block/iscsi: allow caching of the allocation map
until now the allocation map was used only as a hint if a cluster
is allocated or not. If a block was not allocated (or Qemu had
no info about the allocation status) a get_block_status call was
issued to check the allocation status and possibly avoid
a subsequent read of unallocated sectors. If a block known to be
allocated the get_block_status call was omitted. In the other case
a get_block_status call was issued before every read to avoid
the necessity for a consistent allocation map. To avoid the
potential overhead of calling get_block_status for each and
every read request this took only place for the bigger requests.
This patch enhances this mechanism to cache the allocation
status and avoid calling get_block_status for blocks where
the allocation status has been queried before. This allows
for bypassing the read request even for smaller requests and
additionally omits calling get_block_status for known to be
unallocated blocks.
Signed-off-by: Peter Lieven <pl@kamp.de>
Message-Id: <1468831940-15556-3-git-send-email-pl@kamp.de>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/block/iscsi.c b/block/iscsi.c
index 22330e1..129c3af 100644
--- a/block/iscsi.c
+++ b/block/iscsi.c
@@ -2,7 +2,7 @@
* QEMU Block driver for iSCSI images
*
* Copyright (c) 2010-2011 Ronnie Sahlberg <ronniesahlberg@gmail.com>
- * Copyright (c) 2012-2015 Peter Lieven <pl@kamp.de>
+ * Copyright (c) 2012-2016 Peter Lieven <pl@kamp.de>
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
@@ -61,7 +61,23 @@
struct scsi_inquiry_logical_block_provisioning lbp;
struct scsi_inquiry_block_limits bl;
unsigned char *zeroblock;
- unsigned long *allocationmap;
+ /* The allocmap tracks which clusters (pages) on the iSCSI target are
+ * allocated and which are not. In case a target returns zeros for
+ * unallocated pages (iscsilun->lprz) we can directly return zeros instead
+ * of reading zeros over the wire if a read request falls within an
+ * unallocated block. As there are 3 possible states we need 2 bitmaps to
+ * track. allocmap_valid keeps track if QEMU's information about a page is
+ * valid. allocmap tracks if a page is allocated or not. In case QEMU has no
+ * valid information about a page the corresponding allocmap entry should be
+ * switched to unallocated as well to force a new lookup of the allocation
+ * status as lookups are generally skipped if a page is suspect to be
+ * allocated. If a iSCSI target is opened with cache.direct = on the
+ * allocmap_valid does not exist turning all cached information invalid so
+ * that a fresh lookup is made for any page even if allocmap entry returns
+ * it's unallocated. */
+ unsigned long *allocmap;
+ unsigned long *allocmap_valid;
+ long allocmap_size;
int cluster_sectors;
bool use_16_for_rw;
bool write_protected;
@@ -422,39 +438,135 @@
iscsilun);
}
-static unsigned long *iscsi_allocationmap_init(IscsiLun *iscsilun)
+static void iscsi_allocmap_free(IscsiLun *iscsilun)
{
- return bitmap_try_new(DIV_ROUND_UP(sector_lun2qemu(iscsilun->num_blocks,
- iscsilun),
- iscsilun->cluster_sectors));
+ g_free(iscsilun->allocmap);
+ g_free(iscsilun->allocmap_valid);
+ iscsilun->allocmap = NULL;
+ iscsilun->allocmap_valid = NULL;
}
-static void iscsi_allocationmap_set(IscsiLun *iscsilun, int64_t sector_num,
- int nb_sectors)
+
+static int iscsi_allocmap_init(IscsiLun *iscsilun, int open_flags)
{
- int64_t cluster_num, nb_clusters;
- if (iscsilun->allocationmap == NULL) {
- return;
+ iscsi_allocmap_free(iscsilun);
+
+ iscsilun->allocmap_size =
+ DIV_ROUND_UP(sector_lun2qemu(iscsilun->num_blocks, iscsilun),
+ iscsilun->cluster_sectors);
+
+ iscsilun->allocmap = bitmap_try_new(iscsilun->allocmap_size);
+ if (!iscsilun->allocmap) {
+ return -ENOMEM;
}
- cluster_num = sector_num / iscsilun->cluster_sectors;
- nb_clusters = DIV_ROUND_UP(sector_num + nb_sectors,
- iscsilun->cluster_sectors) - cluster_num;
- bitmap_set(iscsilun->allocationmap, cluster_num, nb_clusters);
+
+ if (open_flags & BDRV_O_NOCACHE) {
+ /* in case that cache.direct = on all allocmap entries are
+ * treated as invalid to force a relookup of the block
+ * status on every read request */
+ return 0;
+ }
+
+ iscsilun->allocmap_valid = bitmap_try_new(iscsilun->allocmap_size);
+ if (!iscsilun->allocmap_valid) {
+ /* if we are under memory pressure free the allocmap as well */
+ iscsi_allocmap_free(iscsilun);
+ return -ENOMEM;
+ }
+
+ return 0;
}
-static void iscsi_allocationmap_clear(IscsiLun *iscsilun, int64_t sector_num,
- int nb_sectors)
+static void
+iscsi_allocmap_update(IscsiLun *iscsilun, int64_t sector_num,
+ int nb_sectors, bool allocated, bool valid)
{
- int64_t cluster_num, nb_clusters;
- if (iscsilun->allocationmap == NULL) {
+ int64_t cl_num_expanded, nb_cls_expanded, cl_num_shrunk, nb_cls_shrunk;
+
+ if (iscsilun->allocmap == NULL) {
return;
}
- cluster_num = DIV_ROUND_UP(sector_num, iscsilun->cluster_sectors);
- nb_clusters = (sector_num + nb_sectors) / iscsilun->cluster_sectors
- - cluster_num;
- if (nb_clusters > 0) {
- bitmap_clear(iscsilun->allocationmap, cluster_num, nb_clusters);
+ /* expand to entirely contain all affected clusters */
+ cl_num_expanded = sector_num / iscsilun->cluster_sectors;
+ nb_cls_expanded = DIV_ROUND_UP(sector_num + nb_sectors,
+ iscsilun->cluster_sectors) - cl_num_expanded;
+ /* shrink to touch only completely contained clusters */
+ cl_num_shrunk = DIV_ROUND_UP(sector_num, iscsilun->cluster_sectors);
+ nb_cls_shrunk = (sector_num + nb_sectors) / iscsilun->cluster_sectors
+ - cl_num_shrunk;
+ if (allocated) {
+ bitmap_set(iscsilun->allocmap, cl_num_expanded, nb_cls_expanded);
+ } else {
+ bitmap_clear(iscsilun->allocmap, cl_num_shrunk, nb_cls_shrunk);
}
+
+ if (iscsilun->allocmap_valid == NULL) {
+ return;
+ }
+ if (valid) {
+ bitmap_set(iscsilun->allocmap_valid, cl_num_shrunk, nb_cls_shrunk);
+ } else {
+ bitmap_clear(iscsilun->allocmap_valid, cl_num_expanded,
+ nb_cls_expanded);
+ }
+}
+
+static void
+iscsi_allocmap_set_allocated(IscsiLun *iscsilun, int64_t sector_num,
+ int nb_sectors)
+{
+ iscsi_allocmap_update(iscsilun, sector_num, nb_sectors, true, true);
+}
+
+static void
+iscsi_allocmap_set_unallocated(IscsiLun *iscsilun, int64_t sector_num,
+ int nb_sectors)
+{
+ /* Note: if cache.direct=on the fifth argument to iscsi_allocmap_update
+ * is ignored, so this will in effect be an iscsi_allocmap_set_invalid.
+ */
+ iscsi_allocmap_update(iscsilun, sector_num, nb_sectors, false, true);
+}
+
+static void iscsi_allocmap_set_invalid(IscsiLun *iscsilun, int64_t sector_num,
+ int nb_sectors)
+{
+ iscsi_allocmap_update(iscsilun, sector_num, nb_sectors, false, false);
+}
+
+static void iscsi_allocmap_invalidate(IscsiLun *iscsilun)
+{
+ if (iscsilun->allocmap) {
+ bitmap_zero(iscsilun->allocmap, iscsilun->allocmap_size);
+ }
+ if (iscsilun->allocmap_valid) {
+ bitmap_zero(iscsilun->allocmap_valid, iscsilun->allocmap_size);
+ }
+}
+
+static inline bool
+iscsi_allocmap_is_allocated(IscsiLun *iscsilun, int64_t sector_num,
+ int nb_sectors)
+{
+ unsigned long size;
+ if (iscsilun->allocmap == NULL) {
+ return true;
+ }
+ size = DIV_ROUND_UP(sector_num + nb_sectors, iscsilun->cluster_sectors);
+ return !(find_next_bit(iscsilun->allocmap, size,
+ sector_num / iscsilun->cluster_sectors) == size);
+}
+
+static inline bool iscsi_allocmap_is_valid(IscsiLun *iscsilun,
+ int64_t sector_num, int nb_sectors)
+{
+ unsigned long size;
+ if (iscsilun->allocmap_valid == NULL) {
+ return false;
+ }
+ size = DIV_ROUND_UP(sector_num + nb_sectors, iscsilun->cluster_sectors);
+ return (find_next_zero_bit(iscsilun->allocmap_valid, size,
+ sector_num / iscsilun->cluster_sectors) == size);
}
static int coroutine_fn
@@ -517,26 +629,16 @@
}
if (iTask.status != SCSI_STATUS_GOOD) {
+ iscsi_allocmap_set_invalid(iscsilun, sector_num, nb_sectors);
return iTask.err_code;
}
- iscsi_allocationmap_set(iscsilun, sector_num, nb_sectors);
+ iscsi_allocmap_set_allocated(iscsilun, sector_num, nb_sectors);
return 0;
}
-static bool iscsi_allocationmap_is_allocated(IscsiLun *iscsilun,
- int64_t sector_num, int nb_sectors)
-{
- unsigned long size;
- if (iscsilun->allocationmap == NULL) {
- return true;
- }
- size = DIV_ROUND_UP(sector_num + nb_sectors, iscsilun->cluster_sectors);
- return !(find_next_bit(iscsilun->allocationmap, size,
- sector_num / iscsilun->cluster_sectors) == size);
-}
static int64_t coroutine_fn iscsi_co_get_block_status(BlockDriverState *bs,
int64_t sector_num,
@@ -621,9 +723,9 @@
}
if (ret & BDRV_BLOCK_ZERO) {
- iscsi_allocationmap_clear(iscsilun, sector_num, *pnum);
+ iscsi_allocmap_set_unallocated(iscsilun, sector_num, *pnum);
} else {
- iscsi_allocationmap_set(iscsilun, sector_num, *pnum);
+ iscsi_allocmap_set_allocated(iscsilun, sector_num, *pnum);
}
if (*pnum > nb_sectors) {
@@ -659,17 +761,32 @@
return -EINVAL;
}
- if (iscsilun->lbprz && nb_sectors >= ISCSI_CHECKALLOC_THRES &&
- !iscsi_allocationmap_is_allocated(iscsilun, sector_num, nb_sectors)) {
- int64_t ret;
+ /* if cache.direct is off and we have a valid entry in our allocation map
+ * we can skip checking the block status and directly return zeroes if
+ * the request falls within an unallocated area */
+ if (iscsi_allocmap_is_valid(iscsilun, sector_num, nb_sectors) &&
+ !iscsi_allocmap_is_allocated(iscsilun, sector_num, nb_sectors)) {
+ qemu_iovec_memset(iov, 0, 0x00, iov->size);
+ return 0;
+ }
+
+ if (nb_sectors >= ISCSI_CHECKALLOC_THRES &&
+ !iscsi_allocmap_is_valid(iscsilun, sector_num, nb_sectors) &&
+ !iscsi_allocmap_is_allocated(iscsilun, sector_num, nb_sectors)) {
int pnum;
BlockDriverState *file;
- ret = iscsi_co_get_block_status(bs, sector_num,
- BDRV_REQUEST_MAX_SECTORS, &pnum, &file);
+ /* check the block status from the beginning of the cluster
+ * containing the start sector */
+ int64_t ret = iscsi_co_get_block_status(bs,
+ sector_num - sector_num % iscsilun->cluster_sectors,
+ BDRV_REQUEST_MAX_SECTORS, &pnum, &file);
if (ret < 0) {
return ret;
}
- if (ret & BDRV_BLOCK_ZERO && pnum >= nb_sectors) {
+ /* if the whole request falls into an unallocated area we can avoid
+ * to read and directly return zeroes instead */
+ if (ret & BDRV_BLOCK_ZERO &&
+ pnum >= nb_sectors + sector_num % iscsilun->cluster_sectors) {
qemu_iovec_memset(iov, 0, 0x00, iov->size);
return 0;
}
@@ -983,7 +1100,7 @@
return iTask.err_code;
}
- iscsi_allocationmap_clear(iscsilun, sector_num, nb_sectors);
+ iscsi_allocmap_set_invalid(iscsilun, sector_num, nb_sectors);
return 0;
}
@@ -1073,15 +1190,17 @@
}
if (iTask.status != SCSI_STATUS_GOOD) {
+ iscsi_allocmap_set_invalid(iscsilun, offset >> BDRV_SECTOR_BITS,
+ count >> BDRV_SECTOR_BITS);
return iTask.err_code;
}
if (flags & BDRV_REQ_MAY_UNMAP) {
- iscsi_allocationmap_clear(iscsilun, offset >> BDRV_SECTOR_BITS,
- count >> BDRV_SECTOR_BITS);
+ iscsi_allocmap_set_invalid(iscsilun, offset >> BDRV_SECTOR_BITS,
+ count >> BDRV_SECTOR_BITS);
} else {
- iscsi_allocationmap_set(iscsilun, offset >> BDRV_SECTOR_BITS,
- count >> BDRV_SECTOR_BITS);
+ iscsi_allocmap_set_allocated(iscsilun, offset >> BDRV_SECTOR_BITS,
+ count >> BDRV_SECTOR_BITS);
}
return 0;
@@ -1654,10 +1773,7 @@
iscsilun->cluster_sectors = (iscsilun->bl.opt_unmap_gran *
iscsilun->block_size) >> BDRV_SECTOR_BITS;
if (iscsilun->lbprz) {
- iscsilun->allocationmap = iscsi_allocationmap_init(iscsilun);
- if (iscsilun->allocationmap == NULL) {
- ret = -ENOMEM;
- }
+ ret = iscsi_allocmap_init(iscsilun, bs->open_flags);
}
}
@@ -1694,7 +1810,7 @@
}
iscsi_destroy_context(iscsi);
g_free(iscsilun->zeroblock);
- g_free(iscsilun->allocationmap);
+ iscsi_allocmap_free(iscsilun);
memset(iscsilun, 0, sizeof(IscsiLun));
}
@@ -1758,6 +1874,16 @@
return 0;
}
+static void iscsi_reopen_commit(BDRVReopenState *reopen_state)
+{
+ IscsiLun *iscsilun = reopen_state->bs->opaque;
+
+ /* the cache.direct status might have changed */
+ if (iscsilun->allocmap != NULL) {
+ iscsi_allocmap_init(iscsilun, reopen_state->flags);
+ }
+}
+
static int iscsi_truncate(BlockDriverState *bs, int64_t offset)
{
IscsiLun *iscsilun = bs->opaque;
@@ -1777,9 +1903,8 @@
return -EINVAL;
}
- if (iscsilun->allocationmap != NULL) {
- g_free(iscsilun->allocationmap);
- iscsilun->allocationmap = iscsi_allocationmap_init(iscsilun);
+ if (iscsilun->allocmap != NULL) {
+ iscsi_allocmap_init(iscsilun, bs->open_flags);
}
return 0;
@@ -1839,6 +1964,13 @@
return 0;
}
+static void iscsi_invalidate_cache(BlockDriverState *bs,
+ Error **errp)
+{
+ IscsiLun *iscsilun = bs->opaque;
+ iscsi_allocmap_invalidate(iscsilun);
+}
+
static QemuOptsList iscsi_create_opts = {
.name = "iscsi-create-opts",
.head = QTAILQ_HEAD_INITIALIZER(iscsi_create_opts.head),
@@ -1862,7 +1994,9 @@
.bdrv_close = iscsi_close,
.bdrv_create = iscsi_create,
.create_opts = &iscsi_create_opts,
- .bdrv_reopen_prepare = iscsi_reopen_prepare,
+ .bdrv_reopen_prepare = iscsi_reopen_prepare,
+ .bdrv_reopen_commit = iscsi_reopen_commit,
+ .bdrv_invalidate_cache = iscsi_invalidate_cache,
.bdrv_getlength = iscsi_getlength,
.bdrv_get_info = iscsi_get_info,
