From: Christian Brauner <brauner@kernel.org>
To: Tycho Andersen <tycho@tycho.pizza>
Cc: cgroups@vger.kernel.org, linux-fsdevel@vger.kernel.org,
Tejun Heo <tj@kernel.org>, Zefan Li <lizefan.x@bytedance.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Haitao Huang <haitao.huang@linux.intel.com>,
Kamalesh Babulal <kamalesh.babulal@oracle.com>,
Tycho Andersen <tandersen@netflix.com>
Subject: Re: [RFC 4/6] misc cgroup: introduce an fd counter
Date: Thu, 9 Nov 2023 10:53:17 +0100 [thread overview]
Message-ID: <20231108-ernst-produktiv-f0f5d2ceeade@brauner> (raw)
In-Reply-To: <20231108002647.73784-5-tycho@tycho.pizza>
> @@ -411,9 +453,22 @@ struct files_struct *dup_fd(struct files_struct *oldf, unsigned int max_fds, int
>
> rcu_assign_pointer(newf->fdt, new_fdt);
>
> - return newf;
> + if (!charge_current_fds(newf, count_open_files(new_fdt)))
> + return newf;
> @@ -542,6 +600,10 @@ static int alloc_fd(unsigned start, unsigned end, unsigned flags)
> if (error)
> goto repeat;
>
> + error = -EMFILE;
> + if (charge_current_fds(files, 1) < 0)
> + goto out;
Whoops, I had that message ready to fire but didn't send it.
This may have a noticeable performance impact as charge_current_fds()
calls misc_cg_try_charge() which looks pretty expensive in this
codepath.
We're constantly getting patches to tweak performance during file open
and closing and adding a function that does require multiple atomics and
spinlocks won't exactly improve this.
On top of that I really dislike that we're pulling cgroups into this
code here at all.
Can you get a similar effect through a bpf program somehow that you
don't even tie this to cgroups?
next prev parent reply other threads:[~2023-11-09 9:53 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-11-08 0:26 [RFC 0/6] tracking fd counts per cgroup Tycho Andersen
2023-11-08 0:26 ` [RFC 1/6] fs: count_open_files() -> count_possible_open_files() Tycho Andersen
2023-11-08 0:26 ` [RFC 2/6] fs: introduce count_open_files() Tycho Andersen
2023-11-08 0:26 ` [RFC 3/6] misc: introduce misc_cg_charge() Tycho Andersen
2023-11-08 0:26 ` [RFC 4/6] misc cgroup: introduce an fd counter Tycho Andersen
2023-11-08 16:57 ` Al Viro
2023-11-08 21:01 ` Tycho Andersen
2023-11-09 9:53 ` Christian Brauner [this message]
2023-11-09 14:58 ` Tycho Andersen
2023-11-08 0:26 ` [RFC 5/6] selftests/cgroup: add a flags arg to clone_into_cgroup() Tycho Andersen
2023-11-08 0:26 ` [RFC 6/6] selftests/cgroup: add a test for misc cgroup Tycho Andersen
2023-11-09 18:44 ` [RFC 0/6] tracking fd counts per cgroup Tejun Heo
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