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 AC4A31D3656; Thu, 21 Nov 2024 14:16:21 +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=1732198581; cv=none; b=WVgN3S9dcgzWHaydWYeT/BTw0gK8o1bhh15JK9olFrSr8XuLDJ1Ney+XNy29qJn/4FRIggkABrfUQm/dPpzHEScOcSpakzBqmf34aEWQB056VzPBYFj4ra7T1S4lYMhcqnQxV2tGLavCn+POn+YUSwZGnr12y4KRob1u+sc2RMk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732198581; c=relaxed/simple; bh=jpRTGVKAEwCkyxmVL8MPJVCxOWSyQ5Jpjt2erQeCglE=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=eLqfnPE3Tz9Ek2Af5MR+CpxjbuuhqW9g7Qzl80pFBzgSt3R2JtGLlMC3/VA/qjD6FKAqvpbELwESwYa8kBvvYqMzH8h8BxmdohzG9C3WwUSuvVt8F9dJnquZU3UW6ZJj6ZaJRN7/aRn4L/Rr2/4mSOXWblFbGMyjRKOeOgN7uFo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=teYXSNKx; 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="teYXSNKx" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 58E5DC4CECC; Thu, 21 Nov 2024 14:16:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1732198581; bh=jpRTGVKAEwCkyxmVL8MPJVCxOWSyQ5Jpjt2erQeCglE=; h=Subject:From:To:Cc:Date:In-Reply-To:References:From; b=teYXSNKxIyi6O6wd2h+LHvtdEYDtZwLIlqUt8YXWePyEECs0IaLvLSQlOdXoZb9Xp PezHAUIZ7tHwYZPHuQdb+zU2/hGlk3QjhcsqBxaMkDkJnpq+yXgpu7Cn5L7bmUjDxs igIX1HpdvKd+47U6ZI9KIJy6mhD2NsrbxgN47911G3IZyRbuvpvyu6PbwXMgZ/7bR3 wMAYcP2mzqi6VAvUF6ynWnR9XxvNuFR1CYxibCSbKPcPpwQud7Q3wblVPqIFV7UlhI s/NUYPx7/q62XqXTaS03BhkzApQDLrhGvSYizpt2jNo3PFuxX2Oh3vws+ChPkesIak C2EIbijWTn5tg== Message-ID: Subject: Re: [PATCH v3 0/3] symlink length caching 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, hughd@google.com, linux-ext4@vger.kernel.org, tytso@mit.edu, linux-mm@kvack.org Date: Thu, 21 Nov 2024 09:16:19 -0500 In-Reply-To: <20241120112037.822078-1-mjguzik@gmail.com> References: <20241120112037.822078-1-mjguzik@gmail.com> Autocrypt: addr=jlayton@kernel.org; prefer-encrypt=mutual; keydata=mQINBE6V0TwBEADXhJg7s8wFDwBMEvn0qyhAnzFLTOCHooMZyx7XO7dAiIhDSi7G1NPxw n8jdFUQMCR/GlpozMFlSFiZXiObE7sef9rTtM68ukUyZM4pJ9l0KjQNgDJ6Fr342Htkjxu/kFV1Wv egyjnSsFt7EGoDjdKqr1TS9syJYFjagYtvWk/UfHlW09X+jOh4vYtfX7iYSx/NfqV3W1D7EDi0PqV T2h6v8i8YqsATFPwO4nuiTmL6I40ZofxVd+9wdRI4Db8yUNA4ZSP2nqLcLtFjClYRBoJvRWvsv4lm 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it dodges strlen() in vfs_readlink(), giving about 1.5% > speed up when issuing readlink on /initrd.img on ext4. >=20 > The size is stored in a union with i_devices, which is never looked at > unless the inode is for a device. >=20 > Benchmark code at the bottom. >=20 > ext4 and tmpfs are patched, other filesystems can also get there with > some more work. >=20 > Arguably the current get_link API should be patched to let the fs return > the size, but that's not a churn I'm interested into diving in. >=20 > On my v1 Jan remarked 1.5% is not a particularly high win questioning > whether doing this makes sense. I noted the value is only this small > because of other slowdowns. >=20 > To elaborate here are highlights while benching on Sapphire Rapids: > 1. putname using atomics (over 3.5% on my profile) >=20 > sounds like Al has plans to do something here(?), I'm not touching it if > it can be helped. the atomic definitely does not have to be there in the > common case. >=20 > 2. kmem_cache_alloc_noprof/kmem_cache_free (over 7% combined)=20 >=20 > They are both dog slow due to cmpxchg16b. A patchset was posted which > adds a different allocation/free fast path which should whack majority > of the problem, see: https://lore.kernel.org/linux-mm/20241112-slub-percp= u-caches-v1-0-ddc0bdc27e05@suse.cz/ >=20 > If this lands I'll definitely try to make the pathname allocs use it, > should drop about 5-6 percentage points on this sucker. >=20 > 3. __legitimize_mnt issues a full fence (again over 3%) >=20 > As far as avoiding the fence is concerned waiting on rcu grace period on > unmount should do the trick. However, I found there is a bunch > complexity there to sort out before doing this will be feasible (notably > there are multiple mounts freed in one go, this needs to be batched). > There may be other issues which I missed and which make this not worth > it, but the fence is definitely avoidable in principle and I would be > surprised if there was no way to sensibly get there. No ETA, for now I'm > just pointing this out. >=20 > There is also the idea to speculatively elide lockref, but when I tried > that last time I ran into significant LSM-related trouble. >=20 > All that aside there is also quite a bit of branching and func calling > which does not need to be there (example: make vfsuid/vfsgid, could be > combined into one routine etc.). >=20 > Ultimately there is single-threaded perf left on the table in various > spots. >=20 > v3: > - use a union instead of a dedicated field, used up with i_devices >=20 > v2: > - add a dedicated field, flag and a helper instead of using i_size > https://lore.kernel.org/linux-fsdevel/20241119094555.660666-1-mjguzik@gma= il.com/ >=20 > v1 can be found here: > https://lore.kernel.org/linux-fsdevel/20241118085357.494178-1-mjguzik@gma= il.com/ >=20 > benchmark: > plug into will-it-scale into tests/readlink1.c: >=20 > #include > #include > #include > #include > #include > #include > #include >=20 > char *testcase_description =3D "readlink /initrd.img"; >=20 > void testcase(unsigned long long *iterations, unsigned long nr) > { > char *tmplink =3D "/initrd.img"; > char buf[1024]; >=20 > while (1) { > int error =3D readlink(tmplink, buf, sizeof(buf)); > assert(error > 0); >=20 > (*iterations)++; > } > } >=20 > Mateusz Guzik (3): > vfs: support caching symlink lengths in inodes > ext4: use inode_set_cached_link() > tmpfs: use inode_set_cached_link() >=20 > fs/ext4/inode.c | 3 ++- > fs/ext4/namei.c | 4 +++- > fs/namei.c | 34 +++++++++++++++++++--------------- > fs/proc/namespaces.c | 2 +- > include/linux/fs.h | 15 +++++++++++++-- > mm/shmem.c | 6 ++++-- > security/apparmor/apparmorfs.c | 2 +- > 7 files changed, 43 insertions(+), 23 deletions(-) >=20 Nice work, Mateusz! Reviewed-by: Jeff Layton