate: Mon Mar 4 10:31:47 2019 -0600
config: add new setting io_memory_size
which defines the amount of memory that lvm will allocate
for bcache. Increasing this setting is required if it is
smaller than a single copy of VG metadata.
---
lib/commands/toolcontext.c | 2 ++
lib/config/config_settings.h | 8 ++++++++
lib/config/defaults.h | 2 ++
lib/label/label.c | 40 ++++++++++++++++++++--------------------
lib/misc/lvm-globals.c | 10 ++++++++++
lib/misc/lvm-globals.h | 3 +++
6 files changed, 45 insertions(+), 20 deletions(-)
diff --git a/lib/commands/toolcontext.c b/lib/commands/toolcontext.c
index 3289b38..25e8b87 100644
--- a/lib/commands/toolcontext.c
+++ b/lib/commands/toolcontext.c
@@ -685,6 +685,8 @@ static int _process_config(struct cmd_context *cmd)
if (!_init_system_id(cmd))
return_0;
+ init_io_memory_size(find_config_tree_int(cmd, global_io_memory_size_CFG, NULL));
+
return 1;
}
diff --git a/lib/config/config_settings.h b/lib/config/config_settings.h
index 8fe7ec9..75321da 100644
--- a/lib/config/config_settings.h
+++ b/lib/config/config_settings.h
@@ -1129,6 +1129,14 @@ cfg(global_notify_dbus_CFG, "notify_dbus", global_CFG_SECTION, 0, CFG_TYPE_BOOL,
"When enabled, an LVM command that changes PVs, changes VG metadata,\n"
"or changes the activation state of an LV will send a notification.\n")
+cfg(global_io_memory_size_CFG, "io_memory_size", global_CFG_SECTION, CFG_DEFAULT_COMMENTED, CFG_TYPE_INT, DEFAULT_IO_MEMORY_SIZE_KB, vsn(2, 2, 184), NULL, 0, NULL,
+ "The amount of memory in KiB that LVM allocates to perform disk io.\n"
+ "LVM performance may benefit from more io memory when there are many\n"
+ "disks or VG metadata is large. Increasing this size may be necessary\n"
+ "when a single copy of VG metadata is larger than the current setting.\n"
+ "This value should usually not be decreased from the default; setting\n"
+ "it too low can result in lvm failing to read VGs.\n")
+
cfg(activation_udev_sync_CFG, "udev_sync", activation_CFG_SECTION, 0, CFG_TYPE_BOOL, DEFAULT_UDEV_SYNC, vsn(2, 2, 51), NULL, 0, NULL,
"Use udev notifications to synchronize udev and LVM.\n"
"The --nodevsync option overrides this setting.\n"
diff --git a/lib/config/defaults.h b/lib/config/defaults.h
index 7a5d365..3b4438a 100644
--- a/lib/config/defaults.h
+++ b/lib/config/defaults.h
@@ -269,4 +269,6 @@
#define DEFAULT_SCAN_LVS 0
+#define DEFAULT_IO_MEMORY_SIZE_KB 4096
+
#endif /* _LVM_DEFAULTS_H */
diff --git a/lib/label/label.c b/lib/label/label.c
index e01608d..b94fd8d 100644
--- a/lib/label/label.c
+++ b/lib/label/label.c
@@ -772,33 +772,33 @@ out:
}
/*
- * How many blocks to set up in bcache? Is 1024 a good max?
+ * num_devs is the number of devices the caller is going to scan.
+ * When 0 the caller doesn't know, and we use the default cache size.
+ * When non-zero, allocate at least num_devs bcache blocks.
+ * num_devs doesn't really tell us how many bcache blocks we'll use
+ * because it includes lvm devs and non-lvm devs, and each lvm dev
+ * will often use a number of bcache blocks.
*
- * Currently, we tell bcache to set up N blocks where N
- * is the number of devices that are going to be scanned.
- * Reasons why this number may not be be a good choice:
- *
- * - there may be a lot of non-lvm devices, which
- * would make this number larger than necessary
- *
- * - each lvm device may use more than one cache
- * block if the metadata is large enough or it
- * uses more than one metadata area, which
- * would make this number smaller than it
- * should be for the best performance.
- *
- * This is even more tricky to estimate when lvmetad
- * is used, because it's hard to predict how many
- * devs might need to be scanned when using lvmetad.
- * This currently just sets up bcache with MIN blocks.
+ * We don't know ahead of time if we will find some VG metadata
+ * that is larger than the total size of the bcache, which would
+ * prevent us from reading/writing the VG since we do not dynamically
+ * increase the bcache size when we find it's too small. In these
+ * cases the user would need to set io_memory_size to be larger
+ * than the max VG metadata size (lvm does not impose any limit on
+ * the metadata size.)
*/
-#define MIN_BCACHE_BLOCKS 32
+#define MIN_BCACHE_BLOCKS 32 /* 4MB, currently matches DEFAULT_IO_MEMORY_SIZE_KB */
#define MAX_BCACHE_BLOCKS 1024
-static int _setup_bcache(int cache_blocks)
+static int _setup_bcache(int num_devs)
{
struct io_engine *ioe = NULL;
+ int iomem_kb = io_memory_size();
+ int block_size_kb = (BCACHE_BLOCK_SIZE_IN_SECTORS * 512) / 1024;
+ int cache_blocks;
+
+ cache_blocks = iomem_kb / block_size_kb;
if (cache_blocks < MIN_BCACHE_BLOCKS)
cache_blocks = MIN_BCACHE_BLOCKS;
diff --git a/lib/misc/lvm-globals.c b/lib/misc/lvm-globals.c
index 82c5706..3bd5cac 100644
--- a/lib/misc/lvm-globals.c
+++ b/lib/misc/lvm-globals.c
@@ -54,6 +54,7 @@ static char _sysfs_dir_path[PATH_MAX] = "";
static int _dev_disable_after_error_count = DEFAULT_DISABLE_AFTER_ERROR_COUNT;
static uint64_t _pv_min_size = (DEFAULT_PV_MIN_SIZE_KB * 1024L >> SECTOR_SHIFT);
static const char *_unknown_device_name = DEFAULT_UNKNOWN_DEVICE_NAME;
+static int _io_memory_size_kb = DEFAULT_IO_MEMORY_SIZE_KB;
void init_verbose(int level)
{
@@ -387,3 +388,12 @@ void init_unknown_device_name(const char *name)
_unknown_device_name = name;
}
+int io_memory_size(void)
+{
+ return _io_memory_size_kb;
+}
+
+void init_io_memory_size(int val)
+{
+ _io_memory_size_kb = val;
+}
diff --git a/lib/misc/lvm-globals.h b/lib/misc/lvm-globals.h
index f985cfa..3007cc5 100644
--- a/lib/misc/lvm-globals.h
+++ b/lib/misc/lvm-globals.h
@@ -53,6 +53,7 @@ void init_pv_min_size(uint64_t sectors);
void init_activation_checks(int checks);
void init_retry_deactivation(int retry);
void init_unknown_device_name(const char *name);
+void init_io_memory_size(int val);
void set_cmd_name(const char *cmd_name);
const char *get_cmd_name(void);
@@ -86,6 +87,7 @@ uint64_t pv_min_size(void);
int activation_checks(void);
int retry_deactivation(void);
const char *unknown_device_name(void);
+int io_memory_size(void);
#define DMEVENTD_MONITOR_IGNORE -1
int dmeventd_monitor_mode(void);
@@ -93,4 +95,5 @@ int dmeventd_monitor_mode(void);
#define NO_DEV_ERROR_COUNT_LIMIT 0
int dev_disable_after_error_count(void);
+
#endif
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