[PATCH v10 08/10] erofs: support unencoded inodes for page cache share

[Gao Xiang]

On 2025/12/23 09:56, Hongbo Li wrote:
> This patch adds inode page cache sharing functionality for unencoded
> files.
> 
> I conducted experiments in the container environment. Below is the
> memory usage for reading all files in two different minor versions
> of container images:
> 
> +-------------------+------------------+-------------+---------------+
> |       Image       | Page Cache Share | Memory (MB) |    Memory     |
> |                   |                  |             | Reduction (%) |
> +-------------------+------------------+-------------+---------------+
> |                   |        No        |     241     |       -       |
> |       redis       +------------------+-------------+---------------+
> |   7.2.4 & 7.2.5   |        Yes       |     163     |      33%      |
> +-------------------+------------------+-------------+---------------+
> |                   |        No        |     872     |       -       |
> |      postgres     +------------------+-------------+---------------+
> |    16.1 & 16.2    |        Yes       |     630     |      28%      |
> +-------------------+------------------+-------------+---------------+
> |                   |        No        |     2771    |       -       |
> |     tensorflow    +------------------+-------------+---------------+
> |  2.11.0 & 2.11.1  |        Yes       |     2340    |      16%      |
> +-------------------+------------------+-------------+---------------+
> |                   |        No        |     926     |       -       |
> |       mysql       +------------------+-------------+---------------+
> |  8.0.11 & 8.0.12  |        Yes       |     735     |      21%      |
> +-------------------+------------------+-------------+---------------+
> |                   |        No        |     390     |       -       |
> |       nginx       +------------------+-------------+---------------+
> |   7.2.4 & 7.2.5   |        Yes       |     219     |      44%      |
> +-------------------+------------------+-------------+---------------+
> |       tomcat      |        No        |     924     |       -       |
> | 10.1.25 & 10.1.26 +------------------+-------------+---------------+
> |                   |        Yes       |     474     |      49%      |
> +-------------------+------------------+-------------+---------------+
> 
> Additionally, the table below shows the runtime memory usage of the
> container:
> 
> +-------------------+------------------+-------------+---------------+
> |       Image       | Page Cache Share | Memory (MB) |    Memory     |
> |                   |                  |             | Reduction (%) |
> +-------------------+------------------+-------------+---------------+
> |                   |        No        |      35     |       -       |
> |       redis       +------------------+-------------+---------------+
> |   7.2.4 & 7.2.5   |        Yes       |      28     |      20%      |
> +-------------------+------------------+-------------+---------------+
> |                   |        No        |     149     |       -       |
> |      postgres     +------------------+-------------+---------------+
> |    16.1 & 16.2    |        Yes       |      95     |      37%      |
> +-------------------+------------------+-------------+---------------+
> |                   |        No        |     1028    |       -       |
> |     tensorflow    +------------------+-------------+---------------+
> |  2.11.0 & 2.11.1  |        Yes       |     930     |      10%      |
> +-------------------+------------------+-------------+---------------+
> |                   |        No        |     155     |       -       |
> |       mysql       +------------------+-------------+---------------+
> |  8.0.11 & 8.0.12  |        Yes       |     132     |      15%      |
> +-------------------+------------------+-------------+---------------+
> |                   |        No        |      25     |       -       |
> |       nginx       +------------------+-------------+---------------+
> |   7.2.4 & 7.2.5   |        Yes       |      20     |      20%      |
> +-------------------+------------------+-------------+---------------+
> |       tomcat      |        No        |     186     |       -       |
> | 10.1.25 & 10.1.26 +------------------+-------------+---------------+
> |                   |        Yes       |      98     |      48%      |
> +-------------------+------------------+-------------+---------------+
> 
> Co-developed-by: Hongzhen Luo <hongzhen at linux.alibaba.com>
> Signed-off-by: Hongzhen Luo <hongzhen at linux.alibaba.com>
> Signed-off-by: Hongbo Li <lihongbo22 at huawei.com>
> ---

...

> index 4b46016bcd03..269b53b3ed79 100644
> --- a/fs/erofs/ishare.c
> +++ b/fs/erofs/ishare.c
> @@ -197,6 +197,37 @@ const struct file_operations erofs_ishare_fops = {
>   	.splice_read	= filemap_splice_read,
>   };
>   
> +/*
> + * erofs_ishare_iget - find the backing inode.
> + */
> +struct inode *erofs_ishare_iget(struct inode *inode)

Just:

struct inode *erofs_get_real_inode(struct inode *inode)

`ishare_` prefix seems useless here.

> +{
> +	struct erofs_inode *vi, *vi_dedup;
> +	struct inode *realinode;
> +
> +	if (!erofs_is_ishare_inode(inode))
> +		return igrab(inode);
> +
> +	vi_dedup = EROFS_I(inode);
> +	spin_lock(&vi_dedup->lock);
> +	/* fall back to all backing inodes */
> +	DBG_BUGON(list_empty(&vi_dedup->backing_head));
> +	list_for_each_entry(vi, &vi_dedup->backing_head, backing_link) {
> +		realinode = igrab(&vi->vfs_inode);
> +		if (realinode)
> +			break;
> +	}
> +	spin_unlock(&vi_dedup->lock);
> +
> +	DBG_BUGON(!realinode);
> +	return realinode;
> +}
> +
> +void erofs_ishare_iput(struct inode *realinode)

Just:

erofs_put_real_inode().

Thanks,
Gao Xiang