linux-kernel - Re: [PATCH AUTOSEL 6.12 25/37] fs/buffer: split locking for pagecache lookups

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Message-ID: <aBFzbF_kRJAawSkE@bombadil.infradead.org>
Date: Tue, 29 Apr 2025 17:48:44 -0700
From: Luis Chamberlain <mcgrof@...nel.org>
To: Sasha Levin <sashal@...nel.org>
Cc: linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	Davidlohr Bueso <dave@...olabs.net>, Jan Kara <jack@...e.cz>,
	kdevops@...ts.linux.dev, Christian Brauner <brauner@...nel.org>,
	viro@...iv.linux.org.uk, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH AUTOSEL 6.12 25/37] fs/buffer: split locking for
 pagecache lookups

On Tue, Apr 29, 2025 at 07:51:10PM -0400, Sasha Levin wrote:
> From: Davidlohr Bueso <dave@...olabs.net>
> 
> [ Upstream commit 7ffe3de53a885dbb5836541c2178bd07d1bad7df ]
> 
> Callers of __find_get_block() may or may not allow for blocking
> semantics, and is currently assumed that it will not. Layout
> two paths based on this. The the private_lock scheme will
> continued to be used for atomic contexts. Otherwise take the
> folio lock instead, which protects the buffers, such as
> vs migration and try_to_free_buffers().
> 
> Per the "hack idea", the latter can alleviate contention on
> the private_lock for bdev mappings. For reasons of determinism
> and avoid making bugs hard to reproduce, the trylocking is not
> attempted.
> 
> No change in semantics. All lookup users still take the spinlock.
> 
> Reviewed-by: Jan Kara <jack@...e.cz>
> Signed-off-by: Davidlohr Bueso <dave@...olabs.net>
> Link: https://kdevops.org/ext4/v6.15-rc2.html # [0]
> Link: https://lore.kernel.org/all/aAAEvcrmREWa1SKF@bombadil.infradead.org/ # [1]
> Link: https://lore.kernel.org/20250418015921.132400-2-dave@stgolabs.net
> Tested-by: kdevops@...ts.linux.dev
> Reviewed-by: Luis Chamberlain <mcgrof@...nel.org>
> Signed-off-by: Christian Brauner <brauner@...nel.org>
> Signed-off-by: Sasha Levin <sashal@...nel.org>

Same no way. This is pushing it.

  Luis