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 9182840BE5 for ; Wed, 20 Nov 2024 03:26:49 +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=1732073209; cv=none; b=PnZ63HmvOHyynrEzSD6aYRfSdfuL1czZ1m4o9Js4A95rZ7wUPxTEprJ08rLFMPUtZAPKn1S11zsT3CmAgwv2j0E7FIHvap+yU+efLjXmEz4Y+HM4hC6VUmrIjiJCR9dFXtIdfcTnLobwe68W0QQMjZWIE57NMaq/YxQxC3Mwlas= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732073209; c=relaxed/simple; bh=pFoFdpRUSILZfAVqihjYwl6kJm2IBX+bSl5vNZz/tRw=; h=Message-ID:Date:MIME-Version:Cc:Subject:To:References:From: In-Reply-To:Content-Type; b=Nj/gTgm9LD1wx2NUdsFzTQ2Fe2QXQ/pFpwF0OcBf5bdGHL85oxfAdUB/MbhYcPvlYElLfHr1bLf45lhwqmUTUpgs+Hx8bWVLPillCuGeZCHByBmFEPfdoz8LlNGTfDrCnzohD/y94Wbtjn6j0Z3tM2vcoLXzdN75m5e7yF2WMeo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=CM8WD1Z1; 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="CM8WD1Z1" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8B927C4CECD; Wed, 20 Nov 2024 03:26:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1732073209; bh=pFoFdpRUSILZfAVqihjYwl6kJm2IBX+bSl5vNZz/tRw=; h=Date:Cc:Subject:To:References:From:In-Reply-To:From; b=CM8WD1Z1qWye61kU1FEj875V+2M6S6c9RvKVkzXsCYVVm1eVztqMQkw9iYKVeN/6d zDwQrUoQs+z4wbUXbjH9P8FY0b1lKrGks80r2GayN8+Cl30J1Op0fx/fFfj9QBLoH3 JXDbbVWjnyJ9cNGao8vRV2UtFabBIcUWAQYNxwp4oxYDpFY6lXITDffecieh/gKCWJ 7lHY0kYMe14uOwSMJErXUTk8hUCZAwAPNKRWtRtGqRT8W2GsAgivyMlTO5EELZB2gZ ATdBAmLvLDanslNiUvAdbmOwzAdq+C1sWjtzy3IMZaJA85hLUXfZUkPrXzuFJMT73h wbYbUlP7npKgw== Message-ID: <65b89566-1038-4422-9e2e-4d7da26dd1c7@kernel.org> Date: Wed, 20 Nov 2024 11:26:44 +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 , 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 Subject: Re: [PATCH] f2fs: Fix to avoid long time to shrink extent cache To: Zhiguo Niu References: <20241112110627.1314632-1-xiuhong.wang@unisoc.com> <5b0c17da-f1e1-490d-a560-3312bc8c3247@kernel.org> 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 16:26, Zhiguo Niu wrote: > Chao Yu 于2024年11月19日周二 15:50写道： >> >> 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? > 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. 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. > 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. + 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+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) >>