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Date: Tue, 7 Nov 2017 11:10:07 +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
I test it in an old kernel and find it hangs in gc process, maybe it is
a bug of
old kernel.
On 2017/11/7 10:49, Jaegeuk Kim wrote:
> On 11/07, Yunlong Song wrote:
>> 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.
> Why? f2fs_balance_fs() would be fine to return, if target # of segments can
> be found from prefree_segments() by checkpoint like what you did. Otherwise,
> it needs to call f2fs_gc().
>
>> 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
>>
> .
>
--
Thanks,
Yunlong Song
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