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backup: trim heap after finishing

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Reported in the community forum [0]. By default, there can be large
amounts of memory left assigned to the QEMU process after backup.
Likely because of fragmentation, it's necessary to explicitly call
malloc_trim() to tell glibc that it shouldn't keep all that memory
resident for the process.

QEMU itself already does a malloc_trim() in the RCU thread, but that
code path might not be reached (or not for a long time) under usual
operation. The value of 4 MiB for the argument was also copied from
there.

Example with the following configuration:
> agent: 1
> boot: order=scsi0
> cores: 4
> cpu: x86-64-v2-AES
> ide2: none,media=cdrom
> memory: 1024
> name: backup-mem
> net0: virtio=DA:58:18:26:59:9F,bridge=vmbr0,firewall=1
> numa: 0
> ostype: l26
> scsi0: rbd:base-107-disk-0/vm-106-disk-1,size=4302M
> scsihw: virtio-scsi-pci
> smbios1: uuid=b2d4511e-8d01-44f1-afd6-9581b30c24a6
> sockets: 2
> startup: order=2
> virtio0: lvmthin:vm-106-disk-1,iothread=1,size=1G
> virtio1: lvmthin:vm-106-disk-2,iothread=1,size=1G
> virtio2: lvmthin:vm-106-disk-3,iothread=1,size=1G
> vmgenid: 0a1d8751-5e02-449d-977e-c0160e900231

Before the change:

> root@pve8a1 ~ # grep VmRSS /proc/$(cat /var/run/qemu-server/106.pid)/status
> VmRSS:	  370948 kB
> root@pve8a1 ~ # vzdump 106 --storage pbs
> (...)
> INFO: Backup job finished successfully
> root@pve8a1 ~ # grep VmRSS /proc/$(cat /var/run/qemu-server/106.pid)/status
> VmRSS:	 2114964 kB

After the change:

> root@pve8a1 ~ # grep VmRSS /proc/$(cat /var/run/qemu-server/106.pid)/status
> VmRSS:	  398788 kB
> root@pve8a1 ~ # vzdump 106 --storage pbs
> (...)
> INFO: Backup job finished successfully
> root@pve8a1 ~ # grep VmRSS /proc/$(cat /var/run/qemu-server/106.pid)/status
> VmRSS:	  424356 kB

[0]: https://forum.proxmox.com/threads/131339/

Co-diagnosed-by: Friedrich Weber <f.weber@proxmox.com>
Co-diagnosed-by: Dominik Csapak <d.csapak@proxmox.com>
Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
Acked-by: Wolfgang Bumiller <w.bumiller@proxmox.com>
This commit is contained in:
Fiona Ebner 2023-08-14 10:53:19 +02:00
parent c36e3f9d17
commit 5f9cb29c3a
2 changed files with 20 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

23
debian/patches/pve/0030-PVE-Backup-Proxmox-backup-patches-for-QEMU.patch vendored
View File

@ -79,7 +79,8 @@ Signed-off-by: Wolfgang Bumiller <w.bumiller@proxmox.com>
adapt for new job lock mechanism replacing AioContext locks
adapt to QAPI changes
improve canceling
allow passing max-workers setting]
allow passing max-workers setting
use malloc_trim after backup]
Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
---
block/meson.build | 5 +
@ -92,11 +93,11 @@ Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
monitor/hmp-cmds.c | 72 +++
proxmox-backup-client.c | 146 +++++
proxmox-backup-client.h | 60 ++
pve-backup.c | 1097 ++++++++++++++++++++++++++++++++
pve-backup.c | 1109 ++++++++++++++++++++++++++++++++
qapi/block-core.json | 226 +++++++
qapi/common.json | 13 +
qapi/machine.json | 15 +-
14 files changed, 1711 insertions(+), 13 deletions(-)
14 files changed, 1723 insertions(+), 13 deletions(-)
create mode 100644 proxmox-backup-client.c
create mode 100644 proxmox-backup-client.h
create mode 100644 pve-backup.c
@ -587,10 +588,10 @@ index 0000000000..8cbf645b2c
+#endif /* PROXMOX_BACKUP_CLIENT_H */
diff --git a/pve-backup.c b/pve-backup.c
new file mode 100644
index 0000000000..dd72ee0ed6
index 0000000000..10ca8a0b1d
--- /dev/null
+++ b/pve-backup.c
@@ -0,0 +1,1097 @@
@@ -0,0 +1,1109 @@
+#include "proxmox-backup-client.h"
+#include "vma.h"
+
@ -605,6 +606,10 @@ index 0000000000..dd72ee0ed6
+#include "qapi/qmp/qerror.h"
+#include "qemu/cutils.h"
+
+#if defined(CONFIG_MALLOC_TRIM)
+#include <malloc.h>
+#endif
+
+#include <proxmox-backup-qemu.h>
+
+/* PVE backup state and related function */
@ -869,6 +874,14 @@ index 0000000000..dd72ee0ed6
+ backup_state.stat.end_time = time(NULL);
+ backup_state.stat.finishing = false;
+ qemu_mutex_unlock(&backup_state.stat.lock);
+
+#if defined(CONFIG_MALLOC_TRIM)
+ /*
+ * Try to reclaim memory for buffers (and, in case of PBS, Rust futures), etc.
+ * Won't happen by default if there is fragmentation.
+ */
+ malloc_trim(4 * 1024 * 1024);
+#endif
+}
+
+static void coroutine_fn pvebackup_co_complete_stream(void *opaque)

4
debian/patches/pve/0034-PVE-Migrate-dirty-bitmap-state-via-savevm.patch vendored
View File

@ -175,10 +175,10 @@ index 0000000000..887e998b9e
+ NULL);
+}
diff --git a/pve-backup.c b/pve-backup.c
index dd72ee0ed6..cb5312fff3 100644
index 10ca8a0b1d..0a5ce2cab8 100644
--- a/pve-backup.c
+++ b/pve-backup.c
@@ -1090,6 +1090,7 @@ ProxmoxSupportStatus *qmp_query_proxmox_support(Error **errp)
@@ -1102,6 +1102,7 @@ ProxmoxSupportStatus *qmp_query_proxmox_support(Error **errp)
ret->pbs_library_version = g_strdup(proxmox_backup_qemu_version());
ret->pbs_dirty_bitmap = true;
ret->pbs_dirty_bitmap_savevm = true;