[pbs-devel] [PATCH pve-qemu v3] add alloc-track block driver patch

Stefan Reiter s.reiter at proxmox.com
Mon Mar 15 16:41:24 CET 2021


See added patches for more info, overview:
0044: slightly increase PBS performance by reducing allocations
0045: slightly increase block-stream performance for Ceph
0046: don't crash with block-stream on RBD
0047: add alloc-track driver for live restore

Signed-off-by: Stefan Reiter <s.reiter at proxmox.com>
---

v3:
* improve track_drop as discussed by @Wolfgang, both on and off list
  (DropState, additional bdrv_ref/unref)

track_drop is certainly not beautiful, but it works reliably in our use-case...

 ...st-path-reads-without-allocation-if-.patch |  52 +++
 ...PVE-block-stream-increase-chunk-size.patch |  23 ++
 ...accept-NULL-qiov-in-bdrv_pad_request.patch |  42 ++
 .../0047-block-add-alloc-track-driver.patch   | 391 ++++++++++++++++++
 debian/patches/series                         |   4 +
 5 files changed, 512 insertions(+)
 create mode 100644 debian/patches/pve/0044-PVE-block-pbs-fast-path-reads-without-allocation-if-.patch
 create mode 100644 debian/patches/pve/0045-PVE-block-stream-increase-chunk-size.patch
 create mode 100644 debian/patches/pve/0046-block-io-accept-NULL-qiov-in-bdrv_pad_request.patch
 create mode 100644 debian/patches/pve/0047-block-add-alloc-track-driver.patch

diff --git a/debian/patches/pve/0044-PVE-block-pbs-fast-path-reads-without-allocation-if-.patch b/debian/patches/pve/0044-PVE-block-pbs-fast-path-reads-without-allocation-if-.patch
new file mode 100644
index 0000000..a85ebc2
--- /dev/null
+++ b/debian/patches/pve/0044-PVE-block-pbs-fast-path-reads-without-allocation-if-.patch
@@ -0,0 +1,52 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Stefan Reiter <s.reiter at proxmox.com>
+Date: Wed, 9 Dec 2020 11:46:57 +0100
+Subject: [PATCH] PVE: block/pbs: fast-path reads without allocation if
+ possible
+
+...and switch over to g_malloc/g_free while at it to align with other
+QEMU code.
+
+Tracing shows the fast-path is taken almost all the time, though not
+100% so the slow one is still necessary.
+
+Signed-off-by: Stefan Reiter <s.reiter at proxmox.com>
+---
+ block/pbs.c | 17 ++++++++++++++---
+ 1 file changed, 14 insertions(+), 3 deletions(-)
+
+diff --git a/block/pbs.c b/block/pbs.c
+index 1481a2bfd1..fbf0d8d845 100644
+--- a/block/pbs.c
++++ b/block/pbs.c
+@@ -200,7 +200,16 @@ static coroutine_fn int pbs_co_preadv(BlockDriverState *bs,
+     BDRVPBSState *s = bs->opaque;
+     int ret;
+     char *pbs_error = NULL;
+-    uint8_t *buf = malloc(bytes);
++    uint8_t *buf;
++    bool inline_buf = true;
++
++    /* for single-buffer IO vectors we can fast-path the write directly to it */
++    if (qiov->niov == 1 && qiov->iov->iov_len >= bytes) {
++        buf = qiov->iov->iov_base;
++    } else {
++        inline_buf = false;
++        buf = g_malloc(bytes);
++    }
+ 
+     ReadCallbackData rcb = {
+         .co = qemu_coroutine_self(),
+@@ -218,8 +227,10 @@ static coroutine_fn int pbs_co_preadv(BlockDriverState *bs,
+         return -EIO;
+     }
+ 
+-    qemu_iovec_from_buf(qiov, 0, buf, bytes);
+-    free(buf);
++    if (!inline_buf) {
++        qemu_iovec_from_buf(qiov, 0, buf, bytes);
++        g_free(buf);
++    }
+ 
+     return ret;
+ }
diff --git a/debian/patches/pve/0045-PVE-block-stream-increase-chunk-size.patch b/debian/patches/pve/0045-PVE-block-stream-increase-chunk-size.patch
new file mode 100644
index 0000000..601f8c7
--- /dev/null
+++ b/debian/patches/pve/0045-PVE-block-stream-increase-chunk-size.patch
@@ -0,0 +1,23 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Stefan Reiter <s.reiter at proxmox.com>
+Date: Tue, 2 Mar 2021 16:34:28 +0100
+Subject: [PATCH] PVE: block/stream: increase chunk size
+
+Ceph favors bigger chunks, so increase to 4M.
+---
+ block/stream.c | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/block/stream.c b/block/stream.c
+index 236384f2f7..a5371420e3 100644
+--- a/block/stream.c
++++ b/block/stream.c
+@@ -26,7 +26,7 @@ enum {
+      * large enough to process multiple clusters in a single call, so
+      * that populating contiguous regions of the image is efficient.
+      */
+-    STREAM_CHUNK = 512 * 1024, /* in bytes */
++    STREAM_CHUNK = 4 * 1024 * 1024, /* in bytes */
+ };
+ 
+ typedef struct StreamBlockJob {
diff --git a/debian/patches/pve/0046-block-io-accept-NULL-qiov-in-bdrv_pad_request.patch b/debian/patches/pve/0046-block-io-accept-NULL-qiov-in-bdrv_pad_request.patch
new file mode 100644
index 0000000..e40fa2e
--- /dev/null
+++ b/debian/patches/pve/0046-block-io-accept-NULL-qiov-in-bdrv_pad_request.patch
@@ -0,0 +1,42 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Stefan Reiter <s.reiter at proxmox.com>
+Date: Tue, 2 Mar 2021 16:11:54 +0100
+Subject: [PATCH] block/io: accept NULL qiov in bdrv_pad_request
+
+Some operations, e.g. block-stream, perform reads while discarding the
+results (only copy-on-read matters). In this case they will pass NULL as
+the target QEMUIOVector, which will however trip bdrv_pad_request, since
+it wants to extend its passed vector.
+
+Simply check for NULL and do nothing, there's no reason to pad the
+target if it will be discarded anyway.
+---
+ block/io.c | 13 ++++++++-----
+ 1 file changed, 8 insertions(+), 5 deletions(-)
+
+diff --git a/block/io.c b/block/io.c
+index ec5e152bb7..08dee005ec 100644
+--- a/block/io.c
++++ b/block/io.c
+@@ -1613,13 +1613,16 @@ static bool bdrv_pad_request(BlockDriverState *bs,
+         return false;
+     }
+ 
+-    qemu_iovec_init_extended(&pad->local_qiov, pad->buf, pad->head,
+-                             *qiov, *qiov_offset, *bytes,
+-                             pad->buf + pad->buf_len - pad->tail, pad->tail);
++    if (*qiov) {
++        qemu_iovec_init_extended(&pad->local_qiov, pad->buf, pad->head,
++                                *qiov, *qiov_offset, *bytes,
++                                pad->buf + pad->buf_len - pad->tail, pad->tail);
++        *qiov = &pad->local_qiov;
++        *qiov_offset = 0;
++    }
++
+     *bytes += pad->head + pad->tail;
+     *offset -= pad->head;
+-    *qiov = &pad->local_qiov;
+-    *qiov_offset = 0;
+ 
+     return true;
+ }
diff --git a/debian/patches/pve/0047-block-add-alloc-track-driver.patch b/debian/patches/pve/0047-block-add-alloc-track-driver.patch
new file mode 100644
index 0000000..db46371
--- /dev/null
+++ b/debian/patches/pve/0047-block-add-alloc-track-driver.patch
@@ -0,0 +1,391 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Stefan Reiter <s.reiter at proxmox.com>
+Date: Mon, 7 Dec 2020 15:21:03 +0100
+Subject: [PATCH] block: add alloc-track driver
+
+Add a new filter node 'alloc-track', which seperates reads and writes to
+different children, thus allowing to put a backing image behind any
+blockdev (regardless of driver support). Since we can't detect any
+pre-allocated blocks, we can only track new writes, hence the write
+target ('file') for this node must always be empty.
+
+Intended use case is for live restoring, i.e. add a backup image as a
+block device into a VM, then put an alloc-track on the restore target
+and set the backup as backing. With this, one can use a regular
+'block-stream' to restore the image, while the VM can already run in the
+background. Copy-on-read will help make progress as the VM reads as
+well.
+
+This only worked if the target supports backing images, so up until now
+only for qcow2, with alloc-track any driver for the target can be used.
+
+If 'auto-remove' is set, alloc-track will automatically detach itself
+once the backing image is removed. It will be replaced by 'file'.
+
+Signed-off-by: Stefan Reiter <s.reiter at proxmox.com>
+---
+ block/alloc-track.c | 342 ++++++++++++++++++++++++++++++++++++++++++++
+ block/meson.build   |   1 +
+ 2 files changed, 343 insertions(+)
+ create mode 100644 block/alloc-track.c
+
+diff --git a/block/alloc-track.c b/block/alloc-track.c
+new file mode 100644
+index 0000000000..b579380279
+--- /dev/null
++++ b/block/alloc-track.c
+@@ -0,0 +1,342 @@
++/*
++ * Node to allow backing images to be applied to any node. Assumes a blank
++ * image to begin with, only new writes are tracked as allocated, thus this
++ * must never be put on a node that already contains data.
++ *
++ * Copyright (c) 2020 Proxmox Server Solutions GmbH
++ * Copyright (c) 2020 Stefan Reiter <s.reiter at proxmox.com>
++ *
++ * This work is licensed under the terms of the GNU GPL, version 2 or later.
++ * See the COPYING file in the top-level directory.
++ */
++
++#include "qemu/osdep.h"
++#include "qapi/error.h"
++#include "block/block_int.h"
++#include "qapi/qmp/qdict.h"
++#include "qapi/qmp/qstring.h"
++#include "qemu/cutils.h"
++#include "qemu/option.h"
++#include "qemu/module.h"
++#include "sysemu/block-backend.h"
++
++#define TRACK_OPT_AUTO_REMOVE "auto-remove"
++
++typedef enum DropState {
++    DropNone,
++    DropRequested,
++    DropInProgress,
++} DropState;
++
++typedef struct {
++    BdrvDirtyBitmap *bitmap;
++    DropState drop_state;
++    bool auto_remove;
++} BDRVAllocTrackState;
++
++static QemuOptsList runtime_opts = {
++    .name = "alloc-track",
++    .head = QTAILQ_HEAD_INITIALIZER(runtime_opts.head),
++    .desc = {
++        {
++            .name = TRACK_OPT_AUTO_REMOVE,
++            .type = QEMU_OPT_BOOL,
++            .help = "automatically replace this node with 'file' when 'backing'"
++                    "is detached",
++        },
++        { /* end of list */ }
++    },
++};
++
++static void track_refresh_limits(BlockDriverState *bs, Error **errp)
++{
++    BlockDriverInfo bdi;
++
++    if (!bs->file) {
++        return;
++    }
++
++    /* always use alignment from underlying write device so RMW cycle for
++     * bdrv_pwritev reads data from our backing via track_co_preadv (no partial
++     * cluster allocation in 'file') */
++    bdrv_get_info(bs->file->bs, &bdi);
++    bs->bl.request_alignment = MAX(bs->file->bs->bl.request_alignment,
++                                   MAX(bdi.cluster_size, BDRV_SECTOR_SIZE));
++}
++
++static int track_open(BlockDriverState *bs, QDict *options, int flags,
++                      Error **errp)
++{
++    BDRVAllocTrackState *s = bs->opaque;
++    QemuOpts *opts;
++    Error *local_err = NULL;
++    int ret = 0;
++
++    opts = qemu_opts_create(&runtime_opts, NULL, 0, &error_abort);
++    qemu_opts_absorb_qdict(opts, options, &local_err);
++    if (local_err) {
++        error_propagate(errp, local_err);
++        ret = -EINVAL;
++        goto fail;
++    }
++
++    s->auto_remove = qemu_opt_get_bool(opts, TRACK_OPT_AUTO_REMOVE, false);
++
++    /* open the target (write) node, backing will be attached by block layer */
++    bs->file = bdrv_open_child(NULL, options, "file", bs, &child_of_bds,
++                               BDRV_CHILD_DATA | BDRV_CHILD_METADATA, false,
++                               &local_err);
++    if (local_err) {
++        ret = -EINVAL;
++        error_propagate(errp, local_err);
++        goto fail;
++    }
++
++    track_refresh_limits(bs, errp);
++    uint64_t gran = bs->bl.request_alignment;
++    s->bitmap = bdrv_create_dirty_bitmap(bs->file->bs, gran, NULL, &local_err);
++    if (local_err) {
++        ret = -EIO;
++        error_propagate(errp, local_err);
++        goto fail;
++    }
++
++    s->drop_state = DropNone;
++
++fail:
++    if (ret < 0) {
++        bdrv_unref_child(bs, bs->file);
++        if (s->bitmap) {
++            bdrv_release_dirty_bitmap(s->bitmap);
++        }
++    }
++    qemu_opts_del(opts);
++    return ret;
++}
++
++static void track_close(BlockDriverState *bs)
++{
++    BDRVAllocTrackState *s = bs->opaque;
++    if (s->bitmap) {
++        bdrv_release_dirty_bitmap(s->bitmap);
++    }
++}
++
++static int64_t track_getlength(BlockDriverState *bs)
++{
++    return bdrv_getlength(bs->file->bs);
++}
++
++static int coroutine_fn track_co_preadv(BlockDriverState *bs,
++    uint64_t offset, uint64_t bytes, QEMUIOVector *qiov, int flags)
++{
++    BDRVAllocTrackState *s = bs->opaque;
++    QEMUIOVector local_qiov;
++    int ret;
++
++    /* 'cur_offset' is relative to 'offset', 'local_offset' to image start */
++    uint64_t cur_offset, local_offset;
++    int64_t local_bytes;
++    bool alloc;
++
++    /* a read request can span multiple granularity-sized chunks, and can thus
++     * contain blocks with different allocation status - we could just iterate
++     * granularity-wise, but for better performance use bdrv_dirty_bitmap_next_X
++     * to find the next flip and consider everything up to that in one go */
++    for (cur_offset = 0; cur_offset < bytes; cur_offset += local_bytes) {
++        local_offset = offset + cur_offset;
++        alloc = bdrv_dirty_bitmap_get(s->bitmap, local_offset);
++        if (alloc) {
++            local_bytes = bdrv_dirty_bitmap_next_zero(s->bitmap, local_offset,
++                                                      bytes - cur_offset);
++        } else {
++            local_bytes = bdrv_dirty_bitmap_next_dirty(s->bitmap, local_offset,
++                                                       bytes - cur_offset);
++        }
++
++        /* _bitmap_next_X return is -1 if no end found within limit, otherwise
++         * offset of next flip (to start of image) */
++        local_bytes = local_bytes < 0 ?
++            bytes - cur_offset :
++            local_bytes - local_offset;
++
++        qemu_iovec_init_slice(&local_qiov, qiov, cur_offset, local_bytes);
++
++        if (alloc) {
++            ret = bdrv_co_preadv(bs->file, local_offset, local_bytes,
++                                 &local_qiov, flags);
++        } else if (bs->backing) {
++            ret = bdrv_co_preadv(bs->backing, local_offset, local_bytes,
++                                 &local_qiov, flags);
++        } else {
++            ret = qemu_iovec_memset(&local_qiov, cur_offset, 0, local_bytes);
++        }
++
++        if (ret != 0) {
++            break;
++        }
++    }
++
++    return ret;
++}
++
++static int coroutine_fn track_co_pwritev(BlockDriverState *bs,
++    uint64_t offset, uint64_t bytes, QEMUIOVector *qiov, int flags)
++{
++    return bdrv_co_pwritev(bs->file, offset, bytes, qiov, flags);
++}
++
++static int coroutine_fn track_co_pwrite_zeroes(BlockDriverState *bs,
++    int64_t offset, int count, BdrvRequestFlags flags)
++{
++    return bdrv_pwrite_zeroes(bs->file, offset, count, flags);
++}
++
++static int coroutine_fn track_co_pdiscard(BlockDriverState *bs,
++    int64_t offset, int count)
++{
++    return bdrv_co_pdiscard(bs->file, offset, count);
++}
++
++static coroutine_fn int track_co_flush(BlockDriverState *bs)
++{
++    return bdrv_co_flush(bs->file->bs);
++}
++
++static int coroutine_fn track_co_block_status(BlockDriverState *bs,
++                                              bool want_zero,
++                                              int64_t offset,
++                                              int64_t bytes,
++                                              int64_t *pnum,
++                                              int64_t *map,
++                                              BlockDriverState **file)
++{
++    BDRVAllocTrackState *s = bs->opaque;
++
++    bool alloc = bdrv_dirty_bitmap_get(s->bitmap, offset);
++    int64_t next_flipped;
++    if (alloc) {
++        next_flipped = bdrv_dirty_bitmap_next_zero(s->bitmap, offset, bytes);
++    } else {
++        next_flipped = bdrv_dirty_bitmap_next_dirty(s->bitmap, offset, bytes);
++    }
++
++    /* in case not the entire region has the same state, we need to set pnum to
++     * indicate for how many bytes our result is valid */
++    *pnum = next_flipped == -1 ? bytes : next_flipped - offset;
++    *map = offset;
++
++    if (alloc) {
++        *file = bs->file->bs;
++        return BDRV_BLOCK_RAW | BDRV_BLOCK_OFFSET_VALID;
++    } else if (bs->backing) {
++        *file = bs->backing->bs;
++    }
++    return 0;
++}
++
++static void track_child_perm(BlockDriverState *bs, BdrvChild *c,
++                             BdrvChildRole role, BlockReopenQueue *reopen_queue,
++                             uint64_t perm, uint64_t shared,
++                             uint64_t *nperm, uint64_t *nshared)
++{
++    BDRVAllocTrackState *s = bs->opaque;
++
++    *nshared = BLK_PERM_ALL;
++
++    /* in case we're currently dropping ourselves, claim to not use any
++     * permissions at all - which is fine, since from this point on we will
++     * never issue a read or write anymore */
++    if (s->drop_state == DropInProgress) {
++        *nperm = 0;
++        return;
++    }
++
++    if (role & BDRV_CHILD_DATA) {
++        *nperm = perm & DEFAULT_PERM_PASSTHROUGH;
++    } else {
++        /* 'backing' is also a child of our BDS, but we don't expect it to be
++         * writeable, so we only forward 'consistent read' */
++        *nperm = perm & BLK_PERM_CONSISTENT_READ;
++    }
++}
++
++static void track_drop(void *opaque)
++{
++    BlockDriverState *bs = (BlockDriverState*)opaque;
++    BlockDriverState *file = bs->file->bs;
++    BDRVAllocTrackState *s = bs->opaque;
++
++    assert(file);
++
++    /* we rely on the fact that we're not used anywhere else, so let's wait
++     * until we're only used once - in the drive connected to the guest (and one
++     * ref is held by bdrv_ref in track_change_backing_file) */
++    if (bs->refcnt > 2) {
++        aio_bh_schedule_oneshot(qemu_get_aio_context(), track_drop, opaque);
++        return;
++    }
++
++    /* we do not need a bdrv_drained_end, since this is applied only to the node
++     * which gets removed by bdrv_replace_node */
++    bdrv_drained_begin(bs);
++
++    /* now that we're drained, we can safely set 'DropInProgress' */
++    s->drop_state = DropInProgress;
++    bdrv_child_refresh_perms(bs, bs->file, &error_abort);
++
++    bdrv_replace_node(bs, file, &error_abort);
++    bdrv_unref(bs);
++}
++
++static int track_change_backing_file(BlockDriverState *bs,
++                                     const char *backing_file,
++                                     const char *backing_fmt)
++{
++    BDRVAllocTrackState *s = bs->opaque;
++    if (s->auto_remove && s->drop_state == DropNone &&
++        backing_file == NULL && backing_fmt == NULL)
++    {
++        /* backing file has been disconnected, there's no longer any use for
++         * this node, so let's remove ourselves from the block graph - we need
++         * to schedule this for later however, since when this function is
++         * called, the blockjob modifying us is probably not done yet and has a
++         * blocker on 'bs' */
++        s->drop_state = DropRequested;
++        bdrv_ref(bs);
++        aio_bh_schedule_oneshot(qemu_get_aio_context(), track_drop, (void*)bs);
++    }
++
++    return 0;
++}
++
++static BlockDriver bdrv_alloc_track = {
++    .format_name                      = "alloc-track",
++    .instance_size                    = sizeof(BDRVAllocTrackState),
++
++    .bdrv_file_open                   = track_open,
++    .bdrv_close                       = track_close,
++    .bdrv_getlength                   = track_getlength,
++    .bdrv_child_perm                  = track_child_perm,
++    .bdrv_refresh_limits              = track_refresh_limits,
++
++    .bdrv_co_pwrite_zeroes            = track_co_pwrite_zeroes,
++    .bdrv_co_pwritev                  = track_co_pwritev,
++    .bdrv_co_preadv                   = track_co_preadv,
++    .bdrv_co_pdiscard                 = track_co_pdiscard,
++
++    .bdrv_co_flush                    = track_co_flush,
++    .bdrv_co_flush_to_disk            = track_co_flush,
++
++    .supports_backing                 = true,
++
++    .bdrv_co_block_status             = track_co_block_status,
++    .bdrv_change_backing_file         = track_change_backing_file,
++};
++
++static void bdrv_alloc_track_init(void)
++{
++    bdrv_register(&bdrv_alloc_track);
++}
++
++block_init(bdrv_alloc_track_init);
+diff --git a/block/meson.build b/block/meson.build
+index a070060e53..e387990764 100644
+--- a/block/meson.build
++++ b/block/meson.build
+@@ -2,6 +2,7 @@ block_ss.add(genh)
+ block_ss.add(files(
+   'accounting.c',
+   'aio_task.c',
++  'alloc-track.c',
+   'amend.c',
+   'backup.c',
+   'backup-dump.c',
diff --git a/debian/patches/series b/debian/patches/series
index f29a15d..da4f9c7 100644
--- a/debian/patches/series
+++ b/debian/patches/series
@@ -56,3 +56,7 @@ pve/0040-migration-block-dirty-bitmap-migrate-other-bitmaps-e.patch
 pve/0041-PVE-fall-back-to-open-iscsi-initiatorname.patch
 pve/0042-PVE-Use-coroutine-QMP-for-backup-cancel_backup.patch
 pve/0043-PBS-add-master-key-support.patch
+pve/0044-PVE-block-pbs-fast-path-reads-without-allocation-if-.patch
+pve/0045-PVE-block-stream-increase-chunk-size.patch
+pve/0046-block-io-accept-NULL-qiov-in-bdrv_pad_request.patch
+pve/0047-block-add-alloc-track-driver.patch
-- 
2.20.1






More information about the pbs-devel mailing list