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block/iscsi: allow caching of the allocation map

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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>
This commit is contained in:
Peter Lieven 2016-07-18 10:52:20 +02:00 committed by Paolo Bonzini
parent eb36b953e0
commit e1123a3b40
1 changed files with 192 additions and 58 deletions
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250
block/iscsi.c
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@ -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 @@ typedef struct IscsiLun {
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 @@ static bool is_sector_request_lun_aligned(int64_t sector_num, int nb_sectors,
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 @@ retry:
}
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 @@ retry:
}
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 @@ static int coroutine_fn iscsi_co_readv(BlockDriverState *bs,
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 @@ retry:
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 @@ retry:
}
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 @@ static int iscsi_open(BlockDriverState *bs, QDict *options, int flags,
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 @@ static void iscsi_close(BlockDriverState *bs)
}
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 @@ static int iscsi_reopen_prepare(BDRVReopenState *state,
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 @@ static int iscsi_truncate(BlockDriverState *bs, int64_t offset)
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 @@ static int iscsi_get_info(BlockDriverState *bs, BlockDriverInfo *bdi)
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 @@ static BlockDriver bdrv_iscsi = {
.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,