From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 1231C47884E; Mon, 11 May 2026 18:01:34 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778522495; cv=none; b=n+iW7MhpMgX9E2uM/rFv6DRCTlR+czdRDbFjzPZxuDA3zDWxwApXaiNUb/S8KdXnJrl3B0d7Vyeb4nHh4SutfW5NDCG8L5mDeOXz0E9T8C2ght1K9+zhv4q+afkcMBXI03kCYzsCzWyTPEvzU2jkz75p9VkCVvybNPemQLSKNLo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778522495; c=relaxed/simple; bh=+Wgk0zZiISnLSWZ5QqEYYR0Csma8nlA1C1ejt+YAS58=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=YAx1Soj8taMFhx6UJaMZLWTYinRwOv6YNvyzEB8syw3kBE3Kz59kcoBq7DYGiSvqsuRMc7SoU5EH+lfZDd716sOpcFbfZKbOuigMHUq/fDWdrum5M5JeWnuMUYICdQSizaLUolUDrjzKfjXOFd6zaWubz9sifyqQLqiyfqeWt/Y= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=szoVLsiz; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="szoVLsiz" Received: by smtp.kernel.org (Postfix) with ESMTPSA id CBB67C2BCB0; Mon, 11 May 2026 18:01:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1778522494; bh=+Wgk0zZiISnLSWZ5QqEYYR0Csma8nlA1C1ejt+YAS58=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=szoVLsizLW6WEn+44BbSIv/b8rlPi3pFidC9QYIZK160X8xXMHKUSujdUr74M36Kw vG3XxndCBbNeSb25jn7g2AS5aYyJ/MMsiDRdtiStnJsYgj9iM8opEgW9J0A/W2zqdU LEFHARqqBW4naTK6kfdQIJCrsXvUkvNT88qlZ0wGjc1nuuYmn5NHtKSrQsobbcAtQT p6GKwleaXRXNXHcJnW3tNeZUv+3FsjYYjuYq7tUZhVpN8iaWX6cqzeGJt2vSxBrxVO IlsQy2oAYjmfUQA8L2eaIoPuHp7t+Qbu3W8BDZnfwB0MCva5V+LV4z2s89Bb80IbwU C4dFhQ8gpmD6A== Message-ID: <769926ac94c1565c392bc55e84cb0eb8d3c3c6f5.camel@kernel.org> Subject: Re: [PATCH v4 2/7] VFS: use wait_var_event for waiting in d_alloc_parallel() From: Jeff Layton To: NeilBrown , Linus Torvalds , Al Viro , Christian Brauner , Jan Kara , Amir Goldstein Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Date: Mon, 11 May 2026 14:01:31 -0400 In-Reply-To: <20260430020137.3305302-3-neilb@ownmail.net> References: <20260430020137.3305302-1-neilb@ownmail.net> <20260430020137.3305302-3-neilb@ownmail.net> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV 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Thu, 2026-04-30 at 11:56 +1000, NeilBrown wrote: > From: NeilBrown >=20 > d_alloc_parallel() currently requires a wait_queue_head to be passed in. > This must have a life time which extends until the lookup is completed. >=20 > This makes it awkward to use and particularly make it hard to use in > lookup_one_qstr_excl() which I hope to do in the future. >=20 > This patch changes d_alloc_parallel() to use wake_up_var_locked() to > wake up waiters, and wait_var_event_spinlock() to wait. dentry->d_lock > is used for synchronisation as it is already held and the relevant > times. >=20 > In most cases there will be no waiters so the wake_up_var_locked() call > (which can walk an arbitrarily long list) would be a complete waste. To > optimise this a new ->d_flags flag is added: DCACHE_LOOKUP_WAITER. This > is set whenever any thread prepares to wait for the dentry, and if it > isn't set when DCACHE_PAR_LOOKUP is cleared, no wakeup is sent. > DCACHE_LOOKUP_WAITER is cleared after the wakeup is set. >=20 > __d_lookup_unhash() no longer returns a wq. Callers check > DCACHE_LOOKUP_WAITER to check if a wakeup is needed, and > wake_up_var_locked() can find the wq. >=20 > __d_lookup_unhash() no longer needs to re-init ->d_lru. That was > previously shared (in a union) with ->d_wait but ->d_wait is now gone > so it no longer corrupts ->d_lru. >=20 > Wakeup is move out of end_dir_add() as it is conceptually a separate acti= on. >=20 > Co-developed-by: Al Viro > Signed-off-by: Al Viro > Signed-off-by: NeilBrown > --- > Documentation/filesystems/porting.rst | 6 ++ > fs/afs/dir_silly.c | 4 +- > fs/dcache.c | 83 +++++++++++++++------------ > fs/fuse/readdir.c | 3 +- > fs/namei.c | 6 +- > fs/nfs/dir.c | 6 +- > fs/nfs/unlink.c | 3 +- > fs/proc/base.c | 3 +- > fs/proc/proc_sysctl.c | 3 +- > fs/smb/client/readdir.c | 3 +- > include/linux/dcache.h | 11 ++-- > include/linux/nfs_xdr.h | 1 - > 12 files changed, 67 insertions(+), 65 deletions(-) >=20 >=20 [...] > =20 > @@ -2979,7 +2987,7 @@ static void __d_move(struct dentry *dentry, struct = dentry *target, > if (unlikely(d_in_lookup(target))) { > dir =3D target->d_parent->d_inode; > n =3D start_dir_add(dir); > - d_wait =3D __d_lookup_unhash(target); > + __d_lookup_unhash(target); > } In the old code, d_wait was associated with the target... > =20 > write_seqcount_begin(&dentry->d_seq); > @@ -3018,9 +3026,10 @@ static void __d_move(struct dentry *dentry, struct= dentry *target, > write_seqcount_end(&target->d_seq); > write_seqcount_end(&dentry->d_seq); > =20 > - if (dir) > - end_dir_add(dir, n, d_wait); > - > + if (dir) { > + end_dir_add(dir, n); > + __d_wake_in_lookup_waiters(dentry); > + } ...but here you are waking based on "dentry". Should that be: __d_wake_in_lookup_waiters(target) ? --=20 Jeff Layton