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 C44CDE571 for ; Tue, 19 Nov 2024 06:05:49 +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=1731996349; cv=none; b=n+klCfCnVOURwv/+4MsVmGqXxhttHUhYo6Cx15zigvuVZLU21lTHlJ/KALaWb9VKnUNJqVjC+QfsZT+38qK+bCLIM1ue8CWisPH/yK23xtj8EysrSQQuprm8kdxPxuQdbCDHdSE3vqcvJPI1MktwjZlXUXNWEXWfzblvV4PCX3U= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1731996349; c=relaxed/simple; bh=xePXyP7ebkzzCGKOqeQWr1/POG8ku3mwGPWZLIRUfT8=; h=Message-ID:Date:MIME-Version:Cc:Subject:To:References:From: In-Reply-To:Content-Type; b=uJE2RZcsq9Qey2/1eNsw8UTnl+/uKexNmsQXMKsc7YLFj+DJ+rGz4kvgwkv1icOTb8jXcUz5wJ6TsE2gZ5qtjmCo4FIKS5ZgCCGxsZTjyU4au4yEc7LcmiaZrCOLEuoM8eNDWVMu3G7oON0ZtADsJ6HRlwga1m8BWPpQ+ciUqxc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=rCOOqkwY; 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="rCOOqkwY" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 757D1C4CEDA; Tue, 19 Nov 2024 06:05:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1731996349; bh=xePXyP7ebkzzCGKOqeQWr1/POG8ku3mwGPWZLIRUfT8=; h=Date:Cc:Subject:To:References:From:In-Reply-To:From; b=rCOOqkwYrEUm53qH7CqYpO+pmH/EjVjdmQumHb7WrO+WsUSS0Xq/Ko2aNsLHMcruT P8vcTkgQGcDiu2F2HCh+0ITjFViGiVnMQds32AZa9EqYVpj0GI2voGk22OwMLWpwo7 yiwNC1nYCZ9rwGskwj6dY5iEifgKesxCkv826rq8CC8VptQ2i/qnbNCC/IkqZanHH9 Y0gnxsLdj5jIm+ODME7gk9/QucRpxUxD545FiT7rYgz/QD3gNqxH4mHjHOnOrIo4eZ 48HN3oyk7P58nVz3syrfFA3yuMpUBmhj5fel2mBFzNzY/o9QMyqzfE3hRJrBYts4V9 +lrVZDqpiOyxA== Message-ID: Date: Tue, 19 Nov 2024 14:05:45 +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 , niuzhiguo84@gmail.com, xiuhong.wang.cn@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 , jaegeuk@kernel.org, linux-f2fs-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org References: <20241112110627.1314632-1-xiuhong.wang@unisoc.com> Content-Language: en-US From: Chao Yu In-Reply-To: <20241112110627.1314632-1-xiuhong.wang@unisoc.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit 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))