[PATCH] erofs: fix small compressed files inlining

[Chao Yu]

On 2022/2/4 3:02, Gao Xiang wrote:
> From: Gao Xiang <hsiangkao at linux.alibaba.com>
> 
> Prior to ztailpacking feature, it's enough that each lcluster has
> two pclusters at most, and the last pcluster should be turned into
> an uncompressed pcluster if necessary. For example,
>    _________________________________________________
>   |_ pcluster n-2 _|_ pcluster n-1 _|____ EOFed ____|
> 
> which should be converted into:
>    _________________________________________________
>   |_ pcluster n-2 _|_ pcluster n-1 (uncompressed)' _|
> 
> That is fine since either pcluster n-1 or (uncompressed)' takes one
> physical block.
> 
> However, after ztailpacking supported, the game is changed since the
> last pcluster can be inlined now. And such case above is quite common
> for inlining small files. Therefore, in order to inline such files
> more effectively, special EOF lclusters are now supported which can
> have three parts at most, as illustrated below:
>    _________________________________________________
>   |_ pcluster n-2 _|_ pcluster n-1 _|____ EOFed ____|
>                                     ^ i_size
> 
> Actually similar code exists in Yue Hu's original patchset [1], but I
> removed this part on purpose. After evaluating more real cases with
> small files, I've changed my mind.
> 
> [1] https://lore.kernel.org/r/20211215094449.15162-1-huyue2@yulong.com
> Fixes: ab92184ff8f1 ("erofs: add on-disk compressed tail-packing inline support")
> Signed-off-by: Gao Xiang <hsiangkao at linux.alibaba.com>

Reviewed-by: Chao Yu <chao at kernel.org>

Thanks,