linux-ext4 - Re: [PATCH v8 4/4] fs: unicode: Add utf8 module and a unicode layer

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Message-ID: <61d85255-d23e-7016-7fb5-7ab0a6b4b39f@collabora.com>
Date:   Tue, 27 Apr 2021 15:39:15 +0530
From:   Shreeya Patel <shreeya.patel@...labora.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     tytso@....edu, adilger.kernel@...ger.ca, jaegeuk@...nel.org,
        chao@...nel.org, krisman@...labora.com, ebiggers@...gle.com,
        drosen@...gle.com, ebiggers@...nel.org, yuchao0@...wei.com,
        linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-fsdevel@...r.kernel.org, kernel@...labora.com,
        andre.almeida@...labora.com
Subject: Re: [PATCH v8 4/4] fs: unicode: Add utf8 module and a unicode layer


On 27/04/21 11:59 am, Christoph Hellwig wrote:
> On Sat, Apr 24, 2021 at 02:21:36AM +0530, Shreeya Patel wrote:
>> utf8data.h_shipped has a large database table which is an auto-generated
>> decodification trie for the unicode normalization functions.
>> We can avoid carrying this large table in the kernel unless it is required
>> by the filesystem during boot process.
>>
>> Hence, make UTF-8 encoding loadable by converting it into a module and
>> also add built-in UTF-8 support option for compiling it into the
>> kernel whenever required by the filesystem.
> The way this is implemement looks rather awkward.
>
> Given that the large memory usage is for a data table and not for code,
> why not treat is as a firmware blob and load it using request_firmware?


utf8 module not just has the data table but also has some kernel code.
The big part that we are trying to keep out of the kernel is a tree 
structure that gets traversed based on a key that is the file name.
This is done when issuing a lookup in the filesystem, which has to be 
very fast. So maybe it would not be so good to use request_firmware for
such a core feature.