Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   Roman Gushchin <guro@fb.com>
To:     Andrew Morton <akpm@linux-foundation.org>
CC:     Roman Gushchin <guroan@gmail.com>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Kernel Team <Kernel-team@fb.com>,
        "Matthew Wilcox" <willy@infradead.org>,
        Johannes Weiner <hannes@cmpxchg.org>,
        "Vlastimil Babka" <vbabka@suse.cz>
Subject: Re: [PATCH v4 1/2] mm: refactor __vunmap() to avoid duplicated call
 to find_vm_area()
Thread-Topic: [PATCH v4 1/2] mm: refactor __vunmap() to avoid duplicated call
 to find_vm_area()
Thread-Index: AQHU9VVf0J9odzgRMk2KdtJT9GHQdKZA5rSAgAAR2wA=
Date:   Wed, 17 Apr 2019 23:02:25 +0000
Message-ID: <20190417230219.GA5538@tower.DHCP.thefacebook.com>
References: <20190417194002.12369-1-guro@fb.com>
 <20190417194002.12369-2-guro@fb.com>
 <20190417145827.8b1c83bf22de8ba514f157e3@linux-foundation.org>
In-Reply-To: <20190417145827.8b1c83bf22de8ba514f157e3@linux-foundation.org>
Accept-Language: en-US
Content-Language: en-US
x-ms-exchange-messagesentrepresentingtype: 1
x-originating-ip: [2620:10d:c090:200::1:7270]
x-ms-publictraffictype: Email
x-ms-office365-filtering-correlation-id: 356c02f2-6f66-4a70-7791-08d6c388c1b1
x-microsoft-antispam: BCL:0;PCL:0;RULEID:(2390118)(7020095)(4652040)(8989299)(5600141)(711020)(4605104)(4534185)(4627221)(201703031133081)(201702281549075)(8990200)(2017052603328)(7193020);SRVR:BYAPR15MB3190;
x-ms-traffictypediagnostic: BYAPR15MB3190:
x-microsoft-antispam-prvs: <BYAPR15MB3190FF362FBA5B9062AA9356BE250@BYAPR15MB3190.namprd15.prod.outlook.com>
x-forefront-prvs: 0010D93EFE
x-forefront-antispam-report: SFV:NSPM;SFS:(10019020)(376002)(346002)(396003)(136003)(39860400002)(366004)(199004)(189003)(25786009)(6916009)(71190400001)(71200400001)(476003)(6486002)(5660300002)(46003)(54906003)(11346002)(8676002)(486006)(97736004)(478600001)(86362001)(1076003)(6436002)(316002)(53546011)(6506007)(256004)(6512007)(6246003)(6116002)(14444005)(446003)(186003)(386003)(81156014)(81166006)(53936002)(8936002)(102836004)(7736002)(229853002)(4326008)(52116002)(2906002)(68736007)(33656002)(9686003)(76176011)(305945005)(99286004)(14454004)(37363001);DIR:OUT;SFP:1102;SCL:1;SRVR:BYAPR15MB3190;H:BYAPR15MB2631.namprd15.prod.outlook.com;FPR:;SPF:None;LANG:en;PTR:InfoNoRecords;A:1;MX:1;
received-spf: None (protection.outlook.com: fb.com does not designate
 permitted sender hosts)
x-ms-exchange-senderadcheck: 1
x-microsoft-antispam-message-info: M72ARGDIpm80FoZXz9ldgVyLzaT3sBSixZt4G4J7xGTf6Zc+oHddh56PLAwmYH4wA9ernKV6zwD9zknni5VWbYbghWGU9rowWyvWOChJZa9Pg3Y5GiohB3h1m+mjA5cngTfA+FY2ujsYiTuz76vGZHHEMTLpoEEjiSPSi0nfyoj4BSShbqPx4EiURnf/9Gi1yMe7CuhU8QJjVXNFemly/Et68nZ893/wiPSlf5P368RyssoO6DzNJHv/1Z7HjzNcebwZ8VN6h5hCSwuAsdr9nLlymH8vsytYPq4TxHJ1vXRbexp80e6gZ2L81CGHNEwtOh6JTqLRMm79ztisenn7qZbVD59yVeGisTh7imw9PdBnKKwuV/DEUuDtghPfJDUSku+VTSTyjWSVDZFuJmRZbPELEkz24TfhFOsvQTxbk0M=
Content-Type: text/plain; charset="us-ascii"
Content-ID: <2B6F40F0B437D94AA8B7732ED7F6698B@namprd15.prod.outlook.com>
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0
X-MS-Exchange-CrossTenant-Network-Message-Id: 356c02f2-6f66-4a70-7791-08d6c388c1b1
X-MS-Exchange-CrossTenant-originalarrivaltime: 17 Apr 2019 23:02:25.5428
 (UTC)
X-MS-Exchange-CrossTenant-fromentityheader: Hosted
X-MS-Exchange-CrossTenant-id: 8ae927fe-1255-47a7-a2af-5f3a069daaa2
X-MS-Exchange-CrossTenant-mailboxtype: HOSTED
X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR15MB3190
X-OriginatorOrg: fb.com
X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-04-17_11:,,
 signatures=0
X-Proofpoint-Spam-Reason: safe
X-FB-Internal: Safe
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Wed, Apr 17, 2019 at 02:58:27PM -0700, Andrew Morton wrote:
> On Wed, 17 Apr 2019 12:40:01 -0700 Roman Gushchin <guroan@gmail.com> wrot=
e:
>=20
> > __vunmap() calls find_vm_area() twice without an obvious reason:
> > first directly to get the area pointer, second indirectly by calling
> > remove_vm_area(), which is again searching for the area.
> >=20
> > To remove this redundancy, let's split remove_vm_area() into
> > __remove_vm_area(struct vmap_area *), which performs the actual area
> > removal, and remove_vm_area(const void *addr) wrapper, which can
> > be used everywhere, where it has been used before.
> >=20
> > On my test setup, I've got 5-10% speed up on vfree()'ing 1000000
> > of 4-pages vmalloc blocks.
> >=20
> > Perf report before:
> >   22.64%  cat      [kernel.vmlinux]  [k] free_pcppages_bulk
> >   10.30%  cat      [kernel.vmlinux]  [k] __vunmap
> >    9.80%  cat      [kernel.vmlinux]  [k] find_vmap_area
> >    8.11%  cat      [kernel.vmlinux]  [k] vunmap_page_range
> >    4.20%  cat      [kernel.vmlinux]  [k] __slab_free
> >    3.56%  cat      [kernel.vmlinux]  [k] __list_del_entry_valid
> >    3.46%  cat      [kernel.vmlinux]  [k] smp_call_function_many
> >    3.33%  cat      [kernel.vmlinux]  [k] kfree
> >    3.32%  cat      [kernel.vmlinux]  [k] free_unref_page
> >=20
> > Perf report after:
> >   23.01%  cat      [kernel.kallsyms]  [k] free_pcppages_bulk
> >    9.46%  cat      [kernel.kallsyms]  [k] __vunmap
> >    9.15%  cat      [kernel.kallsyms]  [k] vunmap_page_range
> >    6.17%  cat      [kernel.kallsyms]  [k] __slab_free
> >    5.61%  cat      [kernel.kallsyms]  [k] kfree
> >    4.86%  cat      [kernel.kallsyms]  [k] bad_range
> >    4.67%  cat      [kernel.kallsyms]  [k] free_unref_page_commit
> >    4.24%  cat      [kernel.kallsyms]  [k] __list_del_entry_valid
> >    3.68%  cat      [kernel.kallsyms]  [k] free_unref_page
> >    3.65%  cat      [kernel.kallsyms]  [k] __list_add_valid
> >    3.19%  cat      [kernel.kallsyms]  [k] __purge_vmap_area_lazy
> >    3.10%  cat      [kernel.kallsyms]  [k] find_vmap_area
> >    3.05%  cat      [kernel.kallsyms]  [k] rcu_cblist_dequeue
> >=20
> > ...
> >
> > --- a/mm/vmalloc.c
> > +++ b/mm/vmalloc.c
> > @@ -2068,6 +2068,24 @@ struct vm_struct *find_vm_area(const void *addr)
> >  	return NULL;
> >  }
> > =20
> > +static struct vm_struct *__remove_vm_area(struct vmap_area *va)
> > +{
> > +	struct vm_struct *vm =3D va->vm;
> > +
> > +	might_sleep();
>=20
> Where might __remove_vm_area() sleep?
>=20
> From a quick scan I'm only seeing vfree(), and that has the
> might_sleep_if(!in_interrupt()).
>=20
> So perhaps we can remove this...

Agree. Here is the patch.

Thank you!

--

From 4adf58e4d3ffe45a542156ca0bce3dc9f6679939 Mon Sep 17 00:00:00 2001
From: Roman Gushchin <guro@fb.com>
Date: Wed, 17 Apr 2019 15:55:49 -0700
Subject: [PATCH] mm: remove might_sleep() in __remove_vm_area()

__remove_vm_area() has a redundant might_sleep() call, which isn't
really required, because the only place it can sleep is vfree()
and it already contains might_sleep_if(!in_interrupt()).

Suggested-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Roman Gushchin <guro@fb.com>
---
 mm/vmalloc.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 69a5673c4cd3..4a91acce4b5f 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -2079,8 +2079,6 @@ static struct vm_struct *__remove_vm_area(struct vmap=
_area *va)
 {
 	struct vm_struct *vm =3D va->vm;
=20
-	might_sleep();
-
 	spin_lock(&vmap_area_lock);
 	va->vm =3D NULL;
 	va->flags &=3D ~VM_VM_AREA;
--=20
2.20.1