pve-qemu-qoup/debian/patches/pve/0045-block-copy-before-write-support-unligned-snapshot-di.patch

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implement support for backup fleecing Excerpt from Fiona's v3 cover-letter [0]: When a backup for a VM is started, QEMU will install a "copy-before-write" filter in its block layer. This filter ensures that upon new guest writes, old data still needed for the backup is sent to the backup target first. The guest write blocks until this operation is finished so guest IO to not-yet-backed-up sectors will be limited by the speed of the backup target. With backup fleecing, such old data is cached in a fleecing image rather than sent directly to the backup target. This can help guest IO performance and even prevent hangs in certain scenarios, at the cost of requiring more storage space. With this series it will be possible to enable backup-fleecing via e.g. `vzdump 123 --fleecing enabled=1,storage=local-lvm` with fleecing images created on the storage `local-lvm`. The fleecing storage should be a fast local storage which supports thin-provisioning and discard. If the storage supports qcow2, that is used as the fleecing image format. If the underlying file system does not support discard, with qcow2 and preallocation=off, at least already allocated parts of the image can be re-used later. Fleecing images are created by qemu-server via pve-storage and attached to QEMU before the backup starts, and cleaned up after the backup finished or failed. The naming schema for fleecing images is 'vm-ID-fleece-N(.FORMAT)'. The allocated images are recorded in the guest configuration, so that even after a hard failure, clean-up can be re-attempted. While not too bad, it's a non-trivial amount of code and I'm not 100% sure about the cost-benefit, so sending those as RFC. The fleecing image needs to be the exact same size as the source, but luckily, an explicit size can be specified when attaching a raw image to QEMU so there are no size issues when using storages that have coarser allocation/round up. For qcow2, it seems that virtual size can be nearly arbitrary (i.e. modulo 512 byte granularity) during allocation. [0]: https://lists.proxmox.com/pipermail/pve-devel/2024-April/062815.html Originally-by: Fiona Ebner <f.ebner@proxmox.com> Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
2024-04-11 18:38:26 +03:00
From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Date: Thu, 11 Apr 2024 11:29:23 +0200
Subject: [PATCH] block/copy-before-write: support unligned snapshot-discard
First thing that crashes on unligned access here is
bdrv_reset_dirty_bitmap(). Correct way is to align-down the
snapshot-discard request.
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
---
block/copy-before-write.c | 16 +++++++++++++---
1 file changed, 13 insertions(+), 3 deletions(-)
diff --git a/block/copy-before-write.c b/block/copy-before-write.c
index 5a9456d426..c0e70669a2 100644
implement support for backup fleecing Excerpt from Fiona's v3 cover-letter [0]: When a backup for a VM is started, QEMU will install a "copy-before-write" filter in its block layer. This filter ensures that upon new guest writes, old data still needed for the backup is sent to the backup target first. The guest write blocks until this operation is finished so guest IO to not-yet-backed-up sectors will be limited by the speed of the backup target. With backup fleecing, such old data is cached in a fleecing image rather than sent directly to the backup target. This can help guest IO performance and even prevent hangs in certain scenarios, at the cost of requiring more storage space. With this series it will be possible to enable backup-fleecing via e.g. `vzdump 123 --fleecing enabled=1,storage=local-lvm` with fleecing images created on the storage `local-lvm`. The fleecing storage should be a fast local storage which supports thin-provisioning and discard. If the storage supports qcow2, that is used as the fleecing image format. If the underlying file system does not support discard, with qcow2 and preallocation=off, at least already allocated parts of the image can be re-used later. Fleecing images are created by qemu-server via pve-storage and attached to QEMU before the backup starts, and cleaned up after the backup finished or failed. The naming schema for fleecing images is 'vm-ID-fleece-N(.FORMAT)'. The allocated images are recorded in the guest configuration, so that even after a hard failure, clean-up can be re-attempted. While not too bad, it's a non-trivial amount of code and I'm not 100% sure about the cost-benefit, so sending those as RFC. The fleecing image needs to be the exact same size as the source, but luckily, an explicit size can be specified when attaching a raw image to QEMU so there are no size issues when using storages that have coarser allocation/round up. For qcow2, it seems that virtual size can be nearly arbitrary (i.e. modulo 512 byte granularity) during allocation. [0]: https://lists.proxmox.com/pipermail/pve-devel/2024-April/062815.html Originally-by: Fiona Ebner <f.ebner@proxmox.com> Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
2024-04-11 18:38:26 +03:00
--- a/block/copy-before-write.c
+++ b/block/copy-before-write.c
@@ -325,14 +325,24 @@ static int coroutine_fn GRAPH_RDLOCK
cbw_co_pdiscard_snapshot(BlockDriverState *bs, int64_t offset, int64_t bytes)
{
BDRVCopyBeforeWriteState *s = bs->opaque;
+ uint32_t cluster_size = block_copy_cluster_size(s->bcs);
+ int64_t aligned_offset = QEMU_ALIGN_UP(offset, cluster_size);
+ int64_t aligned_end = QEMU_ALIGN_DOWN(offset + bytes, cluster_size);
+ int64_t aligned_bytes;
+
+ if (aligned_end <= aligned_offset) {
+ return 0;
+ }
+ aligned_bytes = aligned_end - aligned_offset;
WITH_QEMU_LOCK_GUARD(&s->lock) {
- bdrv_reset_dirty_bitmap(s->access_bitmap, offset, bytes);
+ bdrv_reset_dirty_bitmap(s->access_bitmap, aligned_offset,
+ aligned_bytes);
}
- block_copy_reset(s->bcs, offset, bytes);
+ block_copy_reset(s->bcs, aligned_offset, aligned_bytes);
- return bdrv_co_pdiscard(s->target, offset, bytes);
+ return bdrv_co_pdiscard(s->target, aligned_offset, aligned_bytes);
}
update submodule and patches to QEMU 8.2.2 This version includes both the AioContext lock and the block graph lock, so there might be some deadlocks lurking. It's not possible to disable the block graph lock like was done in QEMU 8.1, because there are no changes like the function bdrv_schedule_unref() that require it. QEMU 9.0 will finally get rid of the AioContext locking. During live-restore with a VirtIO SCSI drive with iothread there is a known racy deadlock related to the AioContext lock. Not new [1], but not sure if more likely now. Should be fixed in QEMU 9.0. The block graph lock comes with annotations that can be checked by clang's TSA. This required changes to the block drivers, i.e. alloc-track, pbs, zeroinit as well as taking the appropriate locks in pve-backup, savevm-async, vma-reader. Local variable shadowing is prohibited via a compiler flag now, required slight adaptation in vma.c. Major changes only affect alloc-track: * It is not possible to call a generated co-wrapper like bdrv_get_info() while holding the block graph lock exclusively [0], which does happen during initialization of alloc-track when the backing hd is set and the refresh_limits driver callback is invoked. The bdrv_get_info() call to get the cluster size is moved to directly after opening the file child in track_open(). The important thing is that at least the request alignment for the write target is used, because then the RMW cycle in bdrv_pwritev will gather enough data from the backing file. Partial cluster allocations in the target are not a fundamental issue, because the driver returns its allocation status based on the bitmap, so any other data that maps to the same cluster will still be copied later by a stream job (or during writes to that cluster). * Replacing the node cannot be done in the track_co_change_backing_file() callback, because it is a coroutine and cannot hold the block graph lock exclusively. So it is moved to the stream job itself with the auto-remove option not having an effect anymore (qemu-server would always set it anyways). In the future, there could either be a special option for the stream job, or maybe the upcoming blockdev-replace QMP command can be used. Replacing the backing child is actually already done in the stream job, so no need to do it in the track_co_change_backing_file() callback. It also cannot be called from a coroutine. Looking at the implementation in the qcow2 driver, it doesn't seem to be intended to change the backing child itself, just update driver-internal state. Other changes: * alloc-track: Error out early when used without auto-remove. Since replacing the node now happens in the stream job, where the option cannot be read from (it's internal to the driver), it will always be treated as 'on'. Makes sure to have users beside qemu-server notice the change (should they even exist). The option can be fully dropped in the future while adding a version guard in qemu-server. * alloc-track: Avoid seemingly superfluous child permission update. Doesn't seem necessary nowadays (maybe after commit "alloc-track: fix deadlock during drop" where the dropping is not rescheduled and delayed anymore or some upstream change). Replacing the block node will already update the permissions of the new node (which was the file child before). Should there really be some issue, instead of having a drop state, this could also be just based off the fact whether there is still a backing child. Dumping the cumulative (shared) permissions for the BDS with a debug print yields the same values after this patch and with QEMU 8.1, namely 3 and 5. * PBS block driver: compile unconditionally. Proxmox VE always needs it and something in the build process changed to make it not enabled by default. Probably would need to move the build option to meson otherwise. * backup: job unreferencing during cleanup needs to happen outside of coroutine, so it was moved to before invoking the clean * mirror: Cherry-pick stable fix to avoid potential deadlock. * savevm-async: migrate_init now can fail, so propagate potential error. * savevm-async: compression counters are not accessible outside migration/ram-compress now, so drop code that prophylactically set it to zero. [0]: https://lore.kernel.org/qemu-devel/220be383-3b0d-4938-b584-69ad214e5d5d@proxmox.com/ [1]: https://lore.kernel.org/qemu-devel/e13b488e-bf13-44f2-acca-e724d14f43fd@proxmox.com/ Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
2024-04-25 18:21:28 +03:00
static void GRAPH_RDLOCK cbw_refresh_filename(BlockDriverState *bs)