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

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Message-Id: <20250415231635.83960-1-dave@stgolabs.net>
Date: Tue, 15 Apr 2025 16:16:28 -0700
From: Davidlohr Bueso <dave@...olabs.net>
To: jack@...e.cz,
	tytso@....edu,
	adilger.kernel@...ger.ca,
	brauner@...nel.org
Cc: 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,
	Davidlohr Bueso <dave@...olabs.net>
Subject: [PATCH -next 0/7] fs/buffer: split pagecache lookups into atomic or blocking

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")

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