Chao Yu <c...@kernel.org> 于2024年11月20日周三 11:26写道：
>
> On 2024/11/19 16:26, Zhiguo Niu wrote:
> > Chao Yu <c...@kernel.org> 于2024年11月19日周二 15:50写道：
> >>
> >> On 2024/11/19 14:46, Xiuhong Wang wrote:
> >>> 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
> >>
> >> 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?
> > Dear Chao,
> > This patch version aim to shrink extent cache as early as possible on
> > the "all write path"
> > by "write action" -> f2fs_balance_fs -> f2fs_balance_fs_bg
>
> Zhiguo, thanks for explaining again.
>
Dear Chao,
> However, I doubt covering all write paths is not enough, because extent
> node can increase when f2fs_precache_extents() was called from paths
> including fadvise/fiemap/swapon/ioc_precache_extents, and there may be
> no writeback, so we may get no chance to call into f2fs_balance_fs_bg(),
> e.g. there is no data update in mountpoint, or mountpoint is readonly.
yes, Indeed it is.
>
> > As the comment , the "excess_cached_nats" is difficult to achieve in
> > this scenario, and
>
> Another concern is, in high-end products w/ more memory, it may has less
> chance to hit newly added condition in f2fs_balance_fs()? not sure though.
I also agree with this.
There is no other better idea for me(^^) excpetion for the two methods
we discussed above.
any good suggestions ? ^^
thanks！
>
> + if (need && (excess_cached_nats(sbi) ||
> + !f2fs_available_free_memory(sbi, READ_EXTENT_CACHE) ||
> + !f2fs_available_free_memory(sbi, AGE_EXTENT_CACHE)))
>
> I mean will f2fs_available_free_memory(sbi, {READ,AGE}_EXTENT_CACHE)
> return true if available memory is sufficient?
>
> Thanks,
>
> > trigger the issue in path f2fs_write_node_pages->f2fs_balance_fs_bg(is
> > called directly here).
> > At that time, there were already a lot of extent node cnt.
> > Thanks!
> >>
> >>> 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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