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ext4: Add allocation criteria 1.5 (CR1_5) 

CR1_5 aims to optimize allocations which can't be satisfied in CR1. The
fact that we couldn't find a group in CR1 suggests that it would be
difficult to find a continuous extent to compleltely satisfy our
allocations. So before falling to the slower CR2, in CR1.5 we
proactively trim the the preallocations so we can find a group with
(free / fragments) big enough.  This speeds up our allocation at the
cost of slightly reduced preallocation.

The patch also adds a new sysfs tunable:

* /sys/fs/ext4/<partition>/mb_cr1_5_max_trim_order

This controls how much CR1.5 can trim a request before falling to CR2.
For example, for a request of order 7 and max trim order 2, CR1.5 can
trim this upto order 5.

Suggested-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Signed-off-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Link: https://lore.kernel.org/r/150fdf65c8e4cc4dba71e020ce0859bcf636a5ff.1685449706.git.ojaswin@linux.ibm.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
This commit is contained in:
Ojaswin Mujoo 2023-05-30 18:03:49 +05:30 committed by Theodore Ts'o
parent 856d865c17
commit 7e170922f0
5 changed files with 150 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
fs/ext4/ext4.h
View File

@ -133,13 +133,14 @@ enum SHIFT_DIRECTION {
* criteria the slower the allocation. We start at lower criterias and keep
* falling back to higher ones if we are not able to find any blocks.
*/
#define EXT4_MB_NUM_CRS 4
#define EXT4_MB_NUM_CRS 5
/*
* All possible allocation criterias for mballoc
*/
enum criteria {
CR0,
CR1,
CR1_5,
CR2,
CR3,
};
@ -185,6 +186,9 @@ enum criteria {
#define EXT4_MB_CR0_OPTIMIZED 0x8000
/* Avg fragment size rb tree lookup succeeded at least once for cr = 1 */
#define EXT4_MB_CR1_OPTIMIZED 0x00010000
/* Avg fragment size rb tree lookup succeeded at least once for cr = 1.5 */
#define EXT4_MB_CR1_5_OPTIMIZED 0x00020000
struct ext4_allocation_request {
/* target inode for block we're allocating */
struct inode *inode;
@ -1549,6 +1553,7 @@ struct ext4_sb_info {
unsigned long s_mb_last_start;
unsigned int s_mb_prefetch;
unsigned int s_mb_prefetch_limit;
unsigned int s_mb_cr1_5_max_trim_order;
/* stats for buddy allocator */
atomic_t s_bal_reqs; /* number of reqs with len > 1 */
@ -1563,6 +1568,7 @@ struct ext4_sb_info {
atomic_t s_bal_2orders; /* 2^order hits */
atomic_t s_bal_cr0_bad_suggestions;
atomic_t s_bal_cr1_bad_suggestions;
atomic_t s_bal_cr1_5_bad_suggestions;
atomic64_t s_bal_cX_groups_considered[EXT4_MB_NUM_CRS];
atomic64_t s_bal_cX_hits[EXT4_MB_NUM_CRS];
atomic64_t s_bal_cX_failed[EXT4_MB_NUM_CRS]; /* cX loop didn't find blocks */

135
fs/ext4/mballoc.c
View File

@ -165,6 +165,14 @@
* equal to request size using our average fragment size group lists (data
* structure 2) in O(1) time.
*
* At CR1.5 (aka CR1_5), we aim to optimize allocations which can't be satisfied
* in CR1. The fact that we couldn't find a group in CR1 suggests that there is
* no BG that has average fragment size > goal length. So before falling to the
* slower CR2, in CR1.5 we proactively trim goal length and then use the same
* fragment lists as CR1 to find a BG with a big enough average fragment size.
* This increases the chances of finding a suitable block group in O(1) time and
* results * in faster allocation at the cost of reduced size of allocation.
*
* If "mb_optimize_scan" mount option is not set, mballoc traverses groups in
* linear order which requires O(N) search time for each CR0 and CR1 phase.
*
@ -962,6 +970,91 @@ static void ext4_mb_choose_next_group_cr1(struct ext4_allocation_context *ac,
*group = grp->bb_group;
ac->ac_flags |= EXT4_MB_CR1_OPTIMIZED;
} else {
*new_cr = CR1_5;
}
}
/*
* We couldn't find a group in CR1 so try to find the highest free fragment
* order we have and proactively trim the goal request length to that order to
* find a suitable group faster.
*
* This optimizes allocation speed at the cost of slightly reduced
* preallocations. However, we make sure that we don't trim the request too
* much and fall to CR2 in that case.
*/
static void ext4_mb_choose_next_group_cr1_5(struct ext4_allocation_context *ac,
enum criteria *new_cr, ext4_group_t *group, ext4_group_t ngroups)
{
struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
struct ext4_group_info *grp = NULL;
int i, order, min_order;
unsigned long num_stripe_clusters = 0;
if (unlikely(ac->ac_flags & EXT4_MB_CR1_5_OPTIMIZED)) {
if (sbi->s_mb_stats)
atomic_inc(&sbi->s_bal_cr1_5_bad_suggestions);
}
/*
* mb_avg_fragment_size_order() returns order in a way that makes
* retrieving back the length using (1 << order) inaccurate. Hence, use
* fls() instead since we need to know the actual length while modifying
* goal length.
*/
order = fls(ac->ac_g_ex.fe_len);
min_order = order - sbi->s_mb_cr1_5_max_trim_order;
if (min_order < 0)
min_order = 0;
if (1 << min_order < ac->ac_o_ex.fe_len)
min_order = fls(ac->ac_o_ex.fe_len) + 1;
if (sbi->s_stripe > 0) {
/*
* We are assuming that stripe size is always a multiple of
* cluster ratio otherwise __ext4_fill_super exists early.
*/
num_stripe_clusters = EXT4_NUM_B2C(sbi, sbi->s_stripe);
if (1 << min_order < num_stripe_clusters)
min_order = fls(num_stripe_clusters);
}
for (i = order; i >= min_order; i--) {
int frag_order;
/*
* Scale down goal len to make sure we find something
* in the free fragments list. Basically, reduce
* preallocations.
*/
ac->ac_g_ex.fe_len = 1 << i;
if (num_stripe_clusters > 0) {
/*
* Try to round up the adjusted goal to stripe size
* (in cluster units) multiple for efficiency.
*
* XXX: Is s->stripe always a power of 2? In that case
* we can use the faster round_up() variant.
*/
ac->ac_g_ex.fe_len = roundup(ac->ac_g_ex.fe_len,
num_stripe_clusters);
}
frag_order = mb_avg_fragment_size_order(ac->ac_sb,
ac->ac_g_ex.fe_len);
grp = ext4_mb_find_good_group_avg_frag_lists(ac, frag_order);
if (grp)
break;
}
if (grp) {
*group = grp->bb_group;
ac->ac_flags |= EXT4_MB_CR1_5_OPTIMIZED;
} else {
/* Reset goal length to original goal length before falling into CR2 */
ac->ac_g_ex.fe_len = ac->ac_orig_goal_len;
*new_cr = CR2;
}
}
@ -1028,6 +1121,8 @@ static void ext4_mb_choose_next_group(struct ext4_allocation_context *ac,
ext4_mb_choose_next_group_cr0(ac, new_cr, group, ngroups);
} else if (*new_cr == CR1) {
ext4_mb_choose_next_group_cr1(ac, new_cr, group, ngroups);
} else if (*new_cr == CR1_5) {
ext4_mb_choose_next_group_cr1_5(ac, new_cr, group, ngroups);
} else {
/*
* TODO: For CR=2, we can arrange groups in an rb tree sorted by
@ -2351,7 +2446,7 @@ void ext4_mb_complex_scan_group(struct ext4_allocation_context *ac,
if (ac->ac_criteria < CR2) {
/*
* In CR1, we are sure that this group will
* In CR1 and CR1_5, we are sure that this group will
* have a large enough continuous free extent, so skip
* over the smaller free extents
*/
@ -2483,6 +2578,7 @@ static bool ext4_mb_good_group(struct ext4_allocation_context *ac,
return true;
case CR1:
case CR1_5:
if ((free / fragments) >= ac->ac_g_ex.fe_len)
return true;
break;
@ -2747,7 +2843,7 @@ repeat:
* spend a lot of time loading imperfect groups
*/
if ((prefetch_grp == group) &&
(cr > CR1 ||
(cr > CR1_5 ||
prefetch_ios < sbi->s_mb_prefetch_limit)) {
nr = sbi->s_mb_prefetch;
if (ext4_has_feature_flex_bg(sb)) {
@ -2787,7 +2883,7 @@ repeat:
ac->ac_groups_scanned++;
if (cr == CR0)
ext4_mb_simple_scan_group(ac, &e4b);
else if (cr == CR1 && sbi->s_stripe &&
else if ((cr == CR1 || cr == CR1_5) && sbi->s_stripe &&
!(ac->ac_g_ex.fe_len %
EXT4_B2C(sbi, sbi->s_stripe)))
ext4_mb_scan_aligned(ac, &e4b);
@ -2803,6 +2899,11 @@ repeat:
/* Processed all groups and haven't found blocks */
if (sbi->s_mb_stats && i == ngroups)
atomic64_inc(&sbi->s_bal_cX_failed[cr]);
if (i == ngroups && ac->ac_criteria == CR1_5)
/* Reset goal length to original goal length before
* falling into CR2 */
ac->ac_g_ex.fe_len = ac->ac_orig_goal_len;
}
if (ac->ac_b_ex.fe_len > 0 && ac->ac_status != AC_STATUS_FOUND &&
@ -2972,6 +3073,16 @@ int ext4_seq_mb_stats_show(struct seq_file *seq, void *offset)
seq_printf(seq, "\t\tbad_suggestions: %u\n",
atomic_read(&sbi->s_bal_cr1_bad_suggestions));
seq_puts(seq, "\tcr1.5_stats:\n");
seq_printf(seq, "\t\thits: %llu\n", atomic64_read(&sbi->s_bal_cX_hits[CR1_5]));
seq_printf(seq, "\t\tgroups_considered: %llu\n",
atomic64_read(&sbi->s_bal_cX_groups_considered[CR1_5]));
seq_printf(seq, "\t\textents_scanned: %u\n", atomic_read(&sbi->s_bal_cX_ex_scanned[CR1_5]));
seq_printf(seq, "\t\tuseless_loops: %llu\n",
atomic64_read(&sbi->s_bal_cX_failed[CR1_5]));
seq_printf(seq, "\t\tbad_suggestions: %u\n",
atomic_read(&sbi->s_bal_cr1_5_bad_suggestions));
seq_puts(seq, "\tcr2_stats:\n");
seq_printf(seq, "\t\thits: %llu\n", atomic64_read(&sbi->s_bal_cX_hits[CR2]));
seq_printf(seq, "\t\tgroups_considered: %llu\n",
@ -3489,6 +3600,8 @@ int ext4_mb_init(struct super_block *sb)
sbi->s_mb_stats = MB_DEFAULT_STATS;
sbi->s_mb_stream_request = MB_DEFAULT_STREAM_THRESHOLD;
sbi->s_mb_order2_reqs = MB_DEFAULT_ORDER2_REQS;
sbi->s_mb_cr1_5_max_trim_order = MB_DEFAULT_CR1_5_TRIM_ORDER;
/*
* The default group preallocation is 512, which for 4k block
* sizes translates to 2 megabytes. However for bigalloc file
@ -4392,6 +4505,7 @@ ext4_mb_normalize_request(struct ext4_allocation_context *ac,
* placement or satisfy big request as is */
ac->ac_g_ex.fe_logical = start;
ac->ac_g_ex.fe_len = EXT4_NUM_B2C(sbi, size);
ac->ac_orig_goal_len = ac->ac_g_ex.fe_len;
/* define goal start in order to merge */
if (ar->pright && (ar->lright == (start + size)) &&
@ -4435,8 +4549,10 @@ static void ext4_mb_collect_stats(struct ext4_allocation_context *ac)
if (ac->ac_g_ex.fe_start == ac->ac_b_ex.fe_start &&
ac->ac_g_ex.fe_group == ac->ac_b_ex.fe_group)
atomic_inc(&sbi->s_bal_goals);
if (ac->ac_f_ex.fe_len == ac->ac_g_ex.fe_len)
/* did we allocate as much as normalizer originally wanted? */
if (ac->ac_f_ex.fe_len == ac->ac_orig_goal_len)
atomic_inc(&sbi->s_bal_len_goals);
if (ac->ac_found > sbi->s_mb_max_to_scan)
atomic_inc(&sbi->s_bal_breaks);
}
@ -4921,7 +5037,7 @@ ext4_mb_new_inode_pa(struct ext4_allocation_context *ac)
pa = ac->ac_pa;
if (ac->ac_b_ex.fe_len < ac->ac_g_ex.fe_len) {
if (ac->ac_b_ex.fe_len < ac->ac_orig_goal_len) {
int new_bex_start;
int new_bex_end;
@ -4936,14 +5052,14 @@ ext4_mb_new_inode_pa(struct ext4_allocation_context *ac)
* fragmentation in check while ensuring logical range of best
* extent doesn't overflow out of goal extent:
*
* 1. Check if best ex can be kept at end of goal and still
* cover original start
* 1. Check if best ex can be kept at end of goal (before
* cr_best_avail trimmed it) and still cover original start
* 2. Else, check if best ex can be kept at start of goal and
* still cover original start
* 3. Else, keep the best ex at start of original request.
*/
new_bex_end = ac->ac_g_ex.fe_logical +
EXT4_C2B(sbi, ac->ac_g_ex.fe_len);
EXT4_C2B(sbi, ac->ac_orig_goal_len);
new_bex_start = new_bex_end - EXT4_C2B(sbi, ac->ac_b_ex.fe_len);
if (ac->ac_o_ex.fe_logical >= new_bex_start)
goto adjust_bex;
@ -4964,7 +5080,7 @@ adjust_bex:
BUG_ON(ac->ac_o_ex.fe_logical < ac->ac_b_ex.fe_logical);
BUG_ON(ac->ac_o_ex.fe_len > ac->ac_b_ex.fe_len);
BUG_ON(new_bex_end > (ac->ac_g_ex.fe_logical +
EXT4_C2B(sbi, ac->ac_g_ex.fe_len)));
EXT4_C2B(sbi, ac->ac_orig_goal_len)));
}
pa->pa_lstart = ac->ac_b_ex.fe_logical;
@ -5584,6 +5700,7 @@ ext4_mb_initialize_context(struct ext4_allocation_context *ac,
ac->ac_o_ex.fe_start = block;
ac->ac_o_ex.fe_len = len;
ac->ac_g_ex = ac->ac_o_ex;
ac->ac_orig_goal_len = ac->ac_g_ex.fe_len;
ac->ac_flags = ar->flags;
/* we have to define context: we'll work with a file or

13
fs/ext4/mballoc.h
View File

@ -85,6 +85,13 @@
*/
#define MB_DEFAULT_LINEAR_SCAN_THRESHOLD 16
/*
* The maximum order upto which CR1.5 can trim a particular allocation request.
* Example, if we have an order 7 request and max trim order of 3, CR1.5 can
* trim this upto order 4.
*/
#define MB_DEFAULT_CR1_5_TRIM_ORDER 3
/*
* Number of valid buddy orders
*/
@ -179,6 +186,12 @@ struct ext4_allocation_context {
/* copy of the best found extent taken before preallocation efforts */
struct ext4_free_extent ac_f_ex;
/*
* goal len can change in CR1.5, so save the original len. This is
* used while adjusting the PA window and for accounting.
*/
ext4_grpblk_t ac_orig_goal_len;
__u32 ac_groups_considered;
__u32 ac_flags; /* allocation hints */
__u16 ac_groups_scanned;

2
fs/ext4/sysfs.c
View File

@ -223,6 +223,7 @@ EXT4_RW_ATTR_SBI_UI(warning_ratelimit_interval_ms, s_warning_ratelimit_state.int
EXT4_RW_ATTR_SBI_UI(warning_ratelimit_burst, s_warning_ratelimit_state.burst);
EXT4_RW_ATTR_SBI_UI(msg_ratelimit_interval_ms, s_msg_ratelimit_state.interval);
EXT4_RW_ATTR_SBI_UI(msg_ratelimit_burst, s_msg_ratelimit_state.burst);
EXT4_RW_ATTR_SBI_UI(mb_cr1_5_max_trim_order, s_mb_cr1_5_max_trim_order);
#ifdef CONFIG_EXT4_DEBUG
EXT4_RW_ATTR_SBI_UL(simulate_fail, s_simulate_fail);
#endif
@ -273,6 +274,7 @@ static struct attribute *ext4_attrs[] = {
ATTR_LIST(warning_ratelimit_burst),
ATTR_LIST(msg_ratelimit_interval_ms),
ATTR_LIST(msg_ratelimit_burst),
ATTR_LIST(mb_cr1_5_max_trim_order),
ATTR_LIST(errors_count),
ATTR_LIST(warning_count),
ATTR_LIST(msg_count),

2
include/trace/events/ext4.h
View File

@ -122,6 +122,7 @@ TRACE_DEFINE_ENUM(EXT4_FC_REASON_MAX);
TRACE_DEFINE_ENUM(CR0);
TRACE_DEFINE_ENUM(CR1);
TRACE_DEFINE_ENUM(CR1_5);
TRACE_DEFINE_ENUM(CR2);
TRACE_DEFINE_ENUM(CR3);
@ -129,6 +130,7 @@ TRACE_DEFINE_ENUM(CR3);
__print_symbolic(cr, \
{ CR0, "CR0" }, \
{ CR1, "CR1" }, \
{ CR1_5, "CR1.5" } \
{ CR2, "CR2" }, \
{ CR3, "CR3" })