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Date:   Fri, 18 Mar 2022 13:41:59 +0800
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Subject: Re: [PATCH v5 21/22] erofs: implement fscache-based data readahead
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To:     dhowells@redhat.com, linux-cachefs@redhat.com, xiang@kernel.org,
        chao@kernel.org, linux-erofs@lists.ozlabs.org,
        torvalds@linux-foundation.org, gregkh@linuxfoundation.org,
        willy@infradead.org, linux-fsdevel@vger.kernel.org,
        joseph.qi@linux.alibaba.com, bo.liu@linux.alibaba.com,
        tao.peng@linux.alibaba.com, gerry@linux.alibaba.com,
        eguan@linux.alibaba.com, linux-kernel@vger.kernel.org,
        luodaowen.backend@bytedance.com
References: <20220316131723.111553-1-jefflexu@linux.alibaba.com>
 <20220316131723.111553-22-jefflexu@linux.alibaba.com>
 <YjLFsCLeEU9glmNf@B-P7TQMD6M-0146.local>
From:   JeffleXu <jefflexu@linux.alibaba.com>
In-Reply-To: <YjLFsCLeEU9glmNf@B-P7TQMD6M-0146.local>
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On 3/17/22 1:22 PM, Gao Xiang wrote:
> On Wed, Mar 16, 2022 at 09:17:22PM +0800, Jeffle Xu wrote:
>> This patch implements fscache-based data readahead. Also registers an
>> individual bdi for each erofs instance to enable readahead.
>>
>> Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com>
>> ---
>>  fs/erofs/fscache.c | 153 +++++++++++++++++++++++++++++++++++++++++++++
>>  fs/erofs/super.c   |   4 ++
>>  2 files changed, 157 insertions(+)
>>
>> diff --git a/fs/erofs/fscache.c b/fs/erofs/fscache.c
>> index 82c52b6e077e..913ca891deb9 100644
>> --- a/fs/erofs/fscache.c
>> +++ b/fs/erofs/fscache.c
>> @@ -10,6 +10,13 @@ struct erofs_fscache_map {
>>  	u64 m_llen;
>>  };
>>  
>> +struct erofs_fscahce_ra_ctx {
> 
> typo,  should be `erofs_fscache_ra_ctx'

Oops. Thanks.


> 
>> +	struct readahead_control *rac;
>> +	struct address_space *mapping;
>> +	loff_t start;
>> +	size_t len, done;
>> +};
>> +
>>  static struct fscache_volume *volume;
>>  
>>  /*
>> @@ -199,12 +206,158 @@ static int erofs_fscache_readpage(struct file *file, struct page *page)
>>  	return ret;
>>  }
>>  
>> +static inline size_t erofs_fscache_calc_len(struct erofs_fscahce_ra_ctx *ractx,
>> +					    struct erofs_fscache_map *fsmap)
>> +{
>> +	/*
>> +	 * 1) For CHUNK_BASED layout, the output m_la is rounded down to the
>> +	 * nearest chunk boundary, and the output m_llen actually starts from
>> +	 * the start of the containing chunk.
>> +	 * 2) For other cases, the output m_la is equal to o_la.
>> +	 */
>> +	size_t len = fsmap->m_llen - (fsmap->o_la - fsmap->m_la);
>> +
>> +	return min_t(size_t, len, ractx->len - ractx->done);
>> +}
>> +
>> +static inline void erofs_fscache_unlock_pages(struct readahead_control *rac,
>> +					      size_t len)
> 
> Can we convert them into folios in advance? it seems much
> straight-forward to convert these...
> 
> Or I have to convert them later, and it seems unnecessary...

OK I will try to use folio API in the next version.


> 
> 
>> +{
>> +	while (len) {
>> +		struct page *page = readahead_page(rac);
>> +
>> +		SetPageUptodate(page);
>> +		unlock_page(page);
>> +		put_page(page);
>> +
>> +		len -= PAGE_SIZE;
>> +	}
>> +}
>> +
>> +static int erofs_fscache_ra_hole(struct erofs_fscahce_ra_ctx *ractx,
>> +				 struct erofs_fscache_map *fsmap)
>> +{
>> +	struct iov_iter iter;
>> +	loff_t start = ractx->start + ractx->done;
>> +	size_t length = erofs_fscache_calc_len(ractx, fsmap);
>> +
>> +	iov_iter_xarray(&iter, READ, &ractx->mapping->i_pages, start, length);
>> +	iov_iter_zero(length, &iter);
>> +
>> +	erofs_fscache_unlock_pages(ractx->rac, length);
>> +	return length;
>> +}
>> +
>> +static int erofs_fscache_ra_noinline(struct erofs_fscahce_ra_ctx *ractx,
>> +				     struct erofs_fscache_map *fsmap)
>> +{
>> +	struct fscache_cookie *cookie = fsmap->m_ctx->cookie;
>> +	loff_t start = ractx->start + ractx->done;
>> +	size_t length = erofs_fscache_calc_len(ractx, fsmap);
>> +	loff_t pstart = fsmap->m_pa + (fsmap->o_la - fsmap->m_la);
>> +	int ret;
>> +
>> +	ret = erofs_fscache_read_pages(cookie, ractx->mapping,
>> +				       start, length, pstart);
>> +	if (!ret) {
>> +		erofs_fscache_unlock_pages(ractx->rac, length);
>> +		ret = length;
>> +	}
>> +
>> +	return ret;
>> +}
>> +
>> +static int erofs_fscache_ra_inline(struct erofs_fscahce_ra_ctx *ractx,
>> +				   struct erofs_fscache_map *fsmap)
>> +{
> 
> We could fold in this, since it has the only user.

OK, and "struct erofs_fscahce_ra_ctx" is not needed then.

-- 
Thanks,
Jeffle