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Message-ID: <fb436fdb-a4eb-49cc-a730-354611e88b21@kernel.org>
Date: Tue, 19 Nov 2024 14:05:45 +0800
From: Chao Yu <chao@...nel.org>
To: Xiuhong Wang <xiuhong.wang@...soc.com>, jaegeuk@...nel.org,
linux-f2fs-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Cc: Chao Yu <chao@...nel.org>, niuzhiguo84@...il.com,
xiuhong.wang.cn@...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 2024/11/12 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))
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