From: Roman Gushchin <guro@fb.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: <linux-mm@kvack.org>, Shakeel Butt <shakeelb@google.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Michal Hocko <mhocko@kernel.org>,
Christoph Lameter <cl@linux.com>, <linux-kernel@vger.kernel.org>,
<kernel-team@fb.com>
Subject: Re: [PATCH 2/2] mm: memcg/slab: pre-allocate obj_cgroups for slab caches with SLAB_ACCOUNT
Date: Tue, 10 Nov 2020 13:51:52 -0800 [thread overview]
Message-ID: <20201110215152.GA2713540@carbon.dhcp.thefacebook.com> (raw)
In-Reply-To: <20201110125008.003fb018e74c40109fd6723f@linux-foundation.org>
On Tue, Nov 10, 2020 at 12:50:08PM -0800, Andrew Morton wrote:
> On Tue, 10 Nov 2020 11:57:53 -0800 Roman Gushchin <guro@fb.com> wrote:
>
> > In general it's unknown in advance if a slab page will contain
> > accounted objects or not. In order to avoid memory waste, an
> > obj_cgroup vector is allocated dynamically when a need to account
> > of a new object arises. Such approach is memory efficient, but
> > requires an expensive cmpxchg() to set up the memcg/objcgs pointer,
> > because an allocation can race with a different allocation on another
> > cpu.
> >
> > But in some common cases it's known for sure that a slab page will
> > contain accounted objects: if the page belongs to a slab cache with a
> > SLAB_ACCOUNT flag set. It includes such popular objects like
> > vm_area_struct, anon_vma, task_struct, etc.
> >
> > In such cases we can pre-allocate the objcgs vector and simple assign
> > it to the page without any atomic operations, because at this early
> > stage the page is not visible to anyone else.
>
> Was there any measurable performance change from this?
A very simplistic benchmark (allocating 10000000 64-bytes objects in a row)
shows ~15% win. In the real life it seems that most workloads are not very
sensitive to the speed of (accounted) slab allocations.
next prev parent reply other threads:[~2020-11-10 21:52 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-10 19:57 [PATCH 1/2] mm: slub: call account_slab_page() after slab page initialization Roman Gushchin
2020-11-10 19:57 ` [PATCH 2/2] mm: memcg/slab: pre-allocate obj_cgroups for slab caches with SLAB_ACCOUNT Roman Gushchin
2020-11-10 20:50 ` Andrew Morton
2020-11-10 21:51 ` Roman Gushchin [this message]
2020-11-12 16:23 ` Johannes Weiner
2020-11-13 0:19 ` Roman Gushchin
2020-11-13 1:12 ` Andrew Morton
2020-11-13 1:46 ` Roman Gushchin
2020-11-16 15:03 ` Johannes Weiner
2020-11-17 17:42 ` Shakeel Butt
2020-11-17 20:15 ` Roman Gushchin
2020-11-12 15:18 ` [PATCH 1/2] mm: slub: call account_slab_page() after slab page initialization Johannes Weiner
2020-11-17 17:16 ` Shakeel Butt
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