From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 397A46E2BE for ; Tue, 19 Nov 2024 07:50:39 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732002640; cv=none; b=AeanE3vfIuEMRkCvPE0xoy8hwG/CZBohom4yf+zDSTUefBA4KVxJ+/k6JnTKjkaGlpVhSwzrf0mRn9j2DkKBb2/3xgZUbCbe/tN7HdBLXsyHDjDhDwtRtuUEit4lys5j0Fugop55L8gsD0lG8Yb8zsj24+olJNvY2sOM+107mSc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732002640; c=relaxed/simple; bh=gbF36eMx9sfuMRVW+aFk+4froAkv7fnorpos7XgT+ds=; h=Message-ID:Date:MIME-Version:Cc:Subject:To:References:From: In-Reply-To:Content-Type; b=MXgwnzGiGKHD7tor25td4pNP+jjY3ICb3zG8y8hCUh786XHL/jpTCsghjN+alrXTDZYmwI7HMEnHrScPMklmb7yX+hbM1bybyZMbiny5eK3jWiigal1ZvtfmYO3xQJpK64R8k/7cZnE9vuEpmhptugJAClyLgupocE6s28XF7jk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=vLLw8dhY; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="vLLw8dhY" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D3365C4CECF; Tue, 19 Nov 2024 07:50:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1732002639; bh=gbF36eMx9sfuMRVW+aFk+4froAkv7fnorpos7XgT+ds=; h=Date:Cc:Subject:To:References:From:In-Reply-To:From; b=vLLw8dhY+Vk58xmDLpY9ZI3iIdLqh8G26R4HqkBHQLu2etn15x2J/+XaKYJToEjSD 9NC6rQObOopwcSbPlxAnSWGPZMkUNA+90ij9ryXP23ERkL/H/dy0sNTL8YW5TFUEI/ ZB4l8fW6IlSMKV+n8NbPjqSFaPfuPY5YerUlUpw+P4jYk4XgITl9XsKucgEfFnGFBr ool+wGiDm+Hx5qlMLJIe8YGceXAfIwImyYrsTcpi/RKJlr7kt/ocOyDHq+Lj+1+egZ ZjK8yuvZQIRGnNqmopKTCAvoPhk+APSwPeDzfRehCdq7y/D2/Hct+JjPNUDQ7Gk7cm MK5D2D2tqh16A== Message-ID: <5b0c17da-f1e1-490d-a560-3312bc8c3247@kernel.org> Date: Tue, 19 Nov 2024 15:50:35 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Cc: Chao Yu , Xiuhong Wang , jaegeuk@kernel.org, linux-f2fs-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org, niuzhiguo84@gmail.com, hao_hao.wang@unisoc.com, ke.wang@unisoc.com Subject: Re: [PATCH] f2fs: Fix to avoid long time to shrink extent cache To: Xiuhong Wang References: <20241112110627.1314632-1-xiuhong.wang@unisoc.com> Content-Language: en-US From: Chao Yu In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 2024/11/19 14:46, Xiuhong Wang wrote: > Chao Yu 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 >>> 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_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? > 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+0x19c/0x1b0) > [H 103098.974495] c2 [] (f2fs_outplace_write_data+0x74/0xf0) > [H 103098.974525] c2 [] (f2fs_do_write_data_page+0x3e4/0x6c8) > [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+0x40c/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+0x48/0x498) > [H 103098.974720] c2 [] (writeback_sb_inodes+0x454/0x9b0) > [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)