linux-kernel - Re: [PATCH 2/3] f2fs: fix get stale meta pages when build free nids

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Date:	Mon, 9 Mar 2015 12:24:53 +0800
From:	Wanpeng Li <wanpeng.li@...ux.intel.com>
To:	Jaegeuk Kim <jaegeuk@...nel.org>
Cc:	Changman Lee <cm224.lee@...sung.com>,
	Chao Yu <chao2.yu@...sung.com>,
	linux-f2fs-devel@...ts.sourceforge.net,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	Wanpeng Li <wanpeng.li@...ux.intel.com>
Subject: Re: [PATCH 2/3] f2fs: fix get stale meta pages when build free nids

Hi Jaegeuk,
On Sun, Mar 08, 2015 at 09:18:47PM -0700, Jaegeuk Kim wrote:
>Hi Wanpeng,
>
>On Mon, Mar 09, 2015 at 11:00:54AM +0800, Wanpeng Li wrote:
>> The blocks of nat pages to be scanned will be readahead when build free 
>> nids. The start blkno will be adjusted to 0 when the intended range over 
>> max_nids, then function ra_meta_pages readahead the right blkno, however, 
>> function get_current_nat_page which is called in build_free_nids still 
>> get the meta pages w/ stale blkno, this patch fix it by adjusting the nid 
>> and the blkno which will be readahead in avdance in order to readahead and 
>> get the right meta pages.
>> 
>> Signed-off-by: Wanpeng Li <wanpeng.li@...ux.intel.com>
>> ---
>>  fs/f2fs/checkpoint.c | 3 ---
>>  fs/f2fs/node.c       | 9 ++++++++-
>>  2 files changed, 8 insertions(+), 4 deletions(-)
>> 
>> diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
>> index 53bc328..aedb441 100644
>> --- a/fs/f2fs/checkpoint.c
>> +++ b/fs/f2fs/checkpoint.c
>> @@ -129,9 +129,6 @@ int ra_meta_pages(struct f2fs_sb_info *sbi, block_t start, int nrpages, int type
>>  
>>  		switch (type) {
>>  		case META_NAT:
>> -			if (unlikely(blkno >=
>> -					NAT_BLOCK_OFFSET(NM_I(sbi)->max_nid)))
>> -				blkno = 0;
>>  			/* get nat block addr */
>>  			fio.blk_addr = current_nat_addr(sbi,
>>  					blkno * NAT_ENTRY_PER_BLOCK);
>> diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
>> index 1a7e925..8751375 100644
>> --- a/fs/f2fs/node.c
>> +++ b/fs/f2fs/node.c
>> @@ -1509,13 +1509,20 @@ static void build_free_nids(struct f2fs_sb_info *sbi)
>>  	struct f2fs_summary_block *sum = curseg->sum_blk;
>>  	int i = 0;
>>  	nid_t nid = nm_i->next_scan_nid;
>> +	block_t blkno = NAT_BLOCK_OFFSET(nid);
>>  
>>  	/* Enough entries */
>>  	if (nm_i->fcnt > NAT_ENTRY_PER_BLOCK)
>>  		return;
>>  
>> +	if (unlikely(blkno >=
>> +			NAT_BLOCK_OFFSET(NM_I(sbi)->max_nid))) {
>> +		blkno = 0;
>> +		nid = 0;
>> +	}
>
>The assumption here is that the nid does not exceeed max_nid, since the
>previous call already set next_scan_nid to 0, if it exceeds max_nid.
>So, we don't need to do like this.

So get_current_nat_page in while(1) still get the wrong meta page for
one time, right? The nid will be set to 0 in the second round.

Regards,
Wanpeng Li 

>
>BTW, even if ra_meta_pages doesn't get the below condition,
>		if (unlikely(blkno >=
>				NAT_BLOCK_OFFSET(NM_I(sbi)->max_nid)))
>			blkno = 0;
>IMO, it is still worth to remain that to avoid any bugs due to further code
>changes. It makes sense that unlikely was used for this too.
>
>Thanks,
>
>> +
>>  	/* readahead nat pages to be scanned */
>> -	ra_meta_pages(sbi, NAT_BLOCK_OFFSET(nid), FREE_NID_PAGES, META_NAT);
>> +	ra_meta_pages(sbi, blkno, FREE_NID_PAGES, META_NAT);
>>  
>>  	while (1) {
>>  		struct page *page = get_current_nat_page(sbi, nid);
>> -- 
>> 1.9.1
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