linux-kernel - Re: [PATCH v3] f2fs: fix out-of-free problem caused by atomic write

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Message-ID: <54e2f05e-f5be-68ac-9115-0c70ab6c8082@huawei.com>
Date:   Tue, 7 Nov 2017 10:35:47 +0800
From:   Yunlong Song <yunlong.song@...wei.com>
To:     Jaegeuk Kim <jaegeuk@...nel.org>
CC:     <chao@...nel.org>, <yuchao0@...wei.com>, <yunlong.song@...oud.com>,
        <miaoxie@...wei.com>, <bintian.wang@...wei.com>,
        <linux-fsdevel@...r.kernel.org>,
        <linux-f2fs-devel@...ts.sourceforge.net>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] f2fs: fix out-of-free problem caused by atomic write

This patch tries its best to collect prefree segments and make it free 
to be used
in the commit process, or it will use up free segments since prefree 
segments
can not be used during commit process.

As for your suggestion, I do consider that in an initial patch which 
does not send
out, but I am afraid that will lead to long latency if the atomic file 
is large and the
device is almost full and fragmented.

On 2017/11/7 9:55, Jaegeuk Kim wrote:
> On 11/06, Yunlong Song wrote:
>> f2fs_balance_fs only actives once in the commit_inmem_pages, but there
>> are more than one page to commit, so all the other pages will miss the
>> check. This will lead to out-of-free problem when commit a very large
>> file. However, we cannot do f2fs_balance_fs for each inmem page, since
>> this will break atomicity. As a result, we should collect prefree
>> segments if needed.
>>
>> Signed-off-by: Yunlong Song <yunlong.song@...wei.com>
>> ---
>>   fs/f2fs/f2fs.h    |  1 +
>>   fs/f2fs/segment.c | 24 +++++++++++++++++++++++-
>>   2 files changed, 24 insertions(+), 1 deletion(-)
>>
>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>> index 13a96b8..04ce48f 100644
>> --- a/fs/f2fs/f2fs.h
>> +++ b/fs/f2fs/f2fs.h
>> @@ -610,6 +610,7 @@ struct f2fs_inode_info {
>>   	struct list_head inmem_pages;	/* inmemory pages managed by f2fs */
>>   	struct task_struct *inmem_task;	/* store inmemory task */
>>   	struct mutex inmem_lock;	/* lock for inmemory pages */
>> +	unsigned long inmem_blocks;	/* inmemory blocks */
>>   	struct extent_tree *extent_tree;	/* cached extent_tree entry */
>>   	struct rw_semaphore dio_rwsem[2];/* avoid racing between dio and gc */
>>   	struct rw_semaphore i_mmap_sem;
>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>> index 46dfbca..b87ede4 100644
>> --- a/fs/f2fs/segment.c
>> +++ b/fs/f2fs/segment.c
>> @@ -210,6 +210,7 @@ void register_inmem_page(struct inode *inode, struct page *page)
>>   		list_add_tail(&fi->inmem_ilist, &sbi->inode_list[ATOMIC_FILE]);
>>   	spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);
>>   	inc_page_count(F2FS_I_SB(inode), F2FS_INMEM_PAGES);
>> +	fi->inmem_blocks++;
>>   	mutex_unlock(&fi->inmem_lock);
>>   
>>   	trace_f2fs_register_inmem_page(page, INMEM);
>> @@ -221,6 +222,7 @@ static int __revoke_inmem_pages(struct inode *inode,
>>   	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
>>   	struct inmem_pages *cur, *tmp;
>>   	int err = 0;
>> +	struct f2fs_inode_info *fi = F2FS_I(inode);
>>   
>>   	list_for_each_entry_safe(cur, tmp, head, list) {
>>   		struct page *page = cur->page;
>> @@ -263,6 +265,7 @@ static int __revoke_inmem_pages(struct inode *inode,
>>   		list_del(&cur->list);
>>   		kmem_cache_free(inmem_entry_slab, cur);
>>   		dec_page_count(F2FS_I_SB(inode), F2FS_INMEM_PAGES);
>> +		fi->inmem_blocks--;
>>   	}
>>   	return err;
>>   }
>> @@ -302,6 +305,10 @@ void drop_inmem_pages(struct inode *inode)
>>   	if (!list_empty(&fi->inmem_ilist))
>>   		list_del_init(&fi->inmem_ilist);
>>   	spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);
>> +	if (fi->inmem_blocks) {
>> +		f2fs_bug_on(sbi, 1);
>> +		fi->inmem_blocks = 0;
>> +	}
>>   	mutex_unlock(&fi->inmem_lock);
>>   
>>   	clear_inode_flag(inode, FI_ATOMIC_FILE);
>> @@ -326,6 +333,7 @@ void drop_inmem_page(struct inode *inode, struct page *page)
>>   
>>   	f2fs_bug_on(sbi, !cur || cur->page != page);
>>   	list_del(&cur->list);
>> +	fi->inmem_blocks--;
>>   	mutex_unlock(&fi->inmem_lock);
>>   
>>   	dec_page_count(sbi, F2FS_INMEM_PAGES);
>> @@ -410,6 +418,16 @@ int commit_inmem_pages(struct inode *inode)
>>   
>>   	INIT_LIST_HEAD(&revoke_list);
>>   	f2fs_balance_fs(sbi, true);
>> +	if (prefree_segments(sbi)
>> +		&& has_not_enough_free_secs(sbi, 0,
>> +		fi->inmem_blocks / BLKS_PER_SEC(sbi))) {
>> +		struct cp_control cpc;
>> +
>> +		cpc.reason = __get_cp_reason(sbi);
>> +		err = write_checkpoint(sbi, &cpc);
>> +		if (err)
>> +			goto drop;
> What do you want to guarantee with this? How about passing target # of segments
> into f2fs_balance_fs() so that f2fs_gc() could secure wanted free space in a
> loop?
>
> Thanks,
>
>> +	}
>>   	f2fs_lock_op(sbi);
>>   
>>   	set_inode_flag(inode, FI_ATOMIC_COMMIT);
>> @@ -429,7 +447,7 @@ int commit_inmem_pages(struct inode *inode)
>>   		ret = __revoke_inmem_pages(inode, &revoke_list, false, true);
>>   		if (ret)
>>   			err = ret;
>> -
>> +drop:
>>   		/* drop all uncommitted pages */
>>   		__revoke_inmem_pages(inode, &fi->inmem_pages, true, false);
>>   	}
>> @@ -437,6 +455,10 @@ int commit_inmem_pages(struct inode *inode)
>>   	if (!list_empty(&fi->inmem_ilist))
>>   		list_del_init(&fi->inmem_ilist);
>>   	spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);
>> +	if (fi->inmem_blocks) {
>> +		f2fs_bug_on(sbi, 1);
>> +		fi->inmem_blocks = 0;
>> +	}
>>   	mutex_unlock(&fi->inmem_lock);
>>   
>>   	clear_inode_flag(inode, FI_ATOMIC_COMMIT);
>> -- 
>> 1.8.5.2
> .
>

-- 
Thanks,
Yunlong Song