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AJvYcCUXZbSJjr95NbIPsG/xeH67xbTJeHdyFNLOf1Fx1T6cjZnvlaIz0nKzAsSD4LL3B3liGIgv9PSDVhuF6MI=@vger.kernel.org X-Gm-Message-State: AOJu0Ywg7yHP8fDJz2Ae2bkzwpeiV6TWw7IYYQgrhQsODgLlQq50Fzuf KVIdjbmH5xUoH3BtEak6kK6bpEf2XxNnNp3ZQBxWJ8Mfr+RPz8l/1oigkZO/n9RSGj8GK1mjdBo 1lzj9yhG20SIe7s9Fsy7jhxVmsCt8PIUi X-Gm-Gg: ASbGncsM9tCDbsdkiELfvpnfs+xSMJ4JOLA8aLnonGnqdR/ud9pg6uU3NtOnyL4/2zy Px3NUWd8sN6Lx59BXA1ABVKy2nC8tNvSx X-Google-Smtp-Source: AGHT+IE9+fNqB3SD6B9SB2D58HneDXUTUgLp0Tb82wQov+6QPMa5SWYo9vyiur1mNcuOmisug9kvv2GBX4byYbrmC5g= X-Received: by 2002:a05:6000:2a5:b0:382:42c3:83f7 with SMTP id ffacd0b85a97d-38254b0f088mr359036f8f.10.1732081535048; Tue, 19 Nov 2024 21:45:35 -0800 (PST) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 References: <20241112110627.1314632-1-xiuhong.wang@unisoc.com> <5b0c17da-f1e1-490d-a560-3312bc8c3247@kernel.org> <65b89566-1038-4422-9e2e-4d7da26dd1c7@kernel.org> In-Reply-To: <65b89566-1038-4422-9e2e-4d7da26dd1c7@kernel.org> From: Zhiguo Niu Date: Wed, 20 Nov 2024 13:45:23 +0800 Message-ID: Subject: Re: [PATCH] f2fs: Fix to avoid long time to shrink extent cache To: Chao Yu Cc: Xiuhong Wang , Xiuhong Wang , jaegeuk@kernel.org, linux-f2fs-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org, hao_hao.wang@unisoc.com, ke.wang@unisoc.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Chao Yu =E4=BA=8E2024=E5=B9=B411=E6=9C=8820=E6=97=A5=E5= =91=A8=E4=B8=89 11:26=E5=86=99=E9=81=93=EF=BC=9A > > On 2024/11/19 16:26, Zhiguo Niu wrote: > > Chao Yu =E4=BA=8E2024=E5=B9=B411=E6=9C=8819=E6=97=A5= =E5=91=A8=E4=BA=8C 15:50=E5=86=99=E9=81=93=EF=BC=9A > >> > >> On 2024/11/19 14:46, Xiuhong Wang wrote: > >>> Chao Yu =E4=BA=8E2024=E5=B9=B411=E6=9C=8819=E6=97= =A5=E5=91=A8=E4=BA=8C 14:05=E5=86=99=E9=81=93=EF=BC=9A > >>>> > >>>> 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 ffffffc0086320d= 4 > >>>>> #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 ffffffc0085cd61= c > >>>>> #9 [ffffffc00806bcd0] kill_f2fs_super at ffffffc00886b3dc > >>>>> > >>>>> crash_arm64> bt 14997 > >>>>> PID: 14997 TASK: ffffff8119d82400 CPU: 3 COMMAND: "kworker/u= 16:0" > >>>>> #0 [ffffffc019f8b760] __detach_extent_node at ffffffc0088d5a58 > >>>>> #1 [ffffffc019f8b790] __release_extent_node at ffffffc0088d5970 > >>>>> #2 [ffffffc019f8b810] f2fs_shrink_extent_tree at ffffffc0088d5c= 7c > >>>>> #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 ffffffc00862e= e28 > >>>>> #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 =3D { > >>>>> counter =3D 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 > >>>>> Signed-off-by: Zhiguo Niu > >>>>> --- > >>>>> 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_FAU= LT_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_C= ACHE))) > >>>> > >>>> 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 =3D atomic_read(&et->node_cnt); > >>>> + unsigned int i =3D 0; > >>>> > >>>> node =3D rb_first_cached(&et->root); > >>>> while (node) { > >>>> @@ -391,6 +392,9 @@ static unsigned int __free_extent_tree(struct f2= fs_sb_info *sbi, > >>>> en =3D rb_entry(node, struct extent_node, rb_node)= ; > >>>> __release_extent_node(sbi, et, en); > >>>> node =3D next; > >>>> + > >>>> + if (nr_shrink && ++i >=3D nr_shrink) > >>>> + break; > >>>> } > >>>> > >>>> return count - atomic_read(&et->node_cnt); > >>>> @@ -761,7 +765,7 @@ static void __update_extent_tree_range(struct in= ode *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 =3D 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 +=3D __free_extent_tree(sbi, et); > >>>> + node_cnt +=3D __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(stru= ct inode *inode, > >>>> return 0; > >>>> > >>>> write_lock(&et->lock); > >>>> - node_cnt =3D __free_extent_tree(sbi, et); > >>>> + node_cnt =3D __free_extent_tree(sbi, et, 0); > >>>> write_unlock(&et->lock); > >>>> > >>>> return node_cnt; > >>>> @@ -1117,7 +1122,7 @@ static void __drop_extent_tree(struct inode *i= node, enum extent_type type) > >>>> return; > >>>> > >>>> write_lock(&et->lock); > >>>> - __free_extent_tree(sbi, et); > >>>> + __free_extent_tree(sbi, et, 0); > >>>> if (type =3D=3D 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 did= n'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=EF=BC=81 > > + 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 [] (rb_erase+0x204/0x334) > >>> [H 103098.974389] c2 [] (__release_extent_node+0xc8= /0x168) > >>> [H 103098.974425] c2 [] > >>> (f2fs_update_extent_tree_range+0x4a0/0x724) > >>> [H 103098.974459] c2 [] (f2fs_update_extent_cache+0= x19c/0x1b0) > >>> [H 103098.974495] c2 [] (f2fs_outplace_write_data+0= x74/0xf0) > >>> [H 103098.974525] c2 [] (f2fs_do_write_data_page+0x= 3e4/0x6c8) > >>> [H 103098.974552] c2 [] > >>> (f2fs_write_single_data_page+0x478/0xab0) > >>> [H 103098.974574] c2 [] (f2fs_write_cache_pages+0x4= 54/0xaac) > >>> [H 103098.974596] c2 [] (__f2fs_write_data_pages+0x= 40c/0x4f0) > >>> [H 103098.974617] c2 [] (f2fs_write_data_pages+0x30= /0x40) > >>> [H 103098.974645] c2 [] (do_writepages+0x18c/0x3e8) > >>> [H 103098.974678] c2 [] (__writeback_single_inode+0= x48/0x498) > >>> [H 103098.974720] c2 [] (writeback_sb_inodes+0x454/= 0x9b0) > >>> [H 103098.974754] c2 [] (__writeback_inodes_wb+0x19= 8/0x224) > >>> [H 103098.974788] c2 [] (wb_writeback+0x1c0/0x698) > >>> [H 103098.974819] c2 [] (wb_do_writeback+0x420/0x54= c) > >>> [H 103098.974853] c2 [] (wb_workfn+0xe4/0x388) > >> >