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

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Date:   Thu, 6 Apr 2017 17:45:23 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Michal Hocko <mhocko@...e.com>,
        "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 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?