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Subject: Re: [PATCH v11 0/4] scsi: ufs: Add Host Performance Booster Support
Reply-To: daejun7.park@samsung.com
From:   Daejun Park <daejun7.park@samsung.com>
To:     Christoph Hellwig <hch@infradead.org>,
        Daejun Park <daejun7.park@samsung.com>
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> > Hi All,
> > 
> > I want to know how to improve this patch.
> 
> Drop it and fix the actual UFS feature to not be so horrible?
> 

Hello Christoph,

Thanks for the comment.

The HPB is essential feature for mobile devices.

NAND-based storage needs logical to physical mapping, which is cached in
the storage to minimize translation overhead. UFS is a NAND-based storage
device with limited resources, mainly used for mobile devices. Typically,
SSD has enough cache space for mapping information in SSD, but UFS has not
enough.
So, UFS stores L2P mapping in NAND and performs IO using demand loading 
for translation. Due to overhead of demand loading, it degrades random read
performance.

The HPB is a feature which uses host memory to relieve this problem. By 
using the HPB feature, UFS can provide improved random read performance
without mapping data thrashing problem. Therefore, the HPB is currently
already included in the Linux kernel code in android devices, however it 
is maintained as out-of-tree.

While upstreaming HPB feature to mainline kernel, we received various
comments from several reviewers (thanks!) and the HPB feature can be
improved. I think it would be good to make mainline the feature that are
mainly used.

Thanks,
Daejun