linux-kernel - Re: [PATCH v4 3/3] squashfs: implement readahead

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Date:   Fri, 3 Jun 2022 16:10:23 +0200
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Hsin-Yi Wang <hsinyi@...omium.org>,
        Phillip Lougher <phillip@...ashfs.org.uk>,
        Xiongwei Song <Xiongwei.Song@...driver.com>,
        Zheng Liang <zhengliang6@...wei.com>,
        Zhang Yi <yi.zhang@...wei.com>, Hou Tao <houtao1@...wei.com>,
        Miao Xie <miaoxie@...wei.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "linux-mm @ kvack . org" <linux-mm@...ck.org>,
        "squashfs-devel @ lists . sourceforge . net" 
        <squashfs-devel@...ts.sourceforge.net>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 3/3] squashfs: implement readahead

Hi Matthew,

On 03.06.2022 14:59, Matthew Wilcox wrote:
> On Fri, Jun 03, 2022 at 02:54:21PM +0200, Marek Szyprowski wrote:
>> On 01.06.2022 12:39, Hsin-Yi Wang wrote:
>>> Implement readahead callback for squashfs. It will read datablocks
>>> which cover pages in readahead request. For a few cases it will
>>> not mark page as uptodate, including:
>>> - file end is 0.
>>> - zero filled blocks.
>>> - current batch of pages isn't in the same datablock or not enough in a
>>>     datablock.
>>> - decompressor error.
>>> Otherwise pages will be marked as uptodate. The unhandled pages will be
>>> updated by readpage later.
>>>
>>> Suggested-by: Matthew Wilcox <willy@...radead.org>
>>> Signed-off-by: Hsin-Yi Wang <hsinyi@...omium.org>
>>> Reported-by: Matthew Wilcox <willy@...radead.org>
>>> Reported-by: Phillip Lougher <phillip@...ashfs.org.uk>
>>> Reported-by: Xiongwei Song <Xiongwei.Song@...driver.com>
>>> ---
>> This patch landed recently in linux-next as commit 95f7a26191de
>> ("squashfs: implement readahead"). I've noticed that it causes serious
>> issues on my test systems (various ARM 32bit and 64bit based boards).
>> The easiest way to observe is udev timeout 'waiting for /dev to be fully
>> populated' and prolonged booting time. I'm using squashfs for deploying
>> kernel modules via initrd. Reverting aeefca9dfae7 & 95f7a26191deon on
>> top of the next-20220603 fixes the issue.
> How large are these files?  Just a few kilobytes?

Yes, they are small, most of them are smaller than 16KB, some about 
128KB and a few about 256KB. I've sent a detailed list in private mail.

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland