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Message-Id: <E70919BD-0CA3-4584-A939-3C8A467039EB@dilger.ca>
Date: Tue, 30 Mar 2021 09:29:52 -0700
From: Andreas Dilger <adilger@...ger.ca>
To: harshad shirwadkar <harshadshirwadkar@...il.com>
Cc: Ext4 Developers List <linux-ext4@...r.kernel.org>,
kernel test robot <lkp@...el.com>,
Dan Carpenter <dan.carpenter@...cle.com>,
Alex Zhuravlev <bzzz@...mcloud.com>
Subject: Re: [PATCH v5 5/6] ext4: improve cr 0 / cr 1 group scanning
On Mar 30, 2021, at 09:20, harshad shirwadkar <harshadshirwadkar@...il.com> wrote:
>
> I ran some experiments this morning and here are the results:
>
> 1) Config 1:
> - add change to skip CR0 / CR1 optimizations and fall back to
> linear search when all groups are not loaded
> - prefetch block bitmaps mount option turned off
> - first_write_latency: 6m 56s
> - number_of_groups_loaded_at_the_end_of_first_write: 30726 out of
> 491520 total
>
> 2) Config 2:
> - add change to skip CR0 / CR1 optimizations and fall back to
> linear search when all groups are not loaded
> - prefetch block bitmaps mount option turned on
> - first_write_latency:4m42s
> - number_of_groups_loaded_at_the_end_of_first_write: 490497 out
> of 491520 total
>
> 3) Config 3:
> - don't fallback to linear search
> - prefetch block bitmaps turned off
> - first_write_latency: 0.13s
> - number_of_groups_loaded_at_the_end_of_first_write: 7 out of 491520 total
>
> 4) Config 4:
> - don't fallback to linear search
> - prefetch block bitmaps turned on
> - first_write_latency: 0.15s
> - number_of_groups_loaded_at_the_end_of_first_write: 48384 out of
> 491520 total
>
> Based on the above numbers, I think we should go for config 4, which
> means we should have prefetch_block_bitmaps turned on when
> mb_optimize_scan is on. What do you think about turning
> prefetch_block_bitmaps mount option on by default?
I think that makes sense.
>
> - Harshad
>
>> On Mon, Mar 29, 2021 at 9:10 PM Andreas Dilger <adilger@...ger.ca> wrote:
>>
>>> On Mar 29, 2021, at 17:03, harshad shirwadkar <harshadshirwadkar@...il.com> wrote:
>>>
>>> Another problem that I found in the patch was that when all groups are
>>> not loaded, the optimization concludes that CR0 and CR1 cannot be used
>>> for allocation (since these structures aren't populated). The problem
>>> goes away if we also mount with prefetch_block_bitmaps mount option.
>>> But I think if all the groups are not loaded, we should at least fall
>>> back to linear search at CR1. Maybe skipping CR0 is okay.
>>
>> Alex's patch to skip cr0/1 if no groups are loaded is OK, as long as there is
>> some group prefetch is triggered in the background, IMHO, and is there
>> for later allocations.
>>
>> That avoids lots of scanning at mount time if the filesystem is mostly full,
>> and the first allocation is not critical as long as this triggers group reads.
>>
>> Do you have any idea what the performance impact of this is (eg.
>> latency to first write)? Ideally there would be some group prefetch done
>> right at mount time (itable zero thread?) so that if writes are not
>> done *right* after mount there would not be any noticeable latency.
>>
>> Cheers, Andreas
>>
>>>> On Mon, Mar 29, 2021 at 12:32 PM harshad shirwadkar
>>>> <harshadshirwadkar@...il.com> wrote:
>>>>
>>>> Okay sounds good. I'll do that!
>>>>
>>>>> On Mon, Mar 29, 2021 at 12:14 PM Andreas Dilger <adilger@...ger.ca> wrote:
>>>>>
>>>>> On Mar 24, 2021, at 5:19 PM, Harshad Shirwadkar <harshadshirwadkar@...il.com> wrote:
>>>>>>
>>>>>> Instead of traversing through groups linearly, scan groups in specific
>>>>>> orders at cr 0 and cr 1. At cr 0, we want to find groups that have the
>>>>>> largest free order >= the order of the request. So, with this patch,
>>>>>> we maintain lists for each possible order and insert each group into a
>>>>>> list based on the largest free order in its buddy bitmap. During cr 0
>>>>>> allocation, we traverse these lists in the increasing order of largest
>>>>>> free orders. This allows us to find a group with the best available cr
>>>>>> 0 match in constant time. If nothing can be found, we fallback to cr 1
>>>>>> immediately.
>>>>>>
>>>>>> At CR1, the story is slightly different. We want to traverse in the
>>>>>> order of increasing average fragment size. For CR1, we maintain a rb
>>>>>> tree of groupinfos which is sorted by average fragment size. Instead
>>>>>> of traversing linearly, at CR1, we traverse in the order of increasing
>>>>>> average fragment size, starting at the most optimal group. This brings
>>>>>> down cr 1 search complexity to log(num groups).
>>>>>>
>>>>>> For cr >= 2, we just perform the linear search as before. Also, in
>>>>>> case of lock contention, we intermittently fallback to linear search
>>>>>> even in CR 0 and CR 1 cases. This allows us to proceed during the
>>>>>> allocation path even in case of high contention.
>>>>>
>>>>> If you are refreshing this patch anyway, could you rename "mb_linear_limit"
>>>>> to "mb_linear_groups" or "mb_max_linear_groups" or similar? It otherwise
>>>>> isn't clear what units the "limit" is in (could be MB/GB or something else).
>>>>>
>>>>> Cheers, Andreas
>>>>>
>>>>>> There is an opportunity to do optimization at CR2 too. That's because
>>>>>> at CR2 we only consider groups where bb_free counter (number of free
>>>>>> blocks) is greater than the request extent size. That's left as future
>>>>>> work.
>>>>>>
>>>>>> All the changes introduced in this patch are protected under a new
>>>>>> mount option "mb_optimize_scan".
>>>>>>
>>>>>> With this patchset, following experiment was performed:
>>>>>>
>>>>>> Created a highly fragmented disk of size 65TB. The disk had no
>>>>>> contiguous 2M regions. Following command was run consecutively for 3
>>>>>> times:
>>>>>>
>>>>>> time dd if=/dev/urandom of=file bs=2M count=10
>>>>>>
>>>>>> Here are the results with and without cr 0/1 optimizations introduced
>>>>>> in this patch:
>>>>>>
>>>>>> |---------+------------------------------+---------------------------|
>>>>>> | | Without CR 0/1 Optimizations | With CR 0/1 Optimizations |
>>>>>> |---------+------------------------------+---------------------------|
>>>>>> | 1st run | 5m1.871s | 2m47.642s |
>>>>>> | 2nd run | 2m28.390s | 0m0.611s |
>>>>>> | 3rd run | 2m26.530s | 0m1.255s |
>>>>>> |---------+------------------------------+---------------------------|
>>>>>>
>>>>>> Signed-off-by: Harshad Shirwadkar <harshadshirwadkar@...il.com>
>>>>>> Reported-by: kernel test robot <lkp@...el.com>
>>>>>> Reported-by: Dan Carpenter <dan.carpenter@...cle.com>
>>>>>> Reviewed-by: Andreas Dilger <adilger@...ger.ca>
>>>>>> ---
>>>>>> fs/ext4/ext4.h | 19 ++-
>>>>>> fs/ext4/mballoc.c | 381 ++++++++++++++++++++++++++++++++++++++++++++--
>>>>>> fs/ext4/mballoc.h | 17 ++-
>>>>>> fs/ext4/super.c | 28 +++-
>>>>>> fs/ext4/sysfs.c | 2 +
>>>>>> 5 files changed, 432 insertions(+), 15 deletions(-)
>>>>>>
>>>>>> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
>>>>>> index 85eeeba3bca3..5930c8cb5159 100644
>>>>>> --- a/fs/ext4/ext4.h
>>>>>> +++ b/fs/ext4/ext4.h
>>>>>> @@ -162,7 +162,10 @@ enum SHIFT_DIRECTION {
>>>>>> #define EXT4_MB_USE_RESERVED 0x2000
>>>>>> /* Do strict check for free blocks while retrying block allocation */
>>>>>> #define EXT4_MB_STRICT_CHECK 0x4000
>>>>>> -
>>>>>> +/* Large fragment size list lookup succeeded at least once for cr = 0 */
>>>>>> +#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
>>>>>> struct ext4_allocation_request {
>>>>>> /* target inode for block we're allocating */
>>>>>> struct inode *inode;
>>>>>> @@ -1247,7 +1250,9 @@ struct ext4_inode_info {
>>>>>> #define EXT4_MOUNT2_JOURNAL_FAST_COMMIT 0x00000010 /* Journal fast commit */
>>>>>> #define EXT4_MOUNT2_DAX_NEVER 0x00000020 /* Do not allow Direct Access */
>>>>>> #define EXT4_MOUNT2_DAX_INODE 0x00000040 /* For printing options only */
>>>>>> -
>>>>>> +#define EXT4_MOUNT2_MB_OPTIMIZE_SCAN 0x00000080 /* Optimize group
>>>>>> + * scanning in mballoc
>>>>>> + */
>>>>>>
>>>>>> #define clear_opt(sb, opt) EXT4_SB(sb)->s_mount_opt &= \
>>>>>> ~EXT4_MOUNT_##opt
>>>>>> @@ -1527,9 +1532,14 @@ struct ext4_sb_info {
>>>>>> unsigned int s_mb_free_pending;
>>>>>> struct list_head s_freed_data_list; /* List of blocks to be freed
>>>>>> after commit completed */
>>>>>> + struct rb_root s_mb_avg_fragment_size_root;
>>>>>> + rwlock_t s_mb_rb_lock;
>>>>>> + struct list_head *s_mb_largest_free_orders;
>>>>>> + rwlock_t *s_mb_largest_free_orders_locks;
>>>>>>
>>>>>> /* tunables */
>>>>>> unsigned long s_stripe;
>>>>>> + unsigned int s_mb_linear_limit;
>>>>>> unsigned int s_mb_stream_request;
>>>>>> unsigned int s_mb_max_to_scan;
>>>>>> unsigned int s_mb_min_to_scan;
>>>>>> @@ -1553,6 +1563,8 @@ struct ext4_sb_info {
>>>>>> atomic_t s_bal_goals; /* goal hits */
>>>>>> atomic_t s_bal_breaks; /* too long searches */
>>>>>> atomic_t s_bal_2orders; /* 2^order hits */
>>>>>> + atomic_t s_bal_cr0_bad_suggestions;
>>>>>> + atomic_t s_bal_cr1_bad_suggestions;
>>>>>> atomic64_t s_bal_cX_groups_considered[4];
>>>>>> atomic64_t s_bal_cX_hits[4];
>>>>>> atomic64_t s_bal_cX_failed[4]; /* cX loop didn't find blocks */
>>>>>> @@ -3309,11 +3321,14 @@ struct ext4_group_info {
>>>>>> ext4_grpblk_t bb_free; /* total free blocks */
>>>>>> ext4_grpblk_t bb_fragments; /* nr of freespace fragments */
>>>>>> ext4_grpblk_t bb_largest_free_order;/* order of largest frag in BG */
>>>>>> + ext4_group_t bb_group; /* Group number */
>>>>>> struct list_head bb_prealloc_list;
>>>>>> #ifdef DOUBLE_CHECK
>>>>>> void *bb_bitmap;
>>>>>> #endif
>>>>>> struct rw_semaphore alloc_sem;
>>>>>> + struct rb_node bb_avg_fragment_size_rb;
>>>>>> + struct list_head bb_largest_free_order_node;
>>>>>> ext4_grpblk_t bb_counters[]; /* Nr of free power-of-two-block
>>>>>> * regions, index is order.
>>>>>> * bb_counters[3] = 5 means
>>>>>> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
>>>>>> index 15127d815461..cbf9a89c0ef5 100644
>>>>>> --- a/fs/ext4/mballoc.c
>>>>>> +++ b/fs/ext4/mballoc.c
>>>>>> @@ -127,11 +127,50 @@
>>>>>> * smallest multiple of the stripe value (sbi->s_stripe) which is
>>>>>> * greater than the default mb_group_prealloc.
>>>>>> *
>>>>>> + * If "mb_optimize_scan" mount option is set, we maintain in memory group info
>>>>>> + * structures in two data structures:
>>>>>> + *
>>>>>> + * 1) Array of largest free order lists (sbi->s_mb_largest_free_orders)
>>>>>> + *
>>>>>> + * Locking: sbi->s_mb_largest_free_orders_locks(array of rw locks)
>>>>>> + *
>>>>>> + * This is an array of lists where the index in the array represents the
>>>>>> + * largest free order in the buddy bitmap of the participating group infos of
>>>>>> + * that list. So, there are exactly MB_NUM_ORDERS(sb) (which means total
>>>>>> + * number of buddy bitmap orders possible) number of lists. Group-infos are
>>>>>> + * placed in appropriate lists.
>>>>>> + *
>>>>>> + * 2) Average fragment size rb tree (sbi->s_mb_avg_fragment_size_root)
>>>>>> + *
>>>>>> + * Locking: sbi->s_mb_rb_lock (rwlock)
>>>>>> + *
>>>>>> + * This is a red black tree consisting of group infos and the tree is sorted
>>>>>> + * by average fragment sizes (which is calculated as ext4_group_info->bb_free
>>>>>> + * / ext4_group_info->bb_fragments).
>>>>>> + *
>>>>>> + * When "mb_optimize_scan" mount option is set, mballoc consults the above data
>>>>>> + * structures to decide the order in which groups are to be traversed for
>>>>>> + * fulfilling an allocation request.
>>>>>> + *
>>>>>> + * At CR = 0, we look for groups which have the largest_free_order >= the order
>>>>>> + * of the request. We directly look at the largest free order list in the data
>>>>>> + * structure (1) above where largest_free_order = order of the request. If that
>>>>>> + * list is empty, we look at remaining list in the increasing order of
>>>>>> + * largest_free_order. This allows us to perform CR = 0 lookup in O(1) time.
>>>>>> + *
>>>>>> + * At CR = 1, we only consider groups where average fragment size > request
>>>>>> + * size. So, we lookup a group which has average fragment size just above or
>>>>>> + * equal to request size using our rb tree (data structure 2) in O(log N) time.
>>>>>> + *
>>>>>> + * If "mb_optimize_scan" mount option is not set, mballoc traverses groups in
>>>>>> + * linear order which requires O(N) search time for each CR 0 and CR 1 phase.
>>>>>> + *
>>>>>> * The regular allocator (using the buddy cache) supports a few tunables.
>>>>>> *
>>>>>> * /sys/fs/ext4/<partition>/mb_min_to_scan
>>>>>> * /sys/fs/ext4/<partition>/mb_max_to_scan
>>>>>> * /sys/fs/ext4/<partition>/mb_order2_req
>>>>>> + * /sys/fs/ext4/<partition>/mb_linear_limit
>>>>>> *
>>>>>> * The regular allocator uses buddy scan only if the request len is power of
>>>>>> * 2 blocks and the order of allocation is >= sbi->s_mb_order2_reqs. The
>>>>>> @@ -149,6 +188,16 @@
>>>>>> * can be used for allocation. ext4_mb_good_group explains how the groups are
>>>>>> * checked.
>>>>>> *
>>>>>> + * When "mb_optimize_scan" is turned on, as mentioned above, the groups may not
>>>>>> + * get traversed linearly. That may result in subsequent allocations being not
>>>>>> + * close to each other. And so, the underlying device may get filled up in a
>>>>>> + * non-linear fashion. While that may not matter on non-rotational devices, for
>>>>>> + * rotational devices that may result in higher seek times. "mb_linear_limit"
>>>>>> + * tells mballoc how many groups mballoc should search linearly before
>>>>>> + * performing consulting above data structures for more efficient lookups. For
>>>>>> + * non rotational devices, this value defaults to 0 and for rotational devices
>>>>>> + * this is set to MB_DEFAULT_LINEAR_LIMIT.
>>>>>> + *
>>>>>> * Both the prealloc space are getting populated as above. So for the first
>>>>>> * request we will hit the buddy cache which will result in this prealloc
>>>>>> * space getting filled. The prealloc space is then later used for the
>>>>>> @@ -299,6 +348,8 @@
>>>>>> * - bitlock on a group (group)
>>>>>> * - object (inode/locality) (object)
>>>>>> * - per-pa lock (pa)
>>>>>> + * - cr0 lists lock (cr0)
>>>>>> + * - cr1 tree lock (cr1)
>>>>>> *
>>>>>> * Paths:
>>>>>> * - new pa
>>>>>> @@ -328,6 +379,9 @@
>>>>>> * group
>>>>>> * object
>>>>>> *
>>>>>> + * - allocation path (ext4_mb_regular_allocator)
>>>>>> + * group
>>>>>> + * cr0/cr1
>>>>>> */
>>>>>> static struct kmem_cache *ext4_pspace_cachep;
>>>>>> static struct kmem_cache *ext4_ac_cachep;
>>>>>> @@ -351,6 +405,9 @@ static void ext4_mb_generate_from_freelist(struct super_block *sb, void *bitmap,
>>>>>> ext4_group_t group);
>>>>>> static void ext4_mb_new_preallocation(struct ext4_allocation_context *ac);
>>>>>>
>>>>>> +static bool ext4_mb_good_group(struct ext4_allocation_context *ac,
>>>>>> + ext4_group_t group, int cr);
>>>>>> +
>>>>>> /*
>>>>>> * The algorithm using this percpu seq counter goes below:
>>>>>> * 1. We sample the percpu discard_pa_seq counter before trying for block
>>>>>> @@ -744,6 +801,251 @@ static void ext4_mb_mark_free_simple(struct super_block *sb,
>>>>>> }
>>>>>> }
>>>>>>
>>>>>> +static void ext4_mb_rb_insert(struct rb_root *root, struct rb_node *new,
>>>>>> + int (*cmp)(struct rb_node *, struct rb_node *))
>>>>>> +{
>>>>>> + struct rb_node **iter = &root->rb_node, *parent = NULL;
>>>>>> +
>>>>>> + while (*iter) {
>>>>>> + parent = *iter;
>>>>>> + if (cmp(new, *iter) > 0)
>>>>>> + iter = &((*iter)->rb_left);
>>>>>> + else
>>>>>> + iter = &((*iter)->rb_right);
>>>>>> + }
>>>>>> +
>>>>>> + rb_link_node(new, parent, iter);
>>>>>> + rb_insert_color(new, root);
>>>>>> +}
>>>>>> +
>>>>>> +static int
>>>>>> +ext4_mb_avg_fragment_size_cmp(struct rb_node *rb1, struct rb_node *rb2)
>>>>>> +{
>>>>>> + struct ext4_group_info *grp1 = rb_entry(rb1,
>>>>>> + struct ext4_group_info,
>>>>>> + bb_avg_fragment_size_rb);
>>>>>> + struct ext4_group_info *grp2 = rb_entry(rb2,
>>>>>> + struct ext4_group_info,
>>>>>> + bb_avg_fragment_size_rb);
>>>>>> + int num_frags_1, num_frags_2;
>>>>>> +
>>>>>> + num_frags_1 = grp1->bb_fragments ?
>>>>>> + grp1->bb_free / grp1->bb_fragments : 0;
>>>>>> + num_frags_2 = grp2->bb_fragments ?
>>>>>> + grp2->bb_free / grp2->bb_fragments : 0;
>>>>>> +
>>>>>> + return (num_frags_2 - num_frags_1);
>>>>>> +}
>>>>>> +
>>>>>> +/*
>>>>>> + * Reinsert grpinfo into the avg_fragment_size tree with new average
>>>>>> + * fragment size.
>>>>>> + */
>>>>>> +static void
>>>>>> +mb_update_avg_fragment_size(struct super_block *sb, struct ext4_group_info *grp)
>>>>>> +{
>>>>>> + struct ext4_sb_info *sbi = EXT4_SB(sb);
>>>>>> +
>>>>>> + if (!test_opt2(sb, MB_OPTIMIZE_SCAN) || grp->bb_free == 0)
>>>>>> + return;
>>>>>> +
>>>>>> + write_lock(&sbi->s_mb_rb_lock);
>>>>>> + if (!RB_EMPTY_NODE(&grp->bb_avg_fragment_size_rb)) {
>>>>>> + rb_erase(&grp->bb_avg_fragment_size_rb,
>>>>>> + &sbi->s_mb_avg_fragment_size_root);
>>>>>> + RB_CLEAR_NODE(&grp->bb_avg_fragment_size_rb);
>>>>>> + }
>>>>>> +
>>>>>> + ext4_mb_rb_insert(&sbi->s_mb_avg_fragment_size_root,
>>>>>> + &grp->bb_avg_fragment_size_rb,
>>>>>> + ext4_mb_avg_fragment_size_cmp);
>>>>>> + write_unlock(&sbi->s_mb_rb_lock);
>>>>>> +}
>>>>>> +
>>>>>> +/*
>>>>>> + * Choose next group by traversing largest_free_order lists. Return 0 if next
>>>>>> + * group was selected optimally. Return 1 if next group was not selected
>>>>>> + * optimally. Updates *new_cr if cr level needs an update.
>>>>>> + */
>>>>>> +static int ext4_mb_choose_next_group_cr0(struct ext4_allocation_context *ac,
>>>>>> + int *new_cr, ext4_group_t *group, ext4_group_t ngroups)
>>>>>> +{
>>>>>> + struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
>>>>>> + struct ext4_group_info *iter, *grp;
>>>>>> + int i;
>>>>>> +
>>>>>> + if (ac->ac_status == AC_STATUS_FOUND)
>>>>>> + return 1;
>>>>>> +
>>>>>> + if (unlikely(sbi->s_mb_stats && ac->ac_flags & EXT4_MB_CR0_OPTIMIZED))
>>>>>> + atomic_inc(&sbi->s_bal_cr0_bad_suggestions);
>>>>>> +
>>>>>> + grp = NULL;
>>>>>> + for (i = ac->ac_2order; i < MB_NUM_ORDERS(ac->ac_sb); i++) {
>>>>>> + if (list_empty(&sbi->s_mb_largest_free_orders[i]))
>>>>>> + continue;
>>>>>> + read_lock(&sbi->s_mb_largest_free_orders_locks[i]);
>>>>>> + if (list_empty(&sbi->s_mb_largest_free_orders[i])) {
>>>>>> + read_unlock(&sbi->s_mb_largest_free_orders_locks[i]);
>>>>>> + continue;
>>>>>> + }
>>>>>> + grp = NULL;
>>>>>> + list_for_each_entry(iter, &sbi->s_mb_largest_free_orders[i],
>>>>>> + bb_largest_free_order_node) {
>>>>>> + if (sbi->s_mb_stats)
>>>>>> + atomic64_inc(&sbi->s_bal_cX_groups_considered[0]);
>>>>>> + if (likely(ext4_mb_good_group(ac, iter->bb_group, 0))) {
>>>>>> + grp = iter;
>>>>>> + break;
>>>>>> + }
>>>>>> + }
>>>>>> + read_unlock(&sbi->s_mb_largest_free_orders_locks[i]);
>>>>>> + if (grp)
>>>>>> + break;
>>>>>> + }
>>>>>> +
>>>>>> + if (!grp) {
>>>>>> + /* Increment cr and search again */
>>>>>> + *new_cr = 1;
>>>>>> + } else {
>>>>>> + *group = grp->bb_group;
>>>>>> + ac->ac_last_optimal_group = *group;
>>>>>> + ac->ac_flags |= EXT4_MB_CR0_OPTIMIZED;
>>>>>> + }
>>>>>> + return 0;
>>>>>> +}
>>>>>> +
>>>>>> +/*
>>>>>> + * Choose next group by traversing average fragment size tree. Return 0 if next
>>>>>> + * group was selected optimally. Return 1 if next group could not selected
>>>>>> + * optimally (due to lock contention). Updates *new_cr if cr lvel needs an
>>>>>> + * update.
>>>>>> + */
>>>>>> +static int ext4_mb_choose_next_group_cr1(struct ext4_allocation_context *ac,
>>>>>> + int *new_cr, ext4_group_t *group, ext4_group_t ngroups)
>>>>>> +{
>>>>>> + struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
>>>>>> + int avg_fragment_size, best_so_far;
>>>>>> + struct rb_node *node, *found;
>>>>>> + struct ext4_group_info *grp;
>>>>>> +
>>>>>> + /*
>>>>>> + * If there is contention on the lock, instead of waiting for the lock
>>>>>> + * to become available, just continue searching lineraly. We'll resume
>>>>>> + * our rb tree search later starting at ac->ac_last_optimal_group.
>>>>>> + */
>>>>>> + if (!read_trylock(&sbi->s_mb_rb_lock))
>>>>>> + return 1;
>>>>>> +
>>>>>> + if (unlikely(ac->ac_flags & EXT4_MB_CR1_OPTIMIZED)) {
>>>>>> + if (sbi->s_mb_stats)
>>>>>> + atomic_inc(&sbi->s_bal_cr1_bad_suggestions);
>>>>>> + /* We have found something at CR 1 in the past */
>>>>>> + grp = ext4_get_group_info(ac->ac_sb, ac->ac_last_optimal_group);
>>>>>> + for (found = rb_next(&grp->bb_avg_fragment_size_rb); found != NULL;
>>>>>> + found = rb_next(found)) {
>>>>>> + grp = rb_entry(found, struct ext4_group_info,
>>>>>> + bb_avg_fragment_size_rb);
>>>>>> + if (sbi->s_mb_stats)
>>>>>> + atomic64_inc(&sbi->s_bal_cX_groups_considered[1]);
>>>>>> + if (likely(ext4_mb_good_group(ac, grp->bb_group, 1)))
>>>>>> + break;
>>>>>> + }
>>>>>> +
>>>>>> + goto done;
>>>>>> + }
>>>>>> +
>>>>>> + node = sbi->s_mb_avg_fragment_size_root.rb_node;
>>>>>> + best_so_far = 0;
>>>>>> + found = NULL;
>>>>>> +
>>>>>> + while (node) {
>>>>>> + grp = rb_entry(node, struct ext4_group_info,
>>>>>> + bb_avg_fragment_size_rb);
>>>>>> + avg_fragment_size = 0;
>>>>>> + /*
>>>>>> + * Perform this check without locking, we'll lock later to confirm.
>>>>>> + */
>>>>>> + if (ext4_mb_good_group(ac, grp->bb_group, 1)) {
>>>>>> + avg_fragment_size = grp->bb_fragments ?
>>>>>> + grp->bb_free / grp->bb_fragments : 0;
>>>>>> + if (!best_so_far || avg_fragment_size < best_so_far) {
>>>>>> + best_so_far = avg_fragment_size;
>>>>>> + found = node;
>>>>>> + }
>>>>>> + }
>>>>>> + if (avg_fragment_size > ac->ac_g_ex.fe_len)
>>>>>> + node = node->rb_right;
>>>>>> + else
>>>>>> + node = node->rb_left;
>>>>>> + }
>>>>>> +
>>>>>> +done:
>>>>>> + if (found) {
>>>>>> + grp = rb_entry(found, struct ext4_group_info,
>>>>>> + bb_avg_fragment_size_rb);
>>>>>> + *group = grp->bb_group;
>>>>>> + ac->ac_flags |= EXT4_MB_CR1_OPTIMIZED;
>>>>>> + } else {
>>>>>> + *new_cr = 2;
>>>>>> + }
>>>>>> +
>>>>>> + read_unlock(&sbi->s_mb_rb_lock);
>>>>>> + ac->ac_last_optimal_group = *group;
>>>>>> + return 0;
>>>>>> +}
>>>>>> +
>>>>>> +/*
>>>>>> + * ext4_mb_choose_next_group: choose next group for allocation.
>>>>>> + *
>>>>>> + * @ac Allocation Context
>>>>>> + * @new_cr This is an output parameter. If the there is no good group
>>>>>> + * available at current CR level, this field is updated to indicate
>>>>>> + * the new cr level that should be used.
>>>>>> + * @group This is an input / output parameter. As an input it indicates the
>>>>>> + * last group used for allocation. As output, this field indicates
>>>>>> + * the next group that should be used.
>>>>>> + * @ngroups Total number of groups
>>>>>> + */
>>>>>> +static void ext4_mb_choose_next_group(struct ext4_allocation_context *ac,
>>>>>> + int *new_cr, ext4_group_t *group, ext4_group_t ngroups)
>>>>>> +{
>>>>>> + int ret;
>>>>>> +
>>>>>> + *new_cr = ac->ac_criteria;
>>>>>> +
>>>>>> + if (!test_opt2(ac->ac_sb, MB_OPTIMIZE_SCAN) ||
>>>>>> + *new_cr >= 2 ||
>>>>>> + !ext4_test_inode_flag(ac->ac_inode, EXT4_INODE_EXTENTS))
>>>>>> + goto inc_and_return;
>>>>>> +
>>>>>> + if (ac->ac_groups_linear_remaining) {
>>>>>> + ac->ac_groups_linear_remaining--;
>>>>>> + goto inc_and_return;
>>>>>> + }
>>>>>> +
>>>>>> + if (*new_cr == 0) {
>>>>>> + ret = ext4_mb_choose_next_group_cr0(ac, new_cr, group, ngroups);
>>>>>> + if (ret)
>>>>>> + goto inc_and_return;
>>>>>> + }
>>>>>> + if (*new_cr == 1) {
>>>>>> + ret = ext4_mb_choose_next_group_cr1(ac, new_cr, group, ngroups);
>>>>>> + if (ret)
>>>>>> + goto inc_and_return;
>>>>>> + }
>>>>>> + return;
>>>>>> +
>>>>>> +inc_and_return:
>>>>>> + /*
>>>>>> + * Artificially restricted ngroups for non-extent
>>>>>> + * files makes group > ngroups possible on first loop.
>>>>>> + */
>>>>>> + *group = *group + 1;
>>>>>> + if (*group >= ngroups)
>>>>>> + *group = 0;
>>>>>> +}
>>>>>> +
>>>>>> /*
>>>>>> * Cache the order of the largest free extent we have available in this block
>>>>>> * group.
>>>>>> @@ -751,18 +1053,33 @@ static void ext4_mb_mark_free_simple(struct super_block *sb,
>>>>>> static void
>>>>>> mb_set_largest_free_order(struct super_block *sb, struct ext4_group_info *grp)
>>>>>> {
>>>>>> + struct ext4_sb_info *sbi = EXT4_SB(sb);
>>>>>> int i;
>>>>>> - int bits;
>>>>>>
>>>>>> + if (test_opt2(sb, MB_OPTIMIZE_SCAN) && grp->bb_largest_free_order >= 0) {
>>>>>> + write_lock(&sbi->s_mb_largest_free_orders_locks[
>>>>>> + grp->bb_largest_free_order]);
>>>>>> + list_del_init(&grp->bb_largest_free_order_node);
>>>>>> + write_unlock(&sbi->s_mb_largest_free_orders_locks[
>>>>>> + grp->bb_largest_free_order]);
>>>>>> + }
>>>>>> grp->bb_largest_free_order = -1; /* uninit */
>>>>>>
>>>>>> - bits = MB_NUM_ORDERS(sb) - 1;
>>>>>> - for (i = bits; i >= 0; i--) {
>>>>>> + for (i = MB_NUM_ORDERS(sb) - 1; i >= 0; i--) {
>>>>>> if (grp->bb_counters[i] > 0) {
>>>>>> grp->bb_largest_free_order = i;
>>>>>> break;
>>>>>> }
>>>>>> }
>>>>>> + if (test_opt2(sb, MB_OPTIMIZE_SCAN) &&
>>>>>> + grp->bb_largest_free_order >= 0 && grp->bb_free) {
>>>>>> + write_lock(&sbi->s_mb_largest_free_orders_locks[
>>>>>> + grp->bb_largest_free_order]);
>>>>>> + list_add_tail(&grp->bb_largest_free_order_node,
>>>>>> + &sbi->s_mb_largest_free_orders[grp->bb_largest_free_order]);
>>>>>> + write_unlock(&sbi->s_mb_largest_free_orders_locks[
>>>>>> + grp->bb_largest_free_order]);
>>>>>> + }
>>>>>> }
>>>>>>
>>>>>> static noinline_for_stack
>>>>>> @@ -818,6 +1135,7 @@ void ext4_mb_generate_buddy(struct super_block *sb,
>>>>>> period = get_cycles() - period;
>>>>>> atomic_inc(&sbi->s_mb_buddies_generated);
>>>>>> atomic64_add(period, &sbi->s_mb_generation_time);
>>>>>> + mb_update_avg_fragment_size(sb, grp);
>>>>>> }
>>>>>>
>>>>>> /* The buddy information is attached the buddy cache inode
>>>>>> @@ -1517,6 +1835,7 @@ static void mb_free_blocks(struct inode *inode, struct ext4_buddy *e4b,
>>>>>>
>>>>>> done:
>>>>>> mb_set_largest_free_order(sb, e4b->bd_info);
>>>>>> + mb_update_avg_fragment_size(sb, e4b->bd_info);
>>>>>> mb_check_buddy(e4b);
>>>>>> }
>>>>>>
>>>>>> @@ -1653,6 +1972,7 @@ static int mb_mark_used(struct ext4_buddy *e4b, struct ext4_free_extent *ex)
>>>>>> }
>>>>>> mb_set_largest_free_order(e4b->bd_sb, e4b->bd_info);
>>>>>>
>>>>>> + mb_update_avg_fragment_size(e4b->bd_sb, e4b->bd_info);
>>>>>> ext4_set_bits(e4b->bd_bitmap, ex->fe_start, len0);
>>>>>> mb_check_buddy(e4b);
>>>>>>
>>>>>> @@ -2347,17 +2667,21 @@ ext4_mb_regular_allocator(struct ext4_allocation_context *ac)
>>>>>> * from the goal value specified
>>>>>> */
>>>>>> group = ac->ac_g_ex.fe_group;
>>>>>> + ac->ac_last_optimal_group = group;
>>>>>> + ac->ac_groups_linear_remaining = sbi->s_mb_linear_limit;
>>>>>> prefetch_grp = group;
>>>>>>
>>>>>> - for (i = 0; i < ngroups; group++, i++) {
>>>>>> - int ret = 0;
>>>>>> + for (i = 0; i < ngroups; i++) {
>>>>>> + int ret = 0, new_cr;
>>>>>> +
>>>>>> cond_resched();
>>>>>> - /*
>>>>>> - * Artificially restricted ngroups for non-extent
>>>>>> - * files makes group > ngroups possible on first loop.
>>>>>> - */
>>>>>> - if (group >= ngroups)
>>>>>> - group = 0;
>>>>>> +
>>>>>> + ext4_mb_choose_next_group(ac, &new_cr, &group, ngroups);
>>>>>> +
>>>>>> + if (new_cr != cr) {
>>>>>> + cr = new_cr;
>>>>>> + goto repeat;
>>>>>> + }
>>>>>>
>>>>>> /*
>>>>>> * Batch reads of the block allocation bitmaps
>>>>>> @@ -2578,6 +2902,8 @@ int ext4_seq_mb_stats_show(struct seq_file *seq, void *offset)
>>>>>> atomic64_read(&sbi->s_bal_cX_groups_considered[0]));
>>>>>> seq_printf(seq, "\t\tuseless_loops: %llu\n",
>>>>>> atomic64_read(&sbi->s_bal_cX_failed[0]));
>>>>>> + seq_printf(seq, "\t\tbad_suggestions: %u\n",
>>>>>> + atomic_read(&sbi->s_bal_cr0_bad_suggestions));
>>>>>>
>>>>>> seq_puts(seq, "\tcr1_stats:\n");
>>>>>> seq_printf(seq, "\t\thits: %llu\n", atomic64_read(&sbi->s_bal_cX_hits[1]));
>>>>>> @@ -2585,6 +2911,8 @@ int ext4_seq_mb_stats_show(struct seq_file *seq, void *offset)
>>>>>> atomic64_read(&sbi->s_bal_cX_groups_considered[1]));
>>>>>> seq_printf(seq, "\t\tuseless_loops: %llu\n",
>>>>>> atomic64_read(&sbi->s_bal_cX_failed[1]));
>>>>>> + seq_printf(seq, "\t\tbad_suggestions: %u\n",
>>>>>> + atomic_read(&sbi->s_bal_cr1_bad_suggestions));
>>>>>>
>>>>>> seq_puts(seq, "\tcr2_stats:\n");
>>>>>> seq_printf(seq, "\t\thits: %llu\n", atomic64_read(&sbi->s_bal_cX_hits[2]));
>>>>>> @@ -2719,7 +3047,10 @@ int ext4_mb_add_groupinfo(struct super_block *sb, ext4_group_t group,
>>>>>> INIT_LIST_HEAD(&meta_group_info[i]->bb_prealloc_list);
>>>>>> init_rwsem(&meta_group_info[i]->alloc_sem);
>>>>>> meta_group_info[i]->bb_free_root = RB_ROOT;
>>>>>> + INIT_LIST_HEAD(&meta_group_info[i]->bb_largest_free_order_node);
>>>>>> + RB_CLEAR_NODE(&meta_group_info[i]->bb_avg_fragment_size_rb);
>>>>>> meta_group_info[i]->bb_largest_free_order = -1; /* uninit */
>>>>>> + meta_group_info[i]->bb_group = group;
>>>>>>
>>>>>> mb_group_bb_bitmap_alloc(sb, meta_group_info[i], group);
>>>>>> return 0;
>>>>>> @@ -2909,6 +3240,26 @@ int ext4_mb_init(struct super_block *sb)
>>>>>> i++;
>>>>>> } while (i < MB_NUM_ORDERS(sb));
>>>>>>
>>>>>> + sbi->s_mb_avg_fragment_size_root = RB_ROOT;
>>>>>> + sbi->s_mb_largest_free_orders =
>>>>>> + kmalloc_array(MB_NUM_ORDERS(sb), sizeof(struct list_head),
>>>>>> + GFP_KERNEL);
>>>>>> + if (!sbi->s_mb_largest_free_orders) {
>>>>>> + ret = -ENOMEM;
>>>>>> + goto out;
>>>>>> + }
>>>>>> + sbi->s_mb_largest_free_orders_locks =
>>>>>> + kmalloc_array(MB_NUM_ORDERS(sb), sizeof(rwlock_t),
>>>>>> + GFP_KERNEL);
>>>>>> + if (!sbi->s_mb_largest_free_orders_locks) {
>>>>>> + ret = -ENOMEM;
>>>>>> + goto out;
>>>>>> + }
>>>>>> + for (i = 0; i < MB_NUM_ORDERS(sb); i++) {
>>>>>> + INIT_LIST_HEAD(&sbi->s_mb_largest_free_orders[i]);
>>>>>> + rwlock_init(&sbi->s_mb_largest_free_orders_locks[i]);
>>>>>> + }
>>>>>> + rwlock_init(&sbi->s_mb_rb_lock);
>>>>>>
>>>>>> spin_lock_init(&sbi->s_md_lock);
>>>>>> sbi->s_mb_free_pending = 0;
>>>>>> @@ -2961,6 +3312,10 @@ int ext4_mb_init(struct super_block *sb)
>>>>>> spin_lock_init(&lg->lg_prealloc_lock);
>>>>>> }
>>>>>>
>>>>>> + if (blk_queue_nonrot(bdev_get_queue(sb->s_bdev)))
>>>>>> + sbi->s_mb_linear_limit = 0;
>>>>>> + else
>>>>>> + sbi->s_mb_linear_limit = MB_DEFAULT_LINEAR_LIMIT;
>>>>>> /* init file for buddy data */
>>>>>> ret = ext4_mb_init_backend(sb);
>>>>>> if (ret != 0)
>>>>>> @@ -2972,6 +3327,8 @@ int ext4_mb_init(struct super_block *sb)
>>>>>> free_percpu(sbi->s_locality_groups);
>>>>>> sbi->s_locality_groups = NULL;
>>>>>> out:
>>>>>> + kfree(sbi->s_mb_largest_free_orders);
>>>>>> + kfree(sbi->s_mb_largest_free_orders_locks);
>>>>>> kfree(sbi->s_mb_offsets);
>>>>>> sbi->s_mb_offsets = NULL;
>>>>>> kfree(sbi->s_mb_maxs);
>>>>>> @@ -3028,6 +3385,8 @@ int ext4_mb_release(struct super_block *sb)
>>>>>> kvfree(group_info);
>>>>>> rcu_read_unlock();
>>>>>> }
>>>>>> + kfree(sbi->s_mb_largest_free_orders);
>>>>>> + kfree(sbi->s_mb_largest_free_orders_locks);
>>>>>> kfree(sbi->s_mb_offsets);
>>>>>> kfree(sbi->s_mb_maxs);
>>>>>> iput(sbi->s_buddy_cache);
>>>>>> diff --git a/fs/ext4/mballoc.h b/fs/ext4/mballoc.h
>>>>>> index 68111a10cfee..02585e3cbcad 100644
>>>>>> --- a/fs/ext4/mballoc.h
>>>>>> +++ b/fs/ext4/mballoc.h
>>>>>> @@ -78,6 +78,18 @@
>>>>>> */
>>>>>> #define MB_DEFAULT_MAX_INODE_PREALLOC 512
>>>>>>
>>>>>> +/*
>>>>>> + * Number of groups to search linearly before performing group scanning
>>>>>> + * optimization.
>>>>>> + */
>>>>>> +#define MB_DEFAULT_LINEAR_LIMIT 4
>>>>>> +
>>>>>> +/*
>>>>>> + * Minimum number of groups that should be present in the file system to perform
>>>>>> + * group scanning optimizations.
>>>>>> + */
>>>>>> +#define MB_DEFAULT_LINEAR_SCAN_THRESHOLD 16
>>>>>> +
>>>>>> /*
>>>>>> * Number of valid buddy orders
>>>>>> */
>>>>>> @@ -166,11 +178,14 @@ struct ext4_allocation_context {
>>>>>> /* copy of the best found extent taken before preallocation efforts */
>>>>>> struct ext4_free_extent ac_f_ex;
>>>>>>
>>>>>> + ext4_group_t ac_last_optimal_group;
>>>>>> + __u32 ac_groups_considered;
>>>>>> + __u32 ac_flags; /* allocation hints */
>>>>>> __u16 ac_groups_scanned;
>>>>>> + __u16 ac_groups_linear_remaining;
>>>>>> __u16 ac_found;
>>>>>> __u16 ac_tail;
>>>>>> __u16 ac_buddy;
>>>>>> - __u16 ac_flags; /* allocation hints */
>>>>>> __u8 ac_status;
>>>>>> __u8 ac_criteria;
>>>>>> __u8 ac_2order; /* if request is to allocate 2^N blocks and
>>>>>> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
>>>>>> index 3a2cd9fb7e73..6116640081c0 100644
>>>>>> --- a/fs/ext4/super.c
>>>>>> +++ b/fs/ext4/super.c
>>>>>> @@ -1687,7 +1687,7 @@ enum {
>>>>>> Opt_dioread_nolock, Opt_dioread_lock,
>>>>>> Opt_discard, Opt_nodiscard, Opt_init_itable, Opt_noinit_itable,
>>>>>> Opt_max_dir_size_kb, Opt_nojournal_checksum, Opt_nombcache,
>>>>>> - Opt_prefetch_block_bitmaps,
>>>>>> + Opt_prefetch_block_bitmaps, Opt_mb_optimize_scan,
>>>>>> #ifdef CONFIG_EXT4_DEBUG
>>>>>> Opt_fc_debug_max_replay, Opt_fc_debug_force
>>>>>> #endif
>>>>>> @@ -1788,6 +1788,7 @@ static const match_table_t tokens = {
>>>>>> {Opt_nombcache, "nombcache"},
>>>>>> {Opt_nombcache, "no_mbcache"}, /* for backward compatibility */
>>>>>> {Opt_prefetch_block_bitmaps, "prefetch_block_bitmaps"},
>>>>>> + {Opt_mb_optimize_scan, "mb_optimize_scan=%d"},
>>>>>> {Opt_removed, "check=none"}, /* mount option from ext2/3 */
>>>>>> {Opt_removed, "nocheck"}, /* mount option from ext2/3 */
>>>>>> {Opt_removed, "reservation"}, /* mount option from ext2/3 */
>>>>>> @@ -1820,6 +1821,8 @@ static ext4_fsblk_t get_sb_block(void **data)
>>>>>> }
>>>>>>
>>>>>> #define DEFAULT_JOURNAL_IOPRIO (IOPRIO_PRIO_VALUE(IOPRIO_CLASS_BE, 3))
>>>>>> +#define DEFAULT_MB_OPTIMIZE_SCAN (-1)
>>>>>> +
>>>>>> static const char deprecated_msg[] =
>>>>>> "Mount option \"%s\" will be removed by %s\n"
>>>>>> "Contact linux-ext4@...r.kernel.org if you think we should keep it.\n";
>>>>>> @@ -2008,6 +2011,7 @@ static const struct mount_opts {
>>>>>> {Opt_nombcache, EXT4_MOUNT_NO_MBCACHE, MOPT_SET},
>>>>>> {Opt_prefetch_block_bitmaps, EXT4_MOUNT_PREFETCH_BLOCK_BITMAPS,
>>>>>> MOPT_SET},
>>>>>> + {Opt_mb_optimize_scan, EXT4_MOUNT2_MB_OPTIMIZE_SCAN, MOPT_GTE0},
>>>>>> #ifdef CONFIG_EXT4_DEBUG
>>>>>> {Opt_fc_debug_force, EXT4_MOUNT2_JOURNAL_FAST_COMMIT,
>>>>>> MOPT_SET | MOPT_2 | MOPT_EXT4_ONLY},
>>>>>> @@ -2092,6 +2096,7 @@ static int ext4_set_test_dummy_encryption(struct super_block *sb,
>>>>>> struct ext4_parsed_options {
>>>>>> unsigned long journal_devnum;
>>>>>> unsigned int journal_ioprio;
>>>>>> + int mb_optimize_scan;
>>>>>> };
>>>>>>
>>>>>> static int handle_mount_opt(struct super_block *sb, char *opt, int token,
>>>>>> @@ -2388,6 +2393,13 @@ static int handle_mount_opt(struct super_block *sb, char *opt, int token,
>>>>>> sbi->s_mount_opt |= m->mount_opt;
>>>>>> } else if (token == Opt_data_err_ignore) {
>>>>>> sbi->s_mount_opt &= ~m->mount_opt;
>>>>>> + } else if (token == Opt_mb_optimize_scan) {
>>>>>> + if (arg != 0 && arg != 1) {
>>>>>> + ext4_msg(sb, KERN_WARNING,
>>>>>> + "mb_optimize_scan should be set to 0 or 1.");
>>>>>> + return -1;
>>>>>> + }
>>>>>> + parsed_opts->mb_optimize_scan = arg;
>>>>>> } else {
>>>>>> if (!args->from)
>>>>>> arg = 1;
>>>>>> @@ -4034,6 +4046,7 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
>>>>>> /* Set defaults for the variables that will be set during parsing */
>>>>>> parsed_opts.journal_ioprio = DEFAULT_JOURNAL_IOPRIO;
>>>>>> parsed_opts.journal_devnum = 0;
>>>>>> + parsed_opts.mb_optimize_scan = DEFAULT_MB_OPTIMIZE_SCAN;
>>>>>>
>>>>>> if ((data && !orig_data) || !sbi)
>>>>>> goto out_free_base;
>>>>>> @@ -4984,6 +4997,19 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
>>>>>> ext4_fc_replay_cleanup(sb);
>>>>>>
>>>>>> ext4_ext_init(sb);
>>>>>> +
>>>>>> + /*
>>>>>> + * Enable optimize_scan if number of groups is > threshold. This can be
>>>>>> + * turned off by passing "mb_optimize_scan=0". This can also be
>>>>>> + * turned on forcefully by passing "mb_optimize_scan=1".
>>>>>> + */
>>>>>> + if (parsed_opts.mb_optimize_scan == 1)
>>>>>> + set_opt2(sb, MB_OPTIMIZE_SCAN);
>>>>>> + else if (parsed_opts.mb_optimize_scan == 0)
>>>>>> + clear_opt2(sb, MB_OPTIMIZE_SCAN);
>>>>>> + else if (sbi->s_groups_count >= MB_DEFAULT_LINEAR_SCAN_THRESHOLD)
>>>>>> + set_opt2(sb, MB_OPTIMIZE_SCAN);
>>>>>> +
>>>>>> err = ext4_mb_init(sb);
>>>>>> if (err) {
>>>>>> ext4_msg(sb, KERN_ERR, "failed to initialize mballoc (%d)",
>>>>>> diff --git a/fs/ext4/sysfs.c b/fs/ext4/sysfs.c
>>>>>> index 59ca9d73b42f..16b8a838f631 100644
>>>>>> --- a/fs/ext4/sysfs.c
>>>>>> +++ b/fs/ext4/sysfs.c
>>>>>> @@ -213,6 +213,7 @@ EXT4_RW_ATTR_SBI_UI(mb_order2_req, s_mb_order2_reqs);
>>>>>> EXT4_RW_ATTR_SBI_UI(mb_stream_req, s_mb_stream_request);
>>>>>> EXT4_RW_ATTR_SBI_UI(mb_group_prealloc, s_mb_group_prealloc);
>>>>>> EXT4_RW_ATTR_SBI_UI(mb_max_inode_prealloc, s_mb_max_inode_prealloc);
>>>>>> +EXT4_RW_ATTR_SBI_UI(mb_linear_limit, s_mb_linear_limit);
>>>>>> EXT4_RW_ATTR_SBI_UI(extent_max_zeroout_kb, s_extent_max_zeroout_kb);
>>>>>> EXT4_ATTR(trigger_fs_error, 0200, trigger_test_error);
>>>>>> EXT4_RW_ATTR_SBI_UI(err_ratelimit_interval_ms, s_err_ratelimit_state.interval);
>>>>>> @@ -260,6 +261,7 @@ static struct attribute *ext4_attrs[] = {
>>>>>> ATTR_LIST(mb_stream_req),
>>>>>> ATTR_LIST(mb_group_prealloc),
>>>>>> ATTR_LIST(mb_max_inode_prealloc),
>>>>>> + ATTR_LIST(mb_linear_limit),
>>>>>> ATTR_LIST(max_writeback_mb_bump),
>>>>>> ATTR_LIST(extent_max_zeroout_kb),
>>>>>> ATTR_LIST(trigger_fs_error),
>>>>>> --
>>>>>> 2.31.0.291.g576ba9dcdaf-goog
>>>>>>
>>>>>
>>>>>
>>>>> Cheers, Andreas
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
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