linux-kernel - Re: [PATCH v3 1/2] f2fs: add lookup

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Message-ID: <f2f8cbd8-af49-475b-8b9c-e00250263007@kernel.org>
Date: Tue, 5 Aug 2025 14:59:56 +0800
From: Chao Yu <chao@...nel.org>
To: Daniel Lee <chullee@...gle.com>, Jaegeuk Kim <jaegeuk@...nel.org>
Cc: chao@...nel.org, linux-f2fs-devel@...ts.sourceforge.net,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/2] f2fs: add lookup_mode mount option

On 8/5/25 14:52, Daniel Lee wrote:
> For casefolded directories, f2fs may fall back to a linear search if
> a hash-based lookup fails. This can cause severe performance
> regressions.
> 
> While this behavior can be controlled by userspace tools (e.g. mkfs,
> fsck) by setting an on-disk flag, a kernel-level solution is needed
> to guarantee the lookup behavior regardless of the on-disk state.
> 
> This commit introduces the 'lookup_mode' mount option to provide this
> kernel-side control.
> 
> The option accepts three values:
> - perf: (Default) Enforces a hash-only lookup. The linear fallback
>   is always disabled.
> - compat: Enables the linear search fallback for compatibility with
>   directory entries from older kernels.
> - auto: Determines the mode based on the on-disk flag, preserving the
>   userspace-based behavior.
> 
> Signed-off-by: Daniel Lee <chullee@...gle.com>

Reviewed-by: Chao Yu <chao@...nel.org>

Thanks,