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Date: Fri, 14 Aug 2020 11:52:49 +0530
From: Ritesh Harjani <ritesh.list@...il.com>
To: brookxu <brookxu.cn@...il.com>,
Ritesh Harjani <riteshh@...ux.ibm.com>
Cc: adilger.kernel@...ger.ca, tytso@....edu, linux-ext4@...r.kernel.org
Subject: Re: [PATCH v4 2/2] ext4: limit the length of per-inode prealloc list
On 8/14/20 6:41 AM, brookxu wrote:
> Thanks for review this patch :)
>
> Ritesh Harjani wrote on 2020/8/13 21:52:
>> Hi brookxu,
>>
>> Few queries
>>
>> On 8/7/20 2:14 PM, brookxu wrote:
>>> In the scenario of writing sparse files, the Per-inode prealloc list may
>>> be very long, resulting in high overhead for ext4_mb_use_preallocated().
>>> To circumvent this problem, we limit the maximum length of per-inode
>>> prealloc list to 512 and allow users to modify it.
>>>
>>> After patching, we observed that the sys ratio of cpu has dropped, and
>>> the system throughput has increased significantly. We created a process
>>> to write the sparse file, and the running time of the process on the
>>> fixed kernel was significantly reduced, as follows:
>>>
>>> Running time on unfixed kernel：
>>> [root@...CENT64 ~]# time taskset 0x01 ./sparse /data1/sparce.dat
>>> real 0m2.051s
>>> user 0m0.008s
>>> sys 0m2.026s
>>>
>>> Running time on fixed kernel：
>>> [root@...CENT64 ~]# time taskset 0x01 ./sparse /data1/sparce.dat
>>> real 0m0.471s
>>> user 0m0.004s
>>> sys 0m0.395s
>>
>>
>> Please use "--thread" option in your git-format-patch script. So that
>> your patch series comes in a threaded form. It is easier then to apply
>> the series.
>>
>> Somehow I am unable to get my head around how this patch is working.
>> Could you please help explain the theory of operation by answering below
>> queries.
>>
>>>
>>> Signed-off-by: Chunguang Xu <brookxu@...cent.com>
>>> ---
>>> fs/ext4/ext4.h | 3 ++-
>>> fs/ext4/extents.c | 10 ++++----
>>> fs/ext4/file.c | 2 +-
>>> fs/ext4/indirect.c | 2 +-
>>> fs/ext4/inode.c | 6 ++---
>>> fs/ext4/ioctl.c | 2 +-
>>> fs/ext4/mballoc.c | 57 +++++++++++++++++++++++++++++++++++++++++----
>>> fs/ext4/mballoc.h | 4 ++++
>>> fs/ext4/move_extent.c | 4 ++--
>>> fs/ext4/super.c | 2 +-
>>> fs/ext4/sysfs.c | 2 ++
>>> include/trace/events/ext4.h | 14 ++++++-----
>>> 12 files changed, 83 insertions(+), 25 deletions(-)
>>>
>>> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
>>> index 42f5060..68e0ebe 100644
>>> --- a/fs/ext4/ext4.h
>>> +++ b/fs/ext4/ext4.h
>>> @@ -1501,6 +1501,7 @@ struct ext4_sb_info {
>>> unsigned int s_mb_stats;
>>> unsigned int s_mb_order2_reqs;
>>> unsigned int s_mb_group_prealloc;
>>> + unsigned int s_mb_max_inode_prealloc;
>>> unsigned int s_max_dir_size_kb;
>>> /* where last allocation was done - for stream allocation */
>>> unsigned long s_mb_last_group;
>>> @@ -2651,7 +2652,7 @@ extern int ext4_init_inode_table(struct super_block *sb,
>>> extern ext4_fsblk_t ext4_mb_new_blocks(handle_t *,
>>> struct ext4_allocation_request *, int *);
>>> extern int ext4_mb_reserve_blocks(struct super_block *, int);
>>> -extern void ext4_discard_preallocations(struct inode *);
>>> +extern void ext4_discard_preallocations(struct inode *, unsigned int);
>>> extern int __init ext4_init_mballoc(void);
>>> extern void ext4_exit_mballoc(void);
>>> extern void ext4_free_blocks(handle_t *handle, struct inode *inode,
>>> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
>>> index 221f240..a40f928 100644
>>> --- a/fs/ext4/extents.c
>>> +++ b/fs/ext4/extents.c
>>> @@ -100,7 +100,7 @@ static int ext4_ext_trunc_restart_fn(struct inode *inode, int *dropped)
>>> * i_mutex. So we can safely drop the i_data_sem here.
>>> */
>>> BUG_ON(EXT4_JOURNAL(inode) == NULL);
>>> - ext4_discard_preallocations(inode);
>>> + ext4_discard_preallocations(inode, 0);
>>> up_write(&EXT4_I(inode)->i_data_sem);
>>> *dropped = 1;
>>> return 0;
>>> @@ -4272,7 +4272,7 @@ int ext4_ext_map_blocks(handle_t *handle, struct inode *inode,
>>> * not a good idea to call discard here directly,
>>> * but otherwise we'd need to call it every free().
>>> */
>>> - ext4_discard_preallocations(inode);
>>> + ext4_discard_preallocations(inode, 0);
>>> if (flags & EXT4_GET_BLOCKS_DELALLOC_RESERVE)
>>> fb_flags = EXT4_FREE_BLOCKS_NO_QUOT_UPDATE;
>>> ext4_free_blocks(handle, inode, NULL, newblock,
>>> @@ -5299,7 +5299,7 @@ static int ext4_collapse_range(struct inode *inode, loff_t offset, loff_t len)
>>> }
>>>
>>> down_write(&EXT4_I(inode)->i_data_sem);
>>> - ext4_discard_preallocations(inode);
>>> + ext4_discard_preallocations(inode, 0);
>>>
>>> ret = ext4_es_remove_extent(inode, punch_start,
>>> EXT_MAX_BLOCKS - punch_start);
>>> @@ -5313,7 +5313,7 @@ static int ext4_collapse_range(struct inode *inode, loff_t offset, loff_t len)
>>> up_write(&EXT4_I(inode)->i_data_sem);
>>> goto out_stop;
>>> }
>>> - ext4_discard_preallocations(inode);
>>> + ext4_discard_preallocations(inode, 0);
>>>
>>> ret = ext4_ext_shift_extents(inode, handle, punch_stop,
>>> punch_stop - punch_start, SHIFT_LEFT);
>>> @@ -5445,7 +5445,7 @@ static int ext4_insert_range(struct inode *inode, loff_t offset, loff_t len)
>>> goto out_stop;
>>>
>>> down_write(&EXT4_I(inode)->i_data_sem);
>>> - ext4_discard_preallocations(inode);
>>> + ext4_discard_preallocations(inode, 0);
>>>
>>> path = ext4_find_extent(inode, offset_lblk, NULL, 0);
>>> if (IS_ERR(path)) {
>>> diff --git a/fs/ext4/file.c b/fs/ext4/file.c
>>> index 2a01e31..e3ab8ea 100644
>>> --- a/fs/ext4/file.c
>>> +++ b/fs/ext4/file.c
>>> @@ -148,7 +148,7 @@ static int ext4_release_file(struct inode *inode, struct file *filp)
>>> !EXT4_I(inode)->i_reserved_data_blocks)
>>> {
>>> down_write(&EXT4_I(inode)->i_data_sem);
>>> - ext4_discard_preallocations(inode);
>>> + ext4_discard_preallocations(inode, 0);
>>> up_write(&EXT4_I(inode)->i_data_sem);
>>> }
>>> if (is_dx(inode) && filp->private_data)
>>> diff --git a/fs/ext4/indirect.c b/fs/ext4/indirect.c
>>> index be2b66e..ec6b930 100644
>>> --- a/fs/ext4/indirect.c
>>> +++ b/fs/ext4/indirect.c
>>> @@ -696,7 +696,7 @@ static int ext4_ind_trunc_restart_fn(handle_t *handle, struct inode *inode,
>>> * i_mutex. So we can safely drop the i_data_sem here.
>>> */
>>> BUG_ON(EXT4_JOURNAL(inode) == NULL);
>>> - ext4_discard_preallocations(inode);
>>> + ext4_discard_preallocations(inode, 0);
>>> up_write(&EXT4_I(inode)->i_data_sem);
>>> *dropped = 1;
>>> return 0;
>>> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
>>> index 10dd470..bb9e1cd 100644
>>> --- a/fs/ext4/inode.c
>>> +++ b/fs/ext4/inode.c
>>> @@ -383,7 +383,7 @@ void ext4_da_update_reserve_space(struct inode *inode,
>>> */
>>> if ((ei->i_reserved_data_blocks == 0) &&
>>> !inode_is_open_for_write(inode))
>>> - ext4_discard_preallocations(inode);
>>> + ext4_discard_preallocations(inode, 0);
>>> }
>>>
>>> static int __check_block_validity(struct inode *inode, const char *func,
>>> @@ -4056,7 +4056,7 @@ int ext4_punch_hole(struct inode *inode, loff_t offset, loff_t length)
>>> if (stop_block > first_block) {
>>>
>>> down_write(&EXT4_I(inode)->i_data_sem);
>>> - ext4_discard_preallocations(inode);
>>> + ext4_discard_preallocations(inode, 0);
>>>
>>> ret = ext4_es_remove_extent(inode, first_block,
>>> stop_block - first_block);
>>> @@ -4211,7 +4211,7 @@ int ext4_truncate(struct inode *inode)
>>>
>>> down_write(&EXT4_I(inode)->i_data_sem);
>>>
>>> - ext4_discard_preallocations(inode);
>>> + ext4_discard_preallocations(inode, 0);
>>>
>>> if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))
>>> err = ext4_ext_truncate(handle, inode);
>>> diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
>>> index 999cf6a..a5fcc23 100644
>>> --- a/fs/ext4/ioctl.c
>>> +++ b/fs/ext4/ioctl.c
>>> @@ -202,7 +202,7 @@ static long swap_inode_boot_loader(struct super_block *sb,
>>> reset_inode_seed(inode);
>>> reset_inode_seed(inode_bl);
>>>
>>> - ext4_discard_preallocations(inode);
>>> + ext4_discard_preallocations(inode, 0);
>>>
>>> err = ext4_mark_inode_dirty(handle, inode);
>>> if (err < 0) {
>>> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
>>> index 4f21f34..28a139f 100644
>>> --- a/fs/ext4/mballoc.c
>>> +++ b/fs/ext4/mballoc.c
>>> @@ -2736,6 +2736,7 @@ 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_max_inode_prealloc = MB_DEFAULT_MAX_INODE_PREALLOC;
>>> /*
>>> * The default group preallocation is 512, which for 4k block
>>> * sizes translates to 2 megabytes. However for bigalloc file
>>> @@ -4103,7 +4104,7 @@ static void ext4_mb_new_preallocation(struct ext4_allocation_context *ac)
>>> *
>>> * FIXME!! Make sure it is valid at all the call sites
>>> */
>>> -void ext4_discard_preallocations(struct inode *inode)
>>> +void ext4_discard_preallocations(struct inode *inode, unsigned int needed)
>>> {
>>> struct ext4_inode_info *ei = EXT4_I(inode);
>>> struct super_block *sb = inode->i_sb;
>>> @@ -4121,15 +4122,18 @@ void ext4_discard_preallocations(struct inode *inode)
>>>
>>> mb_debug(sb, "discard preallocation for inode %lu\n",
>>> inode->i_ino);
Can we please also add "needed" argument in mb_debug() msg here.
With that feel free to add:
Reviewed-by: Ritesh Harjani <riteshh@...ux.ibm.com>
>>> - trace_ext4_discard_preallocations(inode);
>>> + trace_ext4_discard_preallocations(inode, needed);
>>>
>>> INIT_LIST_HEAD(&list);
>>>
>>> + if (needed == 0)
>>> + needed = UINT_MAX;
>>> +
>>> repeat:
>>> /* first, collect all pa's in the inode */
>>> spin_lock(&ei->i_prealloc_lock);
>>> - while (!list_empty(&ei->i_prealloc_list)) {
>>> - pa = list_entry(ei->i_prealloc_list.next,
>>> + while (!list_empty(&ei->i_prealloc_list) && needed) {
>>> + pa = list_entry(ei->i_prealloc_list.prev,
>>> struct ext4_prealloc_space, pa_inode_list);
>>> BUG_ON(pa->pa_obj_lock != &ei->i_prealloc_lock);
>>> spin_lock(&pa->pa_lock);
>>> @@ -4150,6 +4154,7 @@ void ext4_discard_preallocations(struct inode *inode)
>>> spin_unlock(&pa->pa_lock);
>>> list_del_rcu(&pa->pa_inode_list);
>>> list_add(&pa->u.pa_tmp_list, &list);
>>> + needed--;
>>> continue;
>>> }
>>>
>>> @@ -4549,10 +4554,42 @@ static void ext4_mb_add_n_trim(struct ext4_allocation_context *ac)
>>> }
>>>
>>> /*
>>> + * if per-inode prealloc list is too long, trim some PA
>>> + */
>>> +static void
>>> +ext4_mb_trim_inode_pa(struct inode *inode)
>>> +{
>>> + struct ext4_inode_info *ei = EXT4_I(inode);
>>> + struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
>>> + struct ext4_prealloc_space *pa;
>>> + int count = 0, delta;
>>> +
>>> + rcu_read_lock();
>>> + list_for_each_entry_rcu(pa, &ei->i_prealloc_list, pa_inode_list) {
>>> + spin_lock(&pa->pa_lock);
>>> + if (pa->pa_deleted) {
>>> + spin_unlock(&pa->pa_lock);
>>> + continue;
>>> + }
>>> + count++;
>>> + spin_unlock(&pa->pa_lock);
>>> + }
>>> + rcu_read_unlock();
>>> +
>>> + delta = (sbi->s_mb_max_inode_prealloc >> 2) + 1;
>>> + if (count > sbi->s_mb_max_inode_prealloc + delta) {
>>> + count -= sbi->s_mb_max_inode_prealloc;
>>> + ext4_discard_preallocations(inode, count);
>>> + }
>>> +}
>>> +
>>> +/*
>>> * release all resource we used in allocation
>>> */
>>> static int ext4_mb_release_context(struct ext4_allocation_context *ac)
>>> {
>>> + struct inode *inode = ac->ac_inode;
>>> + struct ext4_inode_info *ei = EXT4_I(inode);
>>> struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
>>> struct ext4_prealloc_space *pa = ac->ac_pa;
>>> if (pa) {
>>> @@ -4578,6 +4615,17 @@ static int ext4_mb_release_context(struct ext4_allocation_context *ac)
>>> ext4_mb_add_n_trim(ac);
>>> }
>>> }
>>> +
>>> + if (pa->pa_type == MB_INODE_PA) {
>>> + /*
>>> + * treat per-inode prealloc list as a lru list, then try
>>> + * to trim the least recently used PA.
>>> + */
>>> + spin_lock(pa->pa_obj_lock);
>>> + list_move(&ei->i_prealloc_list, &pa->pa_inode_list);
>>
>> So what you are doing here is essentially moving back ei->i_prealloc_list back into pa->pa_inode_lis
>
> The operation here uses LRU to maintain the prealloc list, so we can trim the least recently used PA
> from the tail of the list. According to the principle of locality, this may reduce the impact on the
> program.
>
>> Then in ext4_mb_trim_inode_pa(), it will traverse over i_prealloc_list
>> which is empty anyways no? (considering single threaded write here).
>> I am definitely missing something, could you help explain how is it
>> getting trimmed then?
>
Sorry, I had got confused here with something else. This looks fine to
me now :)
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