linux-kernel - Re: [PATCH v2] mm: mmap_lock: optimize mmap

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <CAJHvVcg_mHiGvMpaM5XX8F7cvsxxGc9oOdCsy4zjMJAd9kX8-A@mail.gmail.com>
Date: Wed, 27 Nov 2024 12:09:42 -0800
From: Axel Rasmussen <axelrasmussen@...gle.com>
To: Roman Gushchin <roman.gushchin@...ux.dev>
Cc: Shakeel Butt <shakeel.butt@...ux.dev>, Andrew Morton <akpm@...ux-foundation.org>, 
	Johannes Weiner <hannes@...xchg.org>, Michal Hocko <mhocko@...nel.org>, 
	Muchun Song <muchun.song@...ux.dev>, Vlastimil Babka <vbabka@...e.cz>, 
	Steven Rostedt <rostedt@...dmis.org>, Suren Baghdasaryan <surenb@...gle.com>, 
	Matthew Wilcox <willy@...radead.org>, linux-mm@...ck.org, cgroups@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Meta kernel team <kernel-team@...a.com>
Subject: Re: [PATCH v2] mm: mmap_lock: optimize mmap_lock tracepoints

No objections. :)

Reviewed-by: Axel Rasmussen <axelrasmussen@...gle.com>


On Tue, Nov 26, 2024 at 11:29 AM Roman Gushchin
<roman.gushchin@...ux.dev> wrote:
>
> On Mon, Nov 25, 2024 at 09:16:17AM -0800, Shakeel Butt wrote:
> > We are starting to deploy mmap_lock tracepoint monitoring across our
> > fleet and the early results showed that these tracepoints are consuming
> > significant amount of CPUs in kernfs_path_from_node when enabled.
> >
> > It seems like the kernel is trying to resolve the cgroup path in the
> > fast path of the locking code path when the tracepoints are enabled. In
> > addition for some application their metrics are regressing when
> > monitoring is enabled.
> >
> > The cgroup path resolution can be slow and should not be done in the
> > fast path. Most userspace tools, like bpftrace, provides functionality
> > to get the cgroup path from cgroup id, so let's just trace the cgroup
> > id and the users can use better tools to get the path in the slow path.
> >
> > Signed-off-by: Shakeel Butt <shakeel.butt@...ux.dev>
>
> Acked-by: Roman Gushchin <roman.gushchin@...ux.dev>
>
> Thanks!