linux-kernel - Re: [f2fs-dev] [RFC v3] f2fs: extent cache: support unaligned extent

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Date:   Thu, 5 Aug 2021 21:35:46 +0800
From:   Chao Yu <chao@...nel.org>
To:     Jaegeuk Kim <jaegeuk@...nel.org>
Cc:     Chao Yu <chao.yu@...ux.dev>, linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [f2fs-dev] [RFC v3] f2fs: extent cache: support unaligned extent

On 2021/8/5 7:45, Jaegeuk Kim wrote:
> Chao,
> 
> How about this?
> https://github.com/jaegeuk/f2fs/commit/d6bbe121bc24dfabfedc07ba7cb6e921fb70ece0
> 
> I'm digging one bug in __insert_extent_tree w/ the patch tho.
> 
> On 08/04, Jaegeuk Kim wrote:
>> On 08/04, Chao Yu wrote:
>>> Compressed inode may suffer read performance issue due to it can not
>>> use extent cache, so I propose to add this unaligned extent support
>>> to improve it.
>>>
>>> Currently, it only works in readonly format f2fs image.
>>>
>>> Unaligned extent: in one compressed cluster, physical block number
>>> will be less than logical block number, so we add an extra physical
>>> block length in extent info in order to indicate such extent status.
>>>
>>> The idea is if one whole cluster blocks are contiguous physically,
>>> once its mapping info was readed at first time, we will cache an
>>> unaligned (or aligned) extent info entry in extent cache, it expects
>>> that the mapping info will be hitted when rereading cluster.
>>>
>>> Merge policy:
>>> - Aligned extents can be merged.
>>> - Aligned extent and unaligned extent can not be merged.
>>>
>>> Signed-off-by: Chao Yu <chao@...nel.org>
>>> ---
>>> v3:
>>> - avoid CONFIG_F2FS_FS_COMPRESSION as much as possible
>>> - clean up codes
>>>   fs/f2fs/compress.c     | 24 ++++++++++++
>>>   fs/f2fs/data.c         | 28 +++++++++++---
>>>   fs/f2fs/extent_cache.c | 88 +++++++++++++++++++++++++++++++++++++-----
>>>   fs/f2fs/f2fs.h         | 42 +++++++++++++++++---
>>>   fs/f2fs/node.c         | 18 +++++++++
>>>   5 files changed, 179 insertions(+), 21 deletions(-)
>>>
>>> diff --git a/fs/f2fs/compress.c b/fs/f2fs/compress.c
>>> index 4aa166d3d9bf..296ff37d4b08 100644
>>> --- a/fs/f2fs/compress.c
>>> +++ b/fs/f2fs/compress.c
>>> @@ -1719,6 +1719,30 @@ void f2fs_put_page_dic(struct page *page)
>>>   	f2fs_put_dic(dic);
>>>   }
>>>   
>>> +/*
>>> + * check whether cluster blocks are contiguous, and add extent cache entry
>>> + * only if cluster blocks are logically and physically contiguous.
>>> + */
>>> +int f2fs_cluster_blocks_are_contiguous(struct dnode_of_data *dn)
>>> +{
>>> +	bool compressed = f2fs_data_blkaddr(dn) == COMPRESS_ADDR;
>>> +	int i = compressed ? 1 : 0;
>>> +	block_t first_blkaddr = data_blkaddr(dn->inode, dn->node_page,
>>> +						dn->ofs_in_node + i);
>>> +
>>> +	for (i += 1; i < F2FS_I(dn->inode)->i_cluster_size; i++) {
>>> +		block_t blkaddr = data_blkaddr(dn->inode, dn->node_page,
>>> +						dn->ofs_in_node + i);
>>> +
>>> +		if (!__is_valid_data_blkaddr(blkaddr))
>>> +			break;
>>> +		if (first_blkaddr + i - 1 != blkaddr)
>>> +			return 0;

The merge condition looks wrong, shouldn't be:

if (first_blkaddr + i - compressed ? 1 : 0 != blkaddr)
	return 0;

Thanks,