linux-kernel - Re: [f2fs-dev] [PATCH v3] f2fs: don't use GFP

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Message-ID: <9a8252b5-4f41-9a9f-d6c6-06355af83e4b@huawei.com>
Date:   Tue, 10 Apr 2018 15:27:25 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     Jaegeuk Kim <jaegeuk@...nel.org>
CC:     <linux-kernel@...r.kernel.org>,
        <linux-f2fs-devel@...ts.sourceforge.net>
Subject: Re: [f2fs-dev] [PATCH v3] f2fs: don't use GFP_ZERO for page caches

On 2018/4/10 14:40, Jaegeuk Kim wrote:
> On 04/10, Chao Yu wrote:
>> On 2018/4/10 11:29, Jaegeuk Kim wrote:
>>> Change log from v2:
>>>  - consider IO error case when dealing with metapage
>>>  - memset by fill_node_footer
>>>
>>> Change log from v1:
>>>  - don't memset for recovered page
>>>  
>>> Related to https://lkml.org/lkml/2018/4/8/661
>>>
>>> Sometimes, we need to write meta data to new allocated block address,
>>> then we will allocate a zeroed page in inner inode's address space, and
>>> fill partial data in it, and leave other place with zero value which means
>>> some fields are initial status.
>>>
>>> There are two inner inodes (meta inode and node inode) setting __GFP_ZERO,
>>> I have just checked them, for both of them, we can avoid using __GFP_ZERO,
>>> and do initialization by ourselves to avoid unneeded/redundant zeroing
>>> from mm.
>>>
>>> Cc: <stable@...r.kernel.org>
>>> Signed-off-by: Chao Yu <yuchao0@...wei.com>
>>> Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
>>> ---
>>>  fs/f2fs/checkpoint.c | 4 +++-
>>>  fs/f2fs/inode.c      | 4 ++--
>>>  fs/f2fs/segment.c    | 3 +++
>>>  fs/f2fs/segment.h    | 1 +
>>>  4 files changed, 9 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
>>> index bf779461df13..2e23b953d304 100644
>>> --- a/fs/f2fs/checkpoint.c
>>> +++ b/fs/f2fs/checkpoint.c
>>> @@ -100,8 +100,10 @@ static struct page *__get_meta_page(struct f2fs_sb_info *sbi, pgoff_t index,
>>>  	 * readonly and make sure do not write checkpoint with non-uptodate
>>>  	 * meta page.
>>>  	 */
>>> -	if (unlikely(!PageUptodate(page)))
>>> +	if (unlikely(!PageUptodate(page))) {
>>> +		memset(page_address(page), 0, PAGE_SIZE);
>>>  		f2fs_stop_checkpoint(sbi, false);
>>> +	}
>>>  out:
>>>  	return page;
>>>  }
>>> diff --git a/fs/f2fs/inode.c b/fs/f2fs/inode.c
>>> index 417c9dcd0269..87535bf63421 100644
>>> --- a/fs/f2fs/inode.c
>>> +++ b/fs/f2fs/inode.c
>>> @@ -320,10 +320,10 @@ struct inode *f2fs_iget(struct super_block *sb, unsigned long ino)
>>>  make_now:
>>>  	if (ino == F2FS_NODE_INO(sbi)) {
>>>  		inode->i_mapping->a_ops = &f2fs_node_aops;
>>> -		mapping_set_gfp_mask(inode->i_mapping, GFP_F2FS_ZERO);
>>> +		mapping_set_gfp_mask(inode->i_mapping, GFP_NOFS);
>>>  	} else if (ino == F2FS_META_INO(sbi)) {
>>>  		inode->i_mapping->a_ops = &f2fs_meta_aops;
>>> -		mapping_set_gfp_mask(inode->i_mapping, GFP_F2FS_ZERO);
>>> +		mapping_set_gfp_mask(inode->i_mapping, GFP_NOFS);
>>>  	} else if (S_ISREG(inode->i_mode)) {
>>>  		inode->i_op = &f2fs_file_inode_operations;
>>>  		inode->i_fop = &f2fs_file_operations;
>>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>>> index a4b8e3e24ccb..1f5db557ab96 100644
>>> --- a/fs/f2fs/segment.c
>>> +++ b/fs/f2fs/segment.c
>>> @@ -2021,6 +2021,7 @@ static void write_current_sum_page(struct f2fs_sb_info *sbi,
>>>  	struct f2fs_summary_block *dst;
>>>  
>>>  	dst = (struct f2fs_summary_block *)page_address(page);
>>> +	memset(dst, 0, PAGE_SIZE);
>>
>> We will fill all summary page later, so we don't need initialize it?
> 
> I'd like to reserve the uninitialzed space as zeros for future reference.

No problem, anyway, the patch is OK to me. :)

Thanks,

> 
>>
>>>  
>>>  	mutex_lock(&curseg->curseg_mutex);
>>>  
>>> @@ -3117,6 +3118,7 @@ static void write_compacted_summaries(struct f2fs_sb_info *sbi, block_t blkaddr)
>>>  
>>>  	page = grab_meta_page(sbi, blkaddr++);
>>>  	kaddr = (unsigned char *)page_address(page);
>>> +	memset(kaddr, 0, PAGE_SIZE);
>>
>> I checked here, we will not use uninitialized space due to:
>>
>> read_compacted_summaries()
>> {
>> ...
>> 	if (offset + SUMMARY_SIZE <= PAGE_SIZE - SUM_FOOTER_SIZE)
>> 		continue;
>> ...
>> }
>>
>> Are we safe here?
>>
>>>  
>>>  	/* Step 1: write nat cache */
>>>  	seg_i = CURSEG_I(sbi, CURSEG_HOT_DATA);
>>> @@ -3141,6 +3143,7 @@ static void write_compacted_summaries(struct f2fs_sb_info *sbi, block_t blkaddr)
>>>  			if (!page) {
>>>  				page = grab_meta_page(sbi, blkaddr++);
>>>  				kaddr = (unsigned char *)page_address(page);
>>> +				memset(kaddr, 0, PAGE_SIZE);
>>
>> Ditto.
>>
>>>  				written_size = 0;
>>>  			}
>>>  			summary = (struct f2fs_summary *)(kaddr + written_size);
>>> diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
>>> index 3325d0769723..492ad0c86fa9 100644
>>> --- a/fs/f2fs/segment.h
>>> +++ b/fs/f2fs/segment.h
>>> @@ -375,6 +375,7 @@ static inline void seg_info_to_sit_page(struct f2fs_sb_info *sbi,
>>>  	int i;
>>>  
>>>  	raw_sit = (struct f2fs_sit_block *)page_address(page);
>>> +	memset(raw_sit, 0, PAGE_SIZE);
>>
>> I suspect that root cause of panic is that we don't memset here?
>>
>> Thanks,
>>
>>>  	for (i = 0; i < end - start; i++) {
>>>  		rs = &raw_sit->entries[i];
>>>  		se = get_seg_entry(sbi, start + i);
>>>
> 
> .
>