linux-kernel - Re: [PATCH v2] squashfs: Add optional full compressed block caching

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Message-ID: <b6dfcc79-f542-474a-bcc6-4e24a1189a07@squashfs.org.uk>
Date: Wed, 21 May 2025 16:49:30 +0100
From: Phillip Lougher <phillip@...ashfs.org.uk>
To: Chanho Min <chanho.min@....com>, Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-kernel@...r.kernel.org, gunho.lee@....com
Subject: Re: [PATCH v2] squashfs: Add optional full compressed block caching



On 21/05/2025 08:25, Chanho Min wrote:
> The commit 93e72b3c612adcaca1 ("squashfs: migrate from ll_rw_block usage to
> BIO") removed caching of compressed blocks in SquashFS, causing fio
> performance regression in workloads with repeated file reads. Without
> caching, every read triggers disk I/O, severely impacting performance in
> tools like fio.
> 
> This patch introduces a new CONFIG_SQUASHFS_COMP_CACHE_FULL Kconfig option
> to enable caching of all compressed blocks, restoring performance to
> pre-BIO migration levels. When enabled, all pages in a BIO are cached in
> the page cache, reducing disk I/O for repeated reads. The fio test results
> with this patch confirm the performance restoration:
> 
> For example, fio tests (iodepth=1, numjobs=1,
> ioengine=psync) show a notable performance restoration:
> 
> Disable CONFIG_SQUASHFS_COMP_CACHE_FULL:
>    IOPS=815, BW=102MiB/s (107MB/s)(6113MiB/60001msec)
> Enable CONFIG_SQUASHFS_COMP_CACHE_FULL:
>    IOPS=2223, BW=278MiB/s (291MB/s)(16.3GiB/59999msec)
> 
> The trade-off is increased memory usage due to caching all compressed
> blocks. The CONFIG_SQUASHFS_COMP_CACHE_FULL option allows users to enable
> this feature selectively, balancing performance and memory usage for
> workloads with frequent repeated reads.
> 
> Signed-off-by: Chanho Min <chanho.min@....com>

Patch looks good, and I like the fact it is optional.

Reviewed-by Phillip Lougher <phillip@...ashfs.org.uk>