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Date: Thu, 13 Aug 2020 19:22:53 +0530
From: Ritesh Harjani <riteshh@...ux.ibm.com>
To: brookxu <brookxu.cn@...il.com>, adilger.kernel@...ger.ca,
"Theodore Y. Ts'o" <tytso@....edu>
Cc: linux-ext4@...r.kernel.org
Subject: Re: [PATCH v4 2/2] ext4: limit the length of per-inode prealloc list
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);
> - 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_list.
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?
and how are you adding it back to ext4_inode_info->i_prealloc_list
which is traversed to check if we can use pe-existing preallocation
of an inode in ext4_mb_use_preallocated(ac)
> + spin_unlock(pa->pa_obj_lock);
> + }
> +
> ext4_mb_put_pa(ac, ac->ac_sb, pa);
> }
> if (ac->ac_bitmap_page)
> @@ -4587,6 +4635,7 @@ static int ext4_mb_release_context(struct ext4_allocation_context *ac)
> if (ac->ac_flags & EXT4_MB_HINT_GROUP_ALLOC)
> mutex_unlock(&ac->ac_lg->lg_mutex);
> ext4_mb_collect_stats(ac);
> + ext4_mb_trim_inode_pa(inode);
> return 0;
> }
>
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