linux-kernel - Re: [PATCH] f2fs: avoid false positive of free secs check

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Date:   Thu, 30 Nov 2017 15:15:11 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     Yunlong Song <yunlong.song@...wei.com>, Chao Yu <chao@...nel.org>,
        <jaegeuk@...nel.org>, <yunlong.song@...oud.com>
CC:     <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] f2fs: avoid false positive of free secs check

On 2017/11/30 10:42, Yunlong Song wrote:
> SSR can make hot/warm/cold nodes written together, so why should we account
> them different?

Current segment which is using ssr allocation has only one valid type, so we
can not write data/node with different type into current segment which already
has fixed type, right?

Thanks,

> 
> On 2017/11/29 19:56, Chao Yu wrote:
>> On 2017/11/27 14:54, Yunlong Song wrote:
>>> Sometimes f2fs_gc is called with no target victim (e.g. xfstest
>>> generic/027, ndirty_node:545 ndiry_dent:1 ndirty_imeta:513 rsvd_segs:21
>>> free_segs:27, has_not_enough_free_secs will return true). This patch
>>> first merges pages and then converts into sections.
>> I don't think this could be right, IMO, instead, it would be better to
>> account dirty hot/warm/cold nodes or imeta separately, as actually, they
>> will use different section, but currently, our calculation way is based
>> on that they could be written to same section.
>>
>> Thanks,
>>
>>> Signed-off-by: Yunlong Song <yunlong.song@...wei.com>
>>> ---
>>>   fs/f2fs/f2fs.h    |  9 ---------
>>>   fs/f2fs/segment.c | 12 +++++++-----
>>>   fs/f2fs/segment.h | 13 +++++++++----
>>>   3 files changed, 16 insertions(+), 18 deletions(-)
>>>
>>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>>> index ca6b0c9..e89cff7 100644
>>> --- a/fs/f2fs/f2fs.h
>>> +++ b/fs/f2fs/f2fs.h
>>> @@ -1675,15 +1675,6 @@ static inline int get_dirty_pages(struct inode *inode)
>>>   	return atomic_read(&F2FS_I(inode)->dirty_pages);
>>>   }
>>>   
>>> -static inline int get_blocktype_secs(struct f2fs_sb_info *sbi, int block_type)
>>> -{
>>> -	unsigned int pages_per_sec = sbi->segs_per_sec * sbi->blocks_per_seg;
>>> -	unsigned int segs = (get_pages(sbi, block_type) + pages_per_sec - 1) >>
>>> -						sbi->log_blocks_per_seg;
>>> -
>>> -	return segs / sbi->segs_per_sec;
>>> -}
>>> -
>>>   static inline block_t valid_user_blocks(struct f2fs_sb_info *sbi)
>>>   {
>>>   	return sbi->total_valid_block_count;
>>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>>> index c117e09..603f805 100644
>>> --- a/fs/f2fs/segment.c
>>> +++ b/fs/f2fs/segment.c
>>> @@ -171,17 +171,19 @@ static unsigned long __find_rev_next_zero_bit(const unsigned long *addr,
>>>   
>>>   bool need_SSR(struct f2fs_sb_info *sbi)
>>>   {
>>> -	int node_secs = get_blocktype_secs(sbi, F2FS_DIRTY_NODES);
>>> -	int dent_secs = get_blocktype_secs(sbi, F2FS_DIRTY_DENTS);
>>> -	int imeta_secs = get_blocktype_secs(sbi, F2FS_DIRTY_IMETA);
>>> +	s64 node_pages = get_pages(sbi, F2FS_DIRTY_NODES);
>>> +	s64 dent_pages = get_pages(sbi, F2FS_DIRTY_DENTS);
>>> +	s64 imeta_pages = get_pages(sbi, F2FS_DIRTY_IMETA);
>>>   
>>>   	if (test_opt(sbi, LFS))
>>>   		return false;
>>>   	if (sbi->gc_thread && sbi->gc_thread->gc_urgent)
>>>   		return true;
>>>   
>>> -	return free_sections(sbi) <= (node_secs + 2 * dent_secs + imeta_secs +
>>> -			SM_I(sbi)->min_ssr_sections + reserved_sections(sbi));
>>> +	return free_sections(sbi) <=
>>> +		(PAGE2SEC(sbi, node_pages + imeta_pages) +
>>> +		PAGE2SEC(sbi, 2 * dent_pages) +
>>> +		SM_I(sbi)->min_ssr_sections + reserved_sections(sbi));
>>>   }
>>>   
>>>   void register_inmem_page(struct inode *inode, struct page *page)
>>> diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
>>> index d1d394c..723d79e 100644
>>> --- a/fs/f2fs/segment.h
>>> +++ b/fs/f2fs/segment.h
>>> @@ -115,6 +115,10 @@
>>>   #define SECTOR_TO_BLOCK(sectors)					\
>>>   	((sectors) >> F2FS_LOG_SECTORS_PER_BLOCK)
>>>   
>>> +#define PAGE2SEC(sbi, pages)				\
>>> +	((((pages) + BLKS_PER_SEC(sbi) - 1)		\
>>> +	>> sbi->log_blocks_per_seg) / sbi->segs_per_sec)
>>> +
>>>   /*
>>>    * indicate a block allocation direction: RIGHT and LEFT.
>>>    * RIGHT means allocating new sections towards the end of volume.
>>> @@ -527,9 +531,9 @@ static inline bool has_curseg_enough_space(struct f2fs_sb_info *sbi)
>>>   static inline bool has_not_enough_free_secs(struct f2fs_sb_info *sbi,
>>>   					int freed, int needed)
>>>   {
>>> -	int node_secs = get_blocktype_secs(sbi, F2FS_DIRTY_NODES);
>>> -	int dent_secs = get_blocktype_secs(sbi, F2FS_DIRTY_DENTS);
>>> -	int imeta_secs = get_blocktype_secs(sbi, F2FS_DIRTY_IMETA);
>>> +	s64 node_pages = get_pages(sbi, F2FS_DIRTY_NODES);
>>> +	s64 dent_pages = get_pages(sbi, F2FS_DIRTY_DENTS);
>>> +	s64 imeta_pages = get_pages(sbi, F2FS_DIRTY_IMETA);
>>>   
>>>   	if (unlikely(is_sbi_flag_set(sbi, SBI_POR_DOING)))
>>>   		return false;
>>> @@ -538,7 +542,8 @@ static inline bool has_not_enough_free_secs(struct f2fs_sb_info *sbi,
>>>   			has_curseg_enough_space(sbi))
>>>   		return false;
>>>   	return (free_sections(sbi) + freed) <=
>>> -		(node_secs + 2 * dent_secs + imeta_secs +
>>> +		(PAGE2SEC(sbi, node_pages + imeta_pages) +
>>> +		PAGE2SEC(sbi, 2 * dent_pages) +
>>>   		reserved_sections(sbi) + needed);
>>>   }
>>>   
>>>
>> .
>>
>