linux-kernel - Re: [PATCH 2/9] mm: support __GFP_REPEAT in kvmalloc

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Message-ID: <20170407074001.GB16413@dhcp22.suse.cz>
Date:   Fri, 7 Apr 2017 09:40:01 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Shakeel Butt <shakeelb@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH 2/9] mm: support __GFP_REPEAT in kvmalloc_node for >32kB

On Thu 06-04-17 17:45:23, Shakeel Butt wrote:
> On Mon, Mar 6, 2017 at 2:30 AM, Michal Hocko <mhocko@...nel.org> wrote:
> > From: Michal Hocko <mhocko@...e.com>
> >
> > vhost code uses __GFP_REPEAT when allocating vhost_virtqueue resp.
> > vhost_vsock because it would really like to prefer kmalloc to the
> > vmalloc fallback - see 23cc5a991c7a ("vhost-net: extend device
> > allocation to vmalloc") for more context. Michael Tsirkin has also
> > noted:
> > "
> > __GFP_REPEAT overhead is during allocation time.  Using vmalloc means all
> > accesses are slowed down.  Allocation is not on data path, accesses are.
> > "
> >
> > The similar applies to other vhost_kvzalloc users.
> >
> > Let's teach kvmalloc_node to handle __GFP_REPEAT properly. There are two
> > things to be careful about. First we should prevent from the OOM killer
> > and so have to involve __GFP_NORETRY by default and secondly override
> > __GFP_REPEAT for !costly order requests as the __GFP_REPEAT is ignored
> > for !costly orders.
> >
> > Supporting __GFP_REPEAT like semantic for !costly request is possible
> > it would require changes in the page allocator. This is out of scope of
> > this patch.
> >
> > This patch shouldn't introduce any functional change.
> >
> > Acked-by: Vlastimil Babka <vbabka@...e.cz>
> > Acked-by: Michael S. Tsirkin <mst@...hat.com>
> > Signed-off-by: Michal Hocko <mhocko@...e.com>
> > ---
> >  drivers/vhost/net.c   |  9 +++------
> >  drivers/vhost/vhost.c | 15 +++------------
> >  drivers/vhost/vsock.c |  9 +++------
> >  mm/util.c             | 20 ++++++++++++++++----
> >  4 files changed, 25 insertions(+), 28 deletions(-)
> >
> 
> There is a kzalloc/vzalloc call in
> drivers/vhost/scsi.c:vhost_scsi_open() which is not converted to
> kvzalloc(). Was that intentional?

No, an omission, I suspect. Feel free to send a follow up patch. I
suspect there will be more of those...

-- 
Michal Hocko
SUSE Labs