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 A9839331A5A; Wed, 12 Nov 2025 12:31:58 +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=1762950718; cv=none; b=TXFbxlhPcYA9u/8q1NG42nA8bgO2piVLrW3GGGvEp6ZhpH6BPCs5/qnCmFj1ZFYQEGjMfbvXMSg/cS+tAo0ejLxzE9C2MFBP4aYajCjIpiTE40Z1jc7GNzESwbhulGAwexQFvMfhmUtVADVyeqYi/26dH/THGGZPtZITY8OFAgU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762950718; c=relaxed/simple; bh=GlKYuKsEEyi4V2HY2b7ezLSnFWQ2Pyb/BCq/tb6wv9k=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=ZaRpvht5rBEX9NKzaDdlcjvUYTyDT2q6mdxA9kdFxzQkQE4t1LQygcacE/mjfqdLFYsvfZ17PbhGCTFGgVzXXuyRyKstIefz2TKaGSFZakI1Ox3iAhuw+1shTbNwyf3jDRllBHgtIkCtUSl0J3AJKfHEmALycnh78FzfygMMnoU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=p6QGQBfF; 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="p6QGQBfF" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B7F2AC4CEF8; Wed, 12 Nov 2025 12:31:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1762950718; bh=GlKYuKsEEyi4V2HY2b7ezLSnFWQ2Pyb/BCq/tb6wv9k=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=p6QGQBfFo45yhdgOmFWmNdPNAXGoJujKk2obqH/VXsA7nBYPLNAevEsvYGaLM9Fpc 9tPag9hIk8T2GGvk5QGxRRASWyj9Pafm31liXjiUpkiWN30/r7RaWpllN2xELUzD5i 6BaqKmdcelwVqaw4f3DxGaRpBzSvbXmk7n6fd4JYaGZinnFPSvQwysWip+YDxL0wNR cq54hv4a9v64z8WHWxcxgI71vr1XO3FVc+T0JXgX14YirfZ//mi8fAEx7Nz/4IzaLV rEClr9jjSkK6xyPLRgd09wvZT2Az9UpT1QPDGoIy9/ZQAL3wkFlkN63g3bSYYAxVue ejvEFAKTGPUrw== Message-ID: <9fe596e42cbb68111901eb0354c76bdd8cd86287.camel@kernel.org> Subject: Re: [PATCH v2 2/2] fs: track the inode having file locks with a flag in ->i_opflags From: Jeff Layton To: Mateusz Guzik , brauner@kernel.org Cc: viro@zeniv.linux.org.uk, jack@suse.cz, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org Date: Wed, 12 Nov 2025 07:31:56 -0500 In-Reply-To: <20251112104432.1785404-2-mjguzik@gmail.com> References: <20251112104432.1785404-1-mjguzik@gmail.com> <20251112104432.1785404-2-mjguzik@gmail.com> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV 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Wed, 2025-11-12 at 11:44 +0100, Mateusz Guzik wrote: > Opening and closing an inode dirties the ->i_readcount field. >=20 > Depending on the alignment of the inode, it may happen to false-share > with other fields loaded both for both operations to various extent. >=20 > This notably concerns the ->i_flctx field. >=20 > Since most inodes don't have the field populated, this bit can be managed > with a flag in ->i_opflags instead which bypasses the problem. >=20 > Here are results I obtained while opening a file read-only in a loop > with 24 cores doing the work on Sapphire Rapids. Utilizing the flag as > opposed to reading ->i_flctx field was toggled at runtime as the benchmar= k > was running, to make sure both results come from the same alignment. >=20 > before: 3233740 > after: 3373346 (+4%) >=20 > before: 3284313 > after: 3518711 (+7%) >=20 > before: 3505545 > after: 4092806 (+16%) >=20 > Or to put it differently, this varies wildly depending on how (un)lucky > you get. >=20 > The primary bottleneck before and after is the avoidable lockref trip in > do_dentry_open(). >=20 > Signed-off-by: Mateusz Guzik > --- >=20 > v2: > - fix smatch warning: > ./include/linux/filelock.h:241:24: warning: Using plain integer as NULL p= ointer >=20 > fs/locks.c | 14 ++++++++++++-- > include/linux/filelock.h | 15 +++++++++++---- > include/linux/fs.h | 1 + > 3 files changed, 24 insertions(+), 6 deletions(-) >=20 > diff --git a/fs/locks.c b/fs/locks.c > index 04a3f0e20724..9cd23dd2a74e 100644 > --- a/fs/locks.c > +++ b/fs/locks.c > @@ -178,7 +178,6 @@ locks_get_lock_context(struct inode *inode, int type) > { > struct file_lock_context *ctx; > =20 > - /* paired with cmpxchg() below */ > ctx =3D locks_inode_context(inode); > if (likely(ctx) || type =3D=3D F_UNLCK) > goto out; > @@ -196,7 +195,18 @@ locks_get_lock_context(struct inode *inode, int type= ) > * Assign the pointer if it's not already assigned. If it is, then > * free the context we just allocated. > */ > - if (cmpxchg(&inode->i_flctx, NULL, ctx)) { > + spin_lock(&inode->i_lock); > + if (!(inode->i_opflags & IOP_FLCTX)) { > + VFS_BUG_ON_INODE(inode->i_flctx, inode); > + WRITE_ONCE(inode->i_flctx, ctx); > + /* > + * Paired with locks_inode_context(). > + */ > + smp_store_release(&inode->i_opflags, inode->i_opflags | IOP_FLCTX); > + spin_unlock(&inode->i_lock); Not thrilled with having to deal with the i_lock here, but this is the slow path and we typically only go through it once per inode. I can believe that IOP_FLCTX helps the more common case where the i_flctx is already present. > + } else { > + VFS_BUG_ON_INODE(!inode->i_flctx, inode); > + spin_unlock(&inode->i_lock); > kmem_cache_free(flctx_cache, ctx); > ctx =3D locks_inode_context(inode); > } > diff --git a/include/linux/filelock.h b/include/linux/filelock.h > index 37e1b33bd267..9dc57b3dcfae 100644 > --- a/include/linux/filelock.h > +++ b/include/linux/filelock.h > @@ -233,8 +233,12 @@ static inline struct file_lock_context * > locks_inode_context(const struct inode *inode) > { > /* > - * Paired with the fence in locks_get_lock_context(). > + * Paired with smp_store_release in locks_get_lock_context(). > + * > + * Ensures ->i_flctx will be visible if we spotted the flag. > */ > + if (likely(!(smp_load_acquire(&inode->i_opflags) & IOP_FLCTX))) > + return NULL; > return READ_ONCE(inode->i_flctx); > } > =20 > @@ -441,7 +445,7 @@ static inline int break_lease(struct inode *inode, un= signed int mode) > * could end up racing with tasks trying to set a new lease on this > * file. > */ > - flctx =3D READ_ONCE(inode->i_flctx); > + flctx =3D locks_inode_context(inode); > if (!flctx) > return 0; > smp_mb(); > @@ -460,7 +464,7 @@ static inline int break_deleg(struct inode *inode, un= signed int mode) > * could end up racing with tasks trying to set a new lease on this > * file. > */ > - flctx =3D READ_ONCE(inode->i_flctx); > + flctx =3D locks_inode_context(inode); > if (!flctx) > return 0; > smp_mb(); > @@ -493,8 +497,11 @@ static inline int break_deleg_wait(struct inode **de= legated_inode) > =20 > static inline int break_layout(struct inode *inode, bool wait) > { > + struct file_lock_context *flctx; > + > smp_mb(); > - if (inode->i_flctx && !list_empty_careful(&inode->i_flctx->flc_lease)) > + flctx =3D locks_inode_context(inode); > + if (flctx && !list_empty_careful(&flctx->flc_lease)) > return __break_lease(inode, > wait ? O_WRONLY : O_WRONLY | O_NONBLOCK, > FL_LAYOUT); > diff --git a/include/linux/fs.h b/include/linux/fs.h > index b803a592c07e..b3d9230c310f 100644 > --- a/include/linux/fs.h > +++ b/include/linux/fs.h > @@ -655,6 +655,7 @@ is_uncached_acl(struct posix_acl *acl) > #define IOP_MGTIME 0x0020 > #define IOP_CACHED_LINK 0x0040 > #define IOP_FASTPERM_MAY_EXEC 0x0080 > +#define IOP_FLCTX 0x0100 > =20 > /* > * Inode state bits. Protected by inode->i_lock This looks correct to me. Reviewed-by: Jeff Layton