linux-ext4 - Re: [PATCH -next 0/7] fs/buffer: split pagecache lookups into atomic or blocking

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Message-ID: <20250417-jagdhund-ruhmreich-f1c979cdd58d@brauner>
Date: Thu, 17 Apr 2025 11:58:12 +0200
From: Christian Brauner <brauner@...nel.org>
To: Davidlohr Bueso <dave@...olabs.net>
Cc: jack@...e.cz, tytso@....edu, adilger.kernel@...ger.ca, 
	mcgrof@...nel.org, willy@...radead.org, hare@...e.de, djwong@...nel.org, 
	linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH -next 0/7] fs/buffer: split pagecache lookups into atomic
 or blocking

On Tue, Apr 15, 2025 at 04:16:28PM -0700, Davidlohr Bueso wrote:
> Hello,
> 
> This is a respin of the series[0] to address the sleep in atomic scenarios for
> noref migration with large folios, introduced in:
> 
>       3c20917120ce61 ("block/bdev: enable large folio support for large logical block sizes")

Please resend based on vfs.fixes.

> The main difference is that it removes the first patch and moves the fix (reducing
> the i_private_lock critical region in the migration path) to the final patch, which
> also introduces the new BH_Migrate flag. It also simplifies the locking scheme in
> patch 1 to avoid folio trylocking in the atomic lookup cases. So essentially blocking
> users will take the folio lock and hence wait for migration, and otherwise nonblocking
> callers will bail the lookup if a noref migration is on-going. Blocking callers
> will also benefit from potential performance gains by reducing contention on the
> spinlock for bdev mappings.
> 
> It is noteworthy that this series is probably too big for Linus' tree, so there are
> two options:
> 
>  1. Revert 3c20917120ce61, add this series + 3c20917120ce61 for next. Or,
>  2. Cherry pick patch 7 as a fix for Linus' tree, and leave the rest for next.
>     But that could break lookup callers that have been deemed unfit to bail.
> 
> Patch 1: carves a path for callers that can block to take the folio lock.
> Patch 2: adds sleeping flavors to pagecache lookups, no users.
> Patches 3-6: converts to the new call, where possible.
> Patch 7: does the actual sleep in atomic fix.
> 
> Thanks!
> 
> [0] https://lore.kernel.org/all/20250410014945.2140781-1-mcgrof@kernel.org/
> 
> Davidlohr Bueso (7):
>   fs/buffer: split locking for pagecache lookups
>   fs/buffer: introduce sleeping flavors for pagecache lookups
>   fs/buffer: use sleeping version of __find_get_block()
>   fs/ocfs2: use sleeping version of __find_get_block()
>   fs/jbd2: use sleeping version of __find_get_block()
>   fs/ext4: use sleeping version of sb_find_get_block()
>   mm/migrate: fix sleep in atomic for large folios and buffer heads
> 
>  fs/buffer.c                 | 73 +++++++++++++++++++++++++++----------
>  fs/ext4/ialloc.c            |  3 +-
>  fs/ext4/mballoc.c           |  3 +-
>  fs/jbd2/revoke.c            | 15 +++++---
>  fs/ocfs2/journal.c          |  2 +-
>  include/linux/buffer_head.h |  9 +++++
>  mm/migrate.c                |  8 ++--
>  7 files changed, 82 insertions(+), 31 deletions(-)
> 
> --
> 2.39.5
>