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Message-ID: <5b0c17da-f1e1-490d-a560-3312bc8c3247@kernel.org>
Date: Tue, 19 Nov 2024 15:50:35 +0800
From: Chao Yu <chao@...nel.org>
To: Xiuhong Wang <xiuhong.wang.cn@...il.com>
Cc: Chao Yu <chao@...nel.org>, Xiuhong Wang <xiuhong.wang@...soc.com>,
jaegeuk@...nel.org, linux-f2fs-devel@...ts.sourceforge.net,
linux-kernel@...r.kernel.org, niuzhiguo84@...il.com,
hao_hao.wang@...soc.com, ke.wang@...soc.com
Subject: Re: [PATCH] f2fs: Fix to avoid long time to shrink extent cache
On 2024/11/19 14:46, Xiuhong Wang wrote:
> Chao Yu <chao@...nel.org> 于2024年11月19日周二 14:05写道：
>>
>> On 2024/11/12 19:06, Xiuhong Wang wrote:
>>> We encountered a system hang problem based on the following
>>> experiment:
>>> There are 17 processes, 8 of which do 4k data read, write and
>>> compare tests, and 8 do 64k read, write and compare tests. Each
>>> thread writes a 256M file, and another thread writes a large file
>>> to 80% of the disk, and then keeps doing read operations, all of
>>> which are direct operations. This will cause the large file to be
>>> filled to 80% of the disk to be severely fragmented. On a 512GB
>>> device, this large file may generate a huge zombie extent tree.
>>>
>>> When system shutting down, the init process needs to wait for the
>>> writeback process, and the writeback process may encounter the
>>> situation where the READ_EXTENT_CACHE space is insufficient and
>>> needs to free the zombie extent tree. The extent tree has a large
>>> number of extent nodes, it will a long free time to free, which
>>> triggers system hang.
>> > > The stack when the problem occurs is as follows:
>>> crash_arm64> bt 1
>>> PID: 1 TASK: ffffff80801a9200 CPU: 1 COMMAND: "init"
>>> #0 [ffffffc00806b9a0] __switch_to at ffffffc00810711c
>>> #1 [ffffffc00806ba00] __schedule at ffffffc0097c1c4c
>>> #2 [ffffffc00806ba60] schedule at ffffffc0097c2308
>>> #3 [ffffffc00806bab0] wb_wait_for_completion at ffffffc0086320d4
>>> #4 [ffffffc00806bb20] writeback_inodes_sb at ffffffc00863719c
>>> #5 [ffffffc00806bba0] sync_filesystem at ffffffc00863c98c
>>> #6 [ffffffc00806bbc0] f2fs_quota_off_umount at ffffffc00886fc60
>>> #7 [ffffffc00806bc20] f2fs_put_super at ffffffc0088715b4
>>> #8 [ffffffc00806bc60] generic_shutdown_super at ffffffc0085cd61c
>>> #9 [ffffffc00806bcd0] kill_f2fs_super at ffffffc00886b3dc
>>>
>>> crash_arm64> bt 14997
>>> PID: 14997 TASK: ffffff8119d82400 CPU: 3 COMMAND: "kworker/u16:0"
>>> #0 [ffffffc019f8b760] __detach_extent_node at ffffffc0088d5a58
>>> #1 [ffffffc019f8b790] __release_extent_node at ffffffc0088d5970
>>> #2 [ffffffc019f8b810] f2fs_shrink_extent_tree at ffffffc0088d5c7c
>>> #3 [ffffffc019f8b8a0] f2fs_balance_fs_bg at ffffffc0088c109c
>>> #4 [ffffffc019f8b910] f2fs_write_node_pages at ffffffc0088bd4d8
>>> #5 [ffffffc019f8b990] do_writepages at ffffffc0084a0b5c
>>> #6 [ffffffc019f8b9f0] __writeback_single_inode at ffffffc00862ee28
>>> #7 [ffffffc019f8bb30] writeback_sb_inodes at ffffffc0086358c0
>>> #8 [ffffffc019f8bc10] wb_writeback at ffffffc0086362dc
>>> #9 [ffffffc019f8bcc0] wb_do_writeback at ffffffc008634910
>>>
>>> Process 14997 ran for too long and caused the system hang.
>>>
>>> At this time, there are still 1086911 extent nodes in this zombie
>>> extent tree that need to be cleaned up.
>>>
>>> crash_arm64_sprd_v8.0.3++> extent_tree.node_cnt ffffff80896cc500
>>> node_cnt = {
>>> counter = 1086911
>>> },
>>>
>>> The root cause of this problem is that when the f2fs_balance_fs
>>> function is called in the write process, it will determine
>>> whether to call f2fs_balance_fs_bg, but it is difficult to
>>> meet the condition of excess_cached_nats. When the
>>> f2fs_shrink_extent_tree function is called to free during
>>> f2fs_write_node_pages, there are too many extent nodes on the
>>> extent tree, which causes a loop and causes a system hang.
>>>
>>> To solve this problem, when calling f2fs_balance_fs, check whether
>>> the extent cache is sufficient. If not, release the zombie extent
>>> tree.
>>>
>>> Signed-off-by: Xiuhong Wang <xiuhong.wang@...soc.com>
>>> Signed-off-by: Zhiguo Niu <zhiguo.niu@...soc.com>
>>> ---
>>> Test the problem with the temporary versions:
>>> patch did not reproduce the problem, the patch is as follows:
>>> @@ -415,7 +415,7 @@ void f2fs_balance_fs(struct f2fs_sb_info *sbi, bool need)
>>> f2fs_stop_checkpoint(sbi, false, STOP_CP_REASON_FAULT_INJECT);
>>>
>>> /* balance_fs_bg is able to be pending */
>>> - if (need && excess_cached_nats(sbi))
>>> + if (need)
>>> f2fs_balance_fs_bg(sbi, false);
>>>
>>> ---
>>> fs/f2fs/segment.c | 4 +++-
>>> 1 file changed, 3 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>>> index 1766254279d2..390bec177567 100644
>>> --- a/fs/f2fs/segment.c
>>> +++ b/fs/f2fs/segment.c
>>> @@ -415,7 +415,9 @@ void f2fs_balance_fs(struct f2fs_sb_info *sbi, bool need)
>>> f2fs_stop_checkpoint(sbi, false, STOP_CP_REASON_FAULT_INJECT);
>>>
>>> /* balance_fs_bg is able to be pending */
>>> - if (need && excess_cached_nats(sbi))
>>> + if (need && (excess_cached_nats(sbi) ||
>>> + !f2fs_available_free_memory(sbi, READ_EXTENT_CACHE) ||
>>> + !f2fs_available_free_memory(sbi, AGE_EXTENT_CACHE)))
>>
>> Hi,
>>
>> I doubt if there is no enough memory, we may still run into
>> f2fs_shrink_extent_tree() and suffer such long time delay.
>>
>> So, can we just let __free_extent_tree() break the loop once we have
>> released entries w/ target number? something like this:
>>
>> ---
>> fs/f2fs/extent_cache.c | 15 ++++++++++-----
>> 1 file changed, 10 insertions(+), 5 deletions(-)
>>
>> diff --git a/fs/f2fs/extent_cache.c b/fs/f2fs/extent_cache.c
>> index 019c1f7b7fa5..38c71c1c4fb7 100644
>> --- a/fs/f2fs/extent_cache.c
>> +++ b/fs/f2fs/extent_cache.c
>> @@ -379,11 +379,12 @@ static struct extent_tree *__grab_extent_tree(struct inode *inode,
>> }
>>
>> static unsigned int __free_extent_tree(struct f2fs_sb_info *sbi,
>> - struct extent_tree *et)
>> + struct extent_tree *et, unsigned int nr_shrink)
>> {
>> struct rb_node *node, *next;
>> struct extent_node *en;
>> unsigned int count = atomic_read(&et->node_cnt);
>> + unsigned int i = 0;
>>
>> node = rb_first_cached(&et->root);
>> while (node) {
>> @@ -391,6 +392,9 @@ static unsigned int __free_extent_tree(struct f2fs_sb_info *sbi,
>> en = rb_entry(node, struct extent_node, rb_node);
>> __release_extent_node(sbi, et, en);
>> node = next;
>> +
>> + if (nr_shrink && ++i >= nr_shrink)
>> + break;
>> }
>>
>> return count - atomic_read(&et->node_cnt);
>> @@ -761,7 +765,7 @@ static void __update_extent_tree_range(struct inode *inode,
>> }
>>
>> if (is_inode_flag_set(inode, FI_NO_EXTENT))
>> - __free_extent_tree(sbi, et);
>> + __free_extent_tree(sbi, et, 0);
>>
>> if (et->largest_updated) {
>> et->largest_updated = false;
>> @@ -942,7 +946,8 @@ static unsigned int __shrink_extent_tree(struct f2fs_sb_info *sbi, int nr_shrink
>> list_for_each_entry_safe(et, next, &eti->zombie_list, list) {
>> if (atomic_read(&et->node_cnt)) {
>> write_lock(&et->lock);
>> - node_cnt += __free_extent_tree(sbi, et);
>> + node_cnt += __free_extent_tree(sbi, et,
>> + nr_shrink - node_cnt - tree_cnt);
>> write_unlock(&et->lock);
>> }
>> f2fs_bug_on(sbi, atomic_read(&et->node_cnt));
>> @@ -1095,7 +1100,7 @@ static unsigned int __destroy_extent_node(struct inode *inode,
>> return 0;
>>
>> write_lock(&et->lock);
>> - node_cnt = __free_extent_tree(sbi, et);
>> + node_cnt = __free_extent_tree(sbi, et, 0);
>> write_unlock(&et->lock);
>>
>> return node_cnt;
>> @@ -1117,7 +1122,7 @@ static void __drop_extent_tree(struct inode *inode, enum extent_type type)
>> return;
>>
>> write_lock(&et->lock);
>> - __free_extent_tree(sbi, et);
>> + __free_extent_tree(sbi, et, 0);
>> if (type == EX_READ) {
>> set_inode_flag(inode, FI_NO_EXTENT);
>> if (et->largest.len) {
>> --
>> 2.40.1
>>
>> Thanks,
>>
>>> f2fs_balance_fs_bg(sbi, false);
>>>
>>> if (!f2fs_is_checkpoint_ready(sbi))
>>
>
>
> Hi chao,
>
> We have also considered this approach, but the problem still occurs
> after retesting.
> 1. The problem still occurs in the following call of the unmount data process.
> f2fs_put_super -> f2fs_leave_shrinker
Yes, I guess we need to fix this path as well, however, your patch didn't
cover this path as well, am I missing something?
> 2. Writing back the inode in the normal write-back process will
> release the extent cache, and the problem still occurs. The stack is
> as follows:
Ditto,
Thanks,
> [H 103098.974356] c2 [<ffffffc008aee8a4>] (rb_erase+0x204/0x334)
> [H 103098.974389] c2 [<ffffffc0088f8fd0>] (__release_extent_node+0xc8/0x168)
> [H 103098.974425] c2 [<ffffffc0088fad74>]
> (f2fs_update_extent_tree_range+0x4a0/0x724)
> [H 103098.974459] c2 [<ffffffc0088fa8c0>] (f2fs_update_extent_cache+0x19c/0x1b0)
> [H 103098.974495] c2 [<ffffffc0088edc70>] (f2fs_outplace_write_data+0x74/0xf0)
> [H 103098.974525] c2 [<ffffffc0088ca834>] (f2fs_do_write_data_page+0x3e4/0x6c8)
> [H 103098.974552] c2 [<ffffffc0088cb150>]
> (f2fs_write_single_data_page+0x478/0xab0)
> [H 103098.974574] c2 [<ffffffc0088d0bd0>] (f2fs_write_cache_pages+0x454/0xaac)
> [H 103098.974596] c2 [<ffffffc0088d0698>] (__f2fs_write_data_pages+0x40c/0x4f0)
> [H 103098.974617] c2 [<ffffffc0088cc860>] (f2fs_write_data_pages+0x30/0x40)
> [H 103098.974645] c2 [<ffffffc0084c0e00>] (do_writepages+0x18c/0x3e8)
> [H 103098.974678] c2 [<ffffffc0086503cc>] (__writeback_single_inode+0x48/0x498)
> [H 103098.974720] c2 [<ffffffc0086562c8>] (writeback_sb_inodes+0x454/0x9b0)
> [H 103098.974754] c2 [<ffffffc008655de8>] (__writeback_inodes_wb+0x198/0x224)
> [H 103098.974788] c2 [<ffffffc008656d0c>] (wb_writeback+0x1c0/0x698)
> [H 103098.974819] c2 [<ffffffc008655614>] (wb_do_writeback+0x420/0x54c)
> [H 103098.974853] c2 [<ffffffc008654f50>] (wb_workfn+0xe4/0x388)
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