From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 37FBE3D88E3 for ; Mon, 20 Jul 2026 14:25:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784557558; cv=none; b=ucxjJw4hu7uMR7wxnO8NrqNnqQ4/JDgWKUP8Z299L3Q8fB87o3O7TlNso0V8+nyGmtqmJKFgcmO0lBfBZPO59sg2yGf5PECqF67LD/wjFSs4kbY+gucJun4nP/HTVgDIWHO16x5zY86TwREr6n/w/sI44KpTCGu9SZaNriL4yR0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784557558; c=relaxed/simple; bh=X6KBQknTcSZAj2eCcgwpoqpVuxYAtav15opjnlX4nS8=; h=Message-ID:Subject:From:To:Date:In-Reply-To:References: Content-Type:MIME-Version; b=bHx3s/FDb/Jx5T2M+gdRhEvKWZeCRVSNaVsmt4eFqIB6IFautI8PSsjUKaKlQOlpl1YnPJ7ZGh5hZ4ypYX3TS7ZMozUZHHB7vUL7yJ2etmkLRaueE15ok0+1NOq70acJqhnnT3k15fZ5N1+YwUQzIcaxYygBfp+8u97AXIAdC1A= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=CVj1PvN4; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="CVj1PvN4" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A42881F000E9; Mon, 20 Jul 2026 14:25:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784557556; bh=TXMbPozoVap2DD4MBZgOrWH3GURg6EMyvkK/QoTR/bo=; h=Subject:From:To:Date:In-Reply-To:References; b=CVj1PvN4cfL9xxFtHNJ6n3ZF9ZQvu/plPgSw0XfW6CpJQbSx/fm3zjczmhPemA7BG TRjXCfh6vkhlrFMzWWZN4kvP18VJHzTu4tueetf/CJoBUpbCseJoskgLp/Qn0vKYXW GIaANY8bhT9a4w0xo9/1WScXUXFzZo+DtN13+7EaSKpUqT66Bjtz+oFmbWciMKyFRv 5y8iKfzobMcAXiD541ObFGH4EwMz5M2zmCwxGoPJQwQr5kEK2XZf50sJ2BYipgliHF a8LBry3wAU3s3PK6ZWYdFudvVmMNh3IgDgle8RSJ98wUVMNSH7Uj3cXJUW16kYOnFf t9BcRFiTuOdHQ== Message-ID: <7107c7c9508e385b449d2e6c5a1f39d0fc7d67ee.camel@kernel.org> Subject: Re: [PATCH 0/5] allocate extent_buffer GFP_NOFAIL with unlocked retry From: Jeff Layton To: Boris Burkov , linux-btrfs@vger.kernel.org, kernel-team@fb.com Date: Mon, 20 Jul 2026 10:25:54 -0400 In-Reply-To: References: Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV T2h6v8i8YqsATFPwO4nuiTmL6I40ZofxVd+9wdRI4Db8yUNA4ZSP2nqLcLtFjClYRBoJvRWvsv4lm 0OX6MYPtv76hka8lW4mnRmZqqx3UtfHX/hF/zH24Gj7A6sYKYLCU3YrI2Ogiu7/ksKcl7goQjpvtV YrOOI5VGLHge0awt7bhMCTM9KAfPc+xL/ZxAMVWd3NCk5SamL2cE99UWgtvNOIYU8m6EjTLhsj8sn 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extent_buffer allocations in > btrfs_search_slot() done while holding btree locks. This is the single > largest category. Additionally, a large source of hung_task timeouts is > both btree waiters and direct reclaiming btree allocations, which > further motivates the desire to drive down this source of stalls and > contention. >=20 > The aim of this series is to allow us to allocate the extent_buffer, > btrfs_folio_state, and the extent_buffer folios with GFP_NOWAIT then > fallback with EAGAIN to outside the critical section to retry with > GFP_NOFS | GFP_NOFAIL without any locks held. >=20 > This is analogous to how we must drop locks to read an extent_buffer and > then EAGAIN. >=20 > The series does not manage to completely eliminate allocations from this > lock holding path, as we also allocate inside xarray functions for the > extent_buffer xarray and the btree_inode mapping xarray, the latter of > which is done via filemap_add_folio() with no reserve type API. Luckily, > those particular allocations are small cached slab allocations and have > nearly no contribution to the production reclaim fueled contention. >=20 > Boris Burkov (5): > btrfs: factor init_extent_buffer from __alloc_extent_buffer > btrfs: add struct btrfs_eb_prealloc > btrfs: enable unlocked NOFAIL retry for eb allocations > btrfs: probe with GFP_NOWAIT for tree block readahead > btrfs: use GFP_NOWAIT when inhibiting eb writeback >=20 > fs/btrfs/ctree.c | 36 ++++++- > fs/btrfs/disk-io.c | 6 +- > fs/btrfs/disk-io.h | 2 + > fs/btrfs/extent-tree.c | 6 +- > fs/btrfs/extent_io.c | 224 ++++++++++++++++++++++++++++------------- > fs/btrfs/extent_io.h | 23 +++++ > fs/btrfs/subpage.c | 7 +- > fs/btrfs/subpage.h | 3 +- > fs/btrfs/tree-log.c | 3 +- > 9 files changed, 226 insertions(+), 84 deletions(-) Nice work, Boris! This all looks good to me. You can add: Reviewed-by: Jeff Layton Note that LLM review noted a couple of minor nits you might want to address if/when you post a v2: - [N1] Dead code: commit 3 repoints the wrapper's only caller to the _pre= alloc variant, so btrfs_insert_delayed_dir_index() (kept "to preserve behavior" in commit= =C2=A02) ends the series with zero callers in-tree. Suggest removing it + its prototype in commit 3 or = a follow-up. - [N2] Latent (unreachable) leak: in btrfs_insert_dir_item, a non-NULL pr= ealloc with need_delayed_index =3D=3D false is neither committed nor freed. Only btrf= s_rename passes a prealloc and its root is never tree_root, so it can't fire today =E2=80=94 a defen= sive else if (prealloc) free would harden it.