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

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Date:   Fri, 3 Jun 2022 17:11:10 +0200
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     Hsin-Yi Wang <hsinyi@...omium.org>
Cc:     Matthew Wilcox <willy@...radead.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,

On 03.06.2022 16:55, Hsin-Yi Wang wrote:
> On Fri, Jun 3, 2022 at 10:10 PM Marek Szyprowski
> <m.szyprowski@...sung.com> wrote:
>> 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.
>>
> Hi Marek,
>
> Are there any obvious squashfs errors in dmesg? Did you enable
> CONFIG_SQUASHFS_FILE_DIRECT or CONFIG_SQUASHFS_FILE_CACHE?

Here are related config entries from my .config:

CONFIG_SQUASHFS=y
CONFIG_SQUASHFS_FILE_CACHE=y
# CONFIG_SQUASHFS_FILE_DIRECT is not set
CONFIG_SQUASHFS_DECOMP_SINGLE=y
# CONFIG_SQUASHFS_DECOMP_MULTI is not set
# CONFIG_SQUASHFS_DECOMP_MULTI_PERCPU is not set
# CONFIG_SQUASHFS_XATTR is not set
CONFIG_SQUASHFS_ZLIB=y
# CONFIG_SQUASHFS_LZ4 is not set
CONFIG_SQUASHFS_LZO=y
CONFIG_SQUASHFS_XZ=y
# CONFIG_SQUASHFS_ZSTD is not set
# CONFIG_SQUASHFS_4K_DEVBLK_SIZE is not set
# CONFIG_SQUASHFS_EMBEDDED is not set
CONFIG_SQUASHFS_FRAGMENT_CACHE_SIZE=3

(I've used standard ARM 32bit multi_v7_defconfig)

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