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AJvYcCWIfQdr4VHcyjRrIGYlmAc7yAx8bH3TUVU4Nhh83S97fr5Ho62Muqtr83BKnM3S/OpXAkMQkH6CECGJRaI=@vger.kernel.org X-Gm-Message-State: AOJu0Yx5X5aY0HJo6iCEZA+7wjz4nadBXztaRyWqmzRWONKXng24L0zc BvRClEYYuysqwNK2Ek5U40E0mWtFQy34zqEgmjBKQoflYdnT54eWo1JJNYzVCJDNSUalYmCoZAd Wkxde6/22CTOAVbAS8dpclQQrk1Q= X-Google-Smtp-Source: AGHT+IFzSjc9vFJGGEdMyChIRwyrY50Xv9jtOnG9bmyOyAJKGCmdRAeb3y9enjfoi3BCUpLNAGyZ5JiN0qnwiQtBD+8= X-Received: by 2002:a05:6000:400b:b0:382:4538:c0d with SMTP id ffacd0b85a97d-38245380e2bmr2127655f8f.2.1732004789635; Tue, 19 Nov 2024 00:26:29 -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> In-Reply-To: <5b0c17da-f1e1-490d-a560-3312bc8c3247@kernel.org> From: Zhiguo Niu Date: Tue, 19 Nov 2024 16:26:18 +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=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 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 =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, bo= ol 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) > >>> 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, bo= ol 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_CA= CHE) || > >>> + !f2fs_available_free_memory(sbi, AGE_EXTENT_CAC= HE))) > >> > >> 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(st= ruct inode *inode, > >> } > >> > >> static unsigned int __free_extent_tree(struct f2fs_sb_info *sbi, > >> - struct extent_tree *et) > >> + struct extent_tree *et, unsigned int n= r_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 f2fs= _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 inod= e *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 f2= fs_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_cn= t); > >> 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 =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 *ino= de, 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 p= rocess. > > 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 As the comment , the "excess_cached_nats" is difficult to achieve in this scenario, and 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+0xc8/0= x168) > > [H 103098.974425] c2 [] > > (f2fs_update_extent_tree_range+0x4a0/0x724) > > [H 103098.974459] c2 [] (f2fs_update_extent_cache+0x1= 9c/0x1b0) > > [H 103098.974495] c2 [] (f2fs_outplace_write_data+0x7= 4/0xf0) > > [H 103098.974525] c2 [] (f2fs_do_write_data_page+0x3e= 4/0x6c8) > > [H 103098.974552] c2 [] > > (f2fs_write_single_data_page+0x478/0xab0) > > [H 103098.974574] c2 [] (f2fs_write_cache_pages+0x454= /0xaac) > > [H 103098.974596] c2 [] (__f2fs_write_data_pages+0x40= c/0x4f0) > > [H 103098.974617] c2 [] (f2fs_write_data_pages+0x30/0= x40) > > [H 103098.974645] c2 [] (do_writepages+0x18c/0x3e8) > > [H 103098.974678] c2 [] (__writeback_single_inode+0x4= 8/0x498) > > [H 103098.974720] c2 [] (writeback_sb_inodes+0x454/0x= 9b0) > > [H 103098.974754] c2 [] (__writeback_inodes_wb+0x198/= 0x224) > > [H 103098.974788] c2 [] (wb_writeback+0x1c0/0x698) > > [H 103098.974819] c2 [] (wb_do_writeback+0x420/0x54c) > > [H 103098.974853] c2 [] (wb_workfn+0xe4/0x388) >