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btrfs: have multiple discard lists

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Non-block group destruction discarding currently only had a single list
with no minimum discard length. This can lead to caravaning more
meaningful discards behind a heavily fragmented block group.

This adds support for multiple lists with minimum discard lengths to
prevent the caravan effect. We promote block groups back up when we
exceed the BTRFS_ASYNC_DISCARD_MAX_FILTER size, currently we support
only 2 lists with filters of 1MB and 32KB respectively.

Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Dennis Zhou <dennis@kernel.org>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Dennis Zhou 2020-01-02 16:26:39 -05:00 committed by David Sterba
parent 19b2a2c719
commit 7fe6d45e40
5 changed files with 145 additions and 24 deletions
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2
fs/btrfs/ctree.h
View File

@ -456,7 +456,7 @@ struct btrfs_full_stripe_locks_tree {
* afterwards represent monotonically decreasing discard filter sizes to
* prioritize what should be discarded next.
*/
#define BTRFS_NR_DISCARD_LISTS 2
#define BTRFS_NR_DISCARD_LISTS 3
#define BTRFS_DISCARD_INDEX_UNUSED 0
#define BTRFS_DISCARD_INDEX_START 1

105
fs/btrfs/discard.c
View File

@ -22,6 +22,13 @@
#define BTRFS_DISCARD_MAX_DELAY_MSEC (1000UL)
#define BTRFS_DISCARD_MAX_IOPS (10U)
/* Montonically decreasing minimum length filters after index 0 */
static int discard_minlen[BTRFS_NR_DISCARD_LISTS] = {
0,
BTRFS_ASYNC_DISCARD_MAX_FILTER,
BTRFS_ASYNC_DISCARD_MIN_FILTER
};
static struct list_head *get_discard_list(struct btrfs_discard_ctl *discard_ctl,
struct btrfs_block_group *block_group)
{
@ -139,16 +146,18 @@ static struct btrfs_block_group *find_next_block_group(
* peek_discard_list - wrap find_next_block_group()
* @discard_ctl: discard control
* @discard_state: the discard_state of the block_group after state management
* @discard_index: the discard_index of the block_group after state management
*
* This wraps find_next_block_group() and sets the block_group to be in use.
* discard_state's control flow is managed here. Variables related to
* discard_state are reset here as needed (eg. discard_cursor). @discard_state
* is remembered as it may change while we're discarding, but we want the
* discard to execute in the context determined here.
* discard_state are reset here as needed (eg discard_cursor). @discard_state
* and @discard_index are remembered as it may change while we're discarding,
* but we want the discard to execute in the context determined here.
*/
static struct btrfs_block_group *peek_discard_list(
struct btrfs_discard_ctl *discard_ctl,
enum btrfs_discard_state *discard_state)
enum btrfs_discard_state *discard_state,
int *discard_index)
{
struct btrfs_block_group *block_group;
const u64 now = ktime_get_ns();
@ -169,6 +178,7 @@ static struct btrfs_block_group *peek_discard_list(
}
discard_ctl->block_group = block_group;
*discard_state = block_group->discard_state;
*discard_index = block_group->discard_index;
} else {
block_group = NULL;
}
@ -178,6 +188,64 @@ static struct btrfs_block_group *peek_discard_list(
return block_group;
}
/**
* btrfs_discard_check_filter - updates a block groups filters
* @block_group: block group of interest
* @bytes: recently freed region size after coalescing
*
* Async discard maintains multiple lists with progressively smaller filters
* to prioritize discarding based on size. Should a free space that matches
* a larger filter be returned to the free_space_cache, prioritize that discard
* by moving @block_group to the proper filter.
*/
void btrfs_discard_check_filter(struct btrfs_block_group *block_group,
u64 bytes)
{
struct btrfs_discard_ctl *discard_ctl;
if (!block_group ||
!btrfs_test_opt(block_group->fs_info, DISCARD_ASYNC))
return;
discard_ctl = &block_group->fs_info->discard_ctl;
if (block_group->discard_index > BTRFS_DISCARD_INDEX_START &&
bytes >= discard_minlen[block_group->discard_index - 1]) {
int i;
remove_from_discard_list(discard_ctl, block_group);
for (i = BTRFS_DISCARD_INDEX_START; i < BTRFS_NR_DISCARD_LISTS;
i++) {
if (bytes >= discard_minlen[i]) {
block_group->discard_index = i;
add_to_discard_list(discard_ctl, block_group);
break;
}
}
}
}
/**
* btrfs_update_discard_index - moves a block group along the discard lists
* @discard_ctl: discard control
* @block_group: block_group of interest
*
* Increment @block_group's discard_index. If it falls of the list, let it be.
* Otherwise add it back to the appropriate list.
*/
static void btrfs_update_discard_index(struct btrfs_discard_ctl *discard_ctl,
struct btrfs_block_group *block_group)
{
block_group->discard_index++;
if (block_group->discard_index == BTRFS_NR_DISCARD_LISTS) {
block_group->discard_index = 1;
return;
}
add_to_discard_list(discard_ctl, block_group);
}
/**
* btrfs_discard_cancel_work - remove a block_group from the discard lists
* @discard_ctl: discard control
@ -295,6 +363,8 @@ static void btrfs_finish_discard_pass(struct btrfs_discard_ctl *discard_ctl,
btrfs_mark_bg_unused(block_group);
else
add_to_discard_unused_list(discard_ctl, block_group);
} else {
btrfs_update_discard_index(discard_ctl, block_group);
}
}
@ -311,25 +381,42 @@ static void btrfs_discard_workfn(struct work_struct *work)
struct btrfs_discard_ctl *discard_ctl;
struct btrfs_block_group *block_group;
enum btrfs_discard_state discard_state;
int discard_index = 0;
u64 trimmed = 0;
u64 minlen = 0;
discard_ctl = container_of(work, struct btrfs_discard_ctl, work.work);
block_group = peek_discard_list(discard_ctl, &discard_state);
block_group = peek_discard_list(discard_ctl, &discard_state,
&discard_index);
if (!block_group || !btrfs_run_discard_work(discard_ctl))
return;
/* Perform discarding */
if (discard_state == BTRFS_DISCARD_BITMAPS)
minlen = discard_minlen[discard_index];
if (discard_state == BTRFS_DISCARD_BITMAPS) {
u64 maxlen = 0;
/*
* Use the previous levels minimum discard length as the max
* length filter. In the case something is added to make a
* region go beyond the max filter, the entire bitmap is set
* back to BTRFS_TRIM_STATE_UNTRIMMED.
*/
if (discard_index != BTRFS_DISCARD_INDEX_UNUSED)
maxlen = discard_minlen[discard_index - 1];
btrfs_trim_block_group_bitmaps(block_group, &trimmed,
block_group->discard_cursor,
btrfs_block_group_end(block_group),
0, true);
else
minlen, maxlen, true);
} else {
btrfs_trim_block_group_extents(block_group, &trimmed,
block_group->discard_cursor,
btrfs_block_group_end(block_group),
0, true);
minlen, true);
}
discard_ctl->prev_discard = trimmed;

5
fs/btrfs/discard.h
View File

@ -11,6 +11,11 @@ struct btrfs_block_group;
/* Discard size limits */
#define BTRFS_ASYNC_DISCARD_DEFAULT_MAX_SIZE (SZ_64M)
#define BTRFS_ASYNC_DISCARD_MAX_FILTER (SZ_1M)
#define BTRFS_ASYNC_DISCARD_MIN_FILTER (SZ_32K)
/* List operations */
void btrfs_discard_check_filter(struct btrfs_block_group *block_group, u64 bytes);
/* Work operations */
void btrfs_discard_cancel_work(struct btrfs_discard_ctl *discard_ctl,

55
fs/btrfs/free-space-cache.c
View File

@ -2465,6 +2465,7 @@ int __btrfs_add_free_space(struct btrfs_fs_info *fs_info,
struct btrfs_block_group *block_group = ctl->private;
struct btrfs_free_space *info;
int ret = 0;
u64 filter_bytes = bytes;
info = kmem_cache_zalloc(btrfs_free_space_cachep, GFP_NOFS);
if (!info)
@ -2501,6 +2502,8 @@ int __btrfs_add_free_space(struct btrfs_fs_info *fs_info,
*/
steal_from_bitmap(ctl, info, true);
filter_bytes = max(filter_bytes, info->bytes);
ret = link_free_space(ctl, info);
if (ret)
kmem_cache_free(btrfs_free_space_cachep, info);
@ -2513,8 +2516,10 @@ int __btrfs_add_free_space(struct btrfs_fs_info *fs_info,
ASSERT(ret != -EEXIST);
}
if (trim_state != BTRFS_TRIM_STATE_TRIMMED)
if (trim_state != BTRFS_TRIM_STATE_TRIMMED) {
btrfs_discard_check_filter(block_group, filter_bytes);
btrfs_discard_queue_work(&fs_info->discard_ctl, block_group);
}
return ret;
}
@ -3478,7 +3483,14 @@ static int trim_no_bitmap(struct btrfs_block_group *block_group,
goto next;
}
unlink_free_space(ctl, entry);
if (max_discard_size && bytes > max_discard_size) {
/*
* Let bytes = BTRFS_MAX_DISCARD_SIZE + X.
* If X < BTRFS_ASYNC_DISCARD_MIN_FILTER, we won't trim
* X when we come back around. So trim it now.
*/
if (max_discard_size &&
bytes >= (max_discard_size +
BTRFS_ASYNC_DISCARD_MIN_FILTER)) {
bytes = max_discard_size;
extent_bytes = max_discard_size;
entry->offset += max_discard_size;
@ -3585,7 +3597,7 @@ static void end_trimming_bitmap(struct btrfs_free_space_ctl *ctl,
*/
static int trim_bitmaps(struct btrfs_block_group *block_group,
u64 *total_trimmed, u64 start, u64 end, u64 minlen,
bool async)
u64 maxlen, bool async)
{
struct btrfs_discard_ctl *discard_ctl =
&block_group->fs_info->discard_ctl;
@ -3613,7 +3625,15 @@ static int trim_bitmaps(struct btrfs_block_group *block_group,
}
entry = tree_search_offset(ctl, offset, 1, 0);
if (!entry || (async && start == offset &&
/*
* Bitmaps are marked trimmed lossily now to prevent constant
* discarding of the same bitmap (the reason why we are bound
* by the filters). So, retrim the block group bitmaps when we
* are preparing to punt to the unused_bgs list. This uses
* @minlen to determine if we are in BTRFS_DISCARD_INDEX_UNUSED
* which is the only discard index which sets minlen to 0.
*/
if (!entry || (async && minlen && start == offset &&
btrfs_free_space_trimmed(entry))) {
spin_unlock(&ctl->tree_lock);
mutex_unlock(&ctl->cache_writeout_mutex);
@ -3634,10 +3654,10 @@ static int trim_bitmaps(struct btrfs_block_group *block_group,
ret2 = search_bitmap(ctl, entry, &start, &bytes, false);
if (ret2 || start >= end) {
/*
* This keeps the invariant that all bytes are trimmed
* if BTRFS_TRIM_STATE_TRIMMED is set on a bitmap.
* We lossily consider a bitmap trimmed if we only skip
* over regions <= BTRFS_ASYNC_DISCARD_MIN_FILTER.
*/
if (ret2 && !minlen)
if (ret2 && minlen <= BTRFS_ASYNC_DISCARD_MIN_FILTER)
end_trimming_bitmap(ctl, entry);
else
entry->trim_state = BTRFS_TRIM_STATE_UNTRIMMED;
@ -3658,14 +3678,21 @@ static int trim_bitmaps(struct btrfs_block_group *block_group,
}
bytes = min(bytes, end - start);
if (bytes < minlen) {
entry->trim_state = BTRFS_TRIM_STATE_UNTRIMMED;
if (bytes < minlen || (async && maxlen && bytes > maxlen)) {
spin_unlock(&ctl->tree_lock);
mutex_unlock(&ctl->cache_writeout_mutex);
goto next;
}
if (async && max_discard_size && bytes > max_discard_size)
/*
* Let bytes = BTRFS_MAX_DISCARD_SIZE + X.
* If X < @minlen, we won't trim X when we come back around.
* So trim it now. We differ here from trimming extents as we
* don't keep individual state per bit.
*/
if (async &&
max_discard_size &&
bytes > (max_discard_size + minlen))
bytes = max_discard_size;
bitmap_clear_bits(ctl, entry, start, bytes);
@ -3773,7 +3800,7 @@ int btrfs_trim_block_group(struct btrfs_block_group *block_group,
if (ret)
goto out;
ret = trim_bitmaps(block_group, trimmed, start, end, minlen, false);
ret = trim_bitmaps(block_group, trimmed, start, end, minlen, 0, false);
div64_u64_rem(end, BITS_PER_BITMAP * ctl->unit, &rem);
/* If we ended in the middle of a bitmap, reset the trimming flag */
if (rem)
@ -3807,7 +3834,7 @@ int btrfs_trim_block_group_extents(struct btrfs_block_group *block_group,
int btrfs_trim_block_group_bitmaps(struct btrfs_block_group *block_group,
u64 *trimmed, u64 start, u64 end, u64 minlen,
bool async)
u64 maxlen, bool async)
{
int ret;
@ -3821,7 +3848,9 @@ int btrfs_trim_block_group_bitmaps(struct btrfs_block_group *block_group,
btrfs_get_block_group_trimming(block_group);
spin_unlock(&block_group->lock);
ret = trim_bitmaps(block_group, trimmed, start, end, minlen, async);
ret = trim_bitmaps(block_group, trimmed, start, end, minlen, maxlen,
async);
btrfs_put_block_group_trimming(block_group);
return ret;

2
fs/btrfs/free-space-cache.h
View File

@ -146,7 +146,7 @@ int btrfs_trim_block_group_extents(struct btrfs_block_group *block_group,
bool async);
int btrfs_trim_block_group_bitmaps(struct btrfs_block_group *block_group,
u64 *trimmed, u64 start, u64 end, u64 minlen,
bool async);
u64 maxlen, bool async);
/* Support functions for running our sanity tests */
#ifdef CONFIG_BTRFS_FS_RUN_SANITY_TESTS