From: Christoph Hellwig <hch@infradead.org>
To: Daniel Lee <chullee@google.com>
Cc: Jaegeuk Kim <jaegeuk@kernel.org>,
linux-kernel@vger.kernel.org,
linux-f2fs-devel@lists.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH v2] f2fs: Introduce linear search for dentries
Date: Mon, 23 Dec 2024 00:26:30 -0800 [thread overview]
Message-ID: <Z2ketmZiWmUVddpt@infradead.org> (raw)
In-Reply-To: <20241220172136.1028811-1-chullee@google.com>
On Fri, Dec 20, 2024 at 09:21:36AM -0800, Daniel Lee wrote:
> This patch addresses an issue where some files in case-insensitive
> directories become inaccessible due to changes in how the kernel function,
> utf8_casefold(), generates case-folded strings from the commit 5c26d2f1d3f5
> ("unicode: Don't special case ignorable code points").
That also breaks all other direct hashed and needs to be fixed.
>
> F2FS uses these case-folded names to calculate hash values for locating
> dentries and stores them on disk. Since utf8_casefold() can produce
> different output across kernel versions, stored hash values and newly
> calculated hash values may differ. This results in affected files no
> longer being found via the hash-based lookup.
>
> To resolve this, the patch introduces a linear search fallback.
> If the initial hash-based search fails, F2FS will sequentially scan the
> directory entries.
That means you have really bad worst case behavior for negative lookups.
I don' think this is in any way a good idea.
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WARNING: multiple messages have this Message-ID (diff)
From: Christoph Hellwig <hch@infradead.org>
To: Daniel Lee <chullee@google.com>
Cc: Jaegeuk Kim <jaegeuk@kernel.org>, Chao Yu <chao@kernel.org>,
linux-f2fs-devel@lists.sourceforge.net,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] f2fs: Introduce linear search for dentries
Date: Mon, 23 Dec 2024 00:26:30 -0800 [thread overview]
Message-ID: <Z2ketmZiWmUVddpt@infradead.org> (raw)
In-Reply-To: <20241220172136.1028811-1-chullee@google.com>
On Fri, Dec 20, 2024 at 09:21:36AM -0800, Daniel Lee wrote:
> This patch addresses an issue where some files in case-insensitive
> directories become inaccessible due to changes in how the kernel function,
> utf8_casefold(), generates case-folded strings from the commit 5c26d2f1d3f5
> ("unicode: Don't special case ignorable code points").
That also breaks all other direct hashed and needs to be fixed.
>
> F2FS uses these case-folded names to calculate hash values for locating
> dentries and stores them on disk. Since utf8_casefold() can produce
> different output across kernel versions, stored hash values and newly
> calculated hash values may differ. This results in affected files no
> longer being found via the hash-based lookup.
>
> To resolve this, the patch introduces a linear search fallback.
> If the initial hash-based search fails, F2FS will sequentially scan the
> directory entries.
That means you have really bad worst case behavior for negative lookups.
I don' think this is in any way a good idea.
next prev parent reply other threads:[~2024-12-23 9:20 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-12-20 17:21 [f2fs-dev] [PATCH v2] f2fs: Introduce linear search for dentries Daniel Lee via Linux-f2fs-devel
2024-12-20 17:21 ` Daniel Lee
2024-12-20 21:00 ` [f2fs-dev] " Jaegeuk Kim via Linux-f2fs-devel
2024-12-20 21:00 ` Jaegeuk Kim
2024-12-23 8:26 ` Christoph Hellwig [this message]
2024-12-23 8:26 ` Christoph Hellwig
2024-12-23 16:57 ` [f2fs-dev] " Jaegeuk Kim via Linux-f2fs-devel
2024-12-23 16:57 ` Jaegeuk Kim
2025-01-03 9:24 ` [f2fs-dev] " Christoph Hellwig
2025-01-03 9:24 ` Christoph Hellwig
2025-01-06 21:18 ` [f2fs-dev] " Jaegeuk Kim via Linux-f2fs-devel
2025-01-06 21:18 ` Jaegeuk Kim
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