Chao Yu <c...@kernel.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.w...@unisoc.com>
> > Signed-off-by: Zhiguo Niu <zhiguo....@unisoc.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
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:
[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)
_______________________________________________
Linux-f2fs-devel mailing list
Linux-f2fs-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
