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 31E361D1F4D for ; Mon, 21 Oct 2024 14:29:43 +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=1729520984; cv=none; b=KzfMEzmVGpgf0sKSGTkOlbKvC0tPhPP72e7aVb96XDcaUATQ66S+cCy58hoB200SuSClox5IqjlNQFLQ+61nBSmhcXsoVdGrwnZo87Vq4Bhc2XXcLKYcpKjFhVS20jekKuGtviMG4peR7XxAwtWJhFo7NmP9H9u4udF2Bo1pw74= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1729520984; c=relaxed/simple; bh=fZ/45Ohs8cURnAbn2nXRwS/pdOl0O9x4+I1lVhshw8M=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=RnteZlWQiLow3w4fd0sEV8t47Op4E6sqa3BRiZVh525AQT6eRBHp9aE+R2Cz4u3ieP9W4Eq3rC/CuCi/e49v3dKbfGs83ZqQSZLV/LgQqJ2whWLh0yBuDzRf4gf4AkKy4qMpWVwNQxLBrcfuWLpMpmvz+vI4xKW81JuLdBtvWbk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=XFQ39O0D; 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="XFQ39O0D" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 58BDDC4CEC3; Mon, 21 Oct 2024 14:29:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1729520983; bh=fZ/45Ohs8cURnAbn2nXRwS/pdOl0O9x4+I1lVhshw8M=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=XFQ39O0DzrGBmV2KWDbpS5wYaSAfBWbCjl8SUcPCmHOBBhy6ywpVpCWVYu1nvgoZJ suVmhM4aqyptD4PpQ/IOtBICF5frXxzB863t0eQoApIE1u4+HhHDj6vl6g2nAR2bQb 3m5C9kzrGgCRMVWP7WNVsQFlOXL32yQzHAukdcHdy1D3mnsMYfgiUGdzNT0f2wd6gD iwLujSwSU2QZTMorMAZQF9lHGJ8vAUieebTbBpc1f3JdKlIknOWcXayx8zqG3kUJPQ ChajnWh2f4XJaayxic1CWfoZMiLVAwbIAwNoYmjlokxr98Gky9Pj0sru6o/sW9/J+8 E/4DndsuRI9Mw== Message-ID: Subject: Re: [PATCH v2] nfs: avoid i_lock contention in nfs_clear_invalid_mapping From: Jeff Layton To: Mike Snitzer , linux-nfs@vger.kernel.org Cc: Anna Schumaker , Trond Myklebust Date: Mon, 21 Oct 2024 10:29:42 -0400 In-Reply-To: <20241018211541.42705-1-snitzer@kernel.org> References: <20241018211541.42705-1-snitzer@kernel.org> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV T2h6v8i8YqsATFPwO4nuiTmL6I40ZofxVd+9wdRI4Db8yUNA4ZSP2nqLcLtFjClYRBoJvRWvsv4lm 0OX6MYPtv76hka8lW4mnRmZqqx3UtfHX/hF/zH24Gj7A6sYKYLCU3YrI2Ogiu7/ksKcl7goQjpvtV 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nfs_clear_invalid_mapping(). >=20 > Eliminate this spinlock contention by checking flags without locking, > instead using smp_rmb and smp_load_acquire accordingly, but then take > spinlock and double-check these inode flags. >=20 > Also refactor nfs_set_cache_invalid() slightly to use > smp_store_release() to pair with nfs_clear_invalid_mapping()'s > smp_load_acquire(). >=20 > While this fix is beneficial for all multi-threaded buffered reads > issued by an NFS client, this issue was identified in the context of > surprisingly low LOCALIO performance with 4K multi-threaded buffered > read IO. This fix dramatically speeds up LOCALIO performance: >=20 > before: read: IOPS=3D1583k, BW=3D6182MiB/s (6482MB/s)(121GiB/20002msec) > after: read: IOPS=3D3046k, BW=3D11.6GiB/s (12.5GB/s)(232GiB/20001msec) >=20 > Fixes: 17dfeb911339 ("NFS: Fix races in nfs_revalidate_mapping") > Signed-off-by: Mike Snitzer > --- > fs/nfs/inode.c | 20 +++++++++++++++----- > 1 file changed, 15 insertions(+), 5 deletions(-) >=20 > v2: fix issue Jeff Layton raised, need: flags |=3D nfsi->cache_validity; >=20 > diff --git a/fs/nfs/inode.c b/fs/nfs/inode.c > index 542c7d97b235..cc7a32b32676 100644 > --- a/fs/nfs/inode.c > +++ b/fs/nfs/inode.c > @@ -205,12 +205,15 @@ void nfs_set_cache_invalid(struct inode *inode, uns= igned long flags) > nfs_fscache_invalidate(inode, 0); > flags &=3D ~NFS_INO_REVAL_FORCED; > =20 > - nfsi->cache_validity |=3D flags; > + flags |=3D nfsi->cache_validity; > + if (inode->i_mapping->nrpages =3D=3D 0) > + flags &=3D ~NFS_INO_INVALID_DATA; > =20 > - if (inode->i_mapping->nrpages =3D=3D 0) { > - nfsi->cache_validity &=3D ~NFS_INO_INVALID_DATA; > - nfs_ooo_clear(nfsi); > - } else if (nfsi->cache_validity & NFS_INO_INVALID_DATA) { > + /* pairs with nfs_clear_invalid_mapping()'s smp_load_acquire() */ > + smp_store_release(&nfsi->cache_validity, flags); > + > + if (inode->i_mapping->nrpages =3D=3D 0 || > + nfsi->cache_validity & NFS_INO_INVALID_DATA) { > nfs_ooo_clear(nfsi); > } > trace_nfs_set_cache_invalid(inode, 0); > @@ -1408,6 +1411,13 @@ int nfs_clear_invalid_mapping(struct address_space= *mapping) > TASK_KILLABLE|TASK_FREEZABLE_UNSAFE); > if (ret) > goto out; > + smp_rmb(); /* pairs with smp_wmb() below */ > + if (test_bit(NFS_INO_INVALIDATING, bitlock)) > + continue; > + /* pairs with nfs_set_cache_invalid()'s smp_store_release() */ > + if (!(smp_load_acquire(&nfsi->cache_validity) & NFS_INO_INVALID_DATA)) > + goto out; > + /* Slow-path that double-checks with spinlock held */ > spin_lock(&inode->i_lock); > if (test_bit(NFS_INO_INVALIDATING, bitlock)) { > spin_unlock(&inode->i_lock); LGTM! Reviewed-by: Jeff Layton