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Message-ID: <20170112181142-mutt-send-email-mst@kernel.org>
Date: Thu, 12 Jan 2017 18:12:01 +0200
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Michal Hocko <mhocko@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Vlastimil Babka <vbabka@...e.cz>,
David Rientjes <rientjes@...gle.com>,
Mel Gorman <mgorman@...e.de>,
Johannes Weiner <hannes@...xchg.org>,
Al Viro <viro@...iv.linux.org.uk>, linux-mm@...ck.org,
LKML <linux-kernel@...r.kernel.org>,
Michal Hocko <mhocko@...e.com>
Subject: Re: [PATCH 2/6] mm: support __GFP_REPEAT in kvmalloc_node for >=64kB
On Thu, Jan 12, 2017 at 04:37:13PM +0100, Michal Hocko 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.
>
> Cc: "Michael S. Tsirkin" <mst@...hat.com>
> Acked-by: Vlastimil Babka <vbabka@...e.cz>
> Signed-off-by: Michal Hocko <mhocko@...e.com>
Acked-by: Michael S. Tsirkin <mst@...hat.com>
> ---
> drivers/vhost/net.c | 9 +++------
> drivers/vhost/vhost.c | 15 +++------------
> drivers/vhost/vsock.c | 9 +++------
> mm/util.c | 17 ++++++++++++++---
> 4 files changed, 23 insertions(+), 27 deletions(-)
>
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index 5dc34653274a..105cd04c7414 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -797,12 +797,9 @@ static int vhost_net_open(struct inode *inode, struct file *f)
> struct vhost_virtqueue **vqs;
> int i;
>
> - n = kmalloc(sizeof *n, GFP_KERNEL | __GFP_NOWARN | __GFP_REPEAT);
> - if (!n) {
> - n = vmalloc(sizeof *n);
> - if (!n)
> - return -ENOMEM;
> - }
> + n = kvmalloc(sizeof *n, GFP_KERNEL | __GFP_REPEAT);
> + if (!n)
> + return -ENOMEM;
> vqs = kmalloc(VHOST_NET_VQ_MAX * sizeof(*vqs), GFP_KERNEL);
> if (!vqs) {
> kvfree(n);
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index d6432603880c..d2bf8a41f55e 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -515,18 +515,9 @@ long vhost_dev_set_owner(struct vhost_dev *dev)
> }
> EXPORT_SYMBOL_GPL(vhost_dev_set_owner);
>
> -static void *vhost_kvzalloc(unsigned long size)
> -{
> - void *n = kzalloc(size, GFP_KERNEL | __GFP_NOWARN | __GFP_REPEAT);
> -
> - if (!n)
> - n = vzalloc(size);
> - return n;
> -}
> -
> struct vhost_umem *vhost_dev_reset_owner_prepare(void)
> {
> - return vhost_kvzalloc(sizeof(struct vhost_umem));
> + return kvzalloc(sizeof(struct vhost_umem), GFP_KERNEL);
> }
> EXPORT_SYMBOL_GPL(vhost_dev_reset_owner_prepare);
>
> @@ -1190,7 +1181,7 @@ EXPORT_SYMBOL_GPL(vhost_vq_access_ok);
>
> static struct vhost_umem *vhost_umem_alloc(void)
> {
> - struct vhost_umem *umem = vhost_kvzalloc(sizeof(*umem));
> + struct vhost_umem *umem = kvzalloc(sizeof(*umem), GFP_KERNEL);
>
> if (!umem)
> return NULL;
> @@ -1216,7 +1207,7 @@ static long vhost_set_memory(struct vhost_dev *d, struct vhost_memory __user *m)
> return -EOPNOTSUPP;
> if (mem.nregions > max_mem_regions)
> return -E2BIG;
> - newmem = vhost_kvzalloc(size + mem.nregions * sizeof(*m->regions));
> + newmem = kvzalloc(size + mem.nregions * sizeof(*m->regions), GFP_KERNEL);
> if (!newmem)
> return -ENOMEM;
>
> diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
> index bbbf588540ed..7e0159867553 100644
> --- a/drivers/vhost/vsock.c
> +++ b/drivers/vhost/vsock.c
> @@ -455,12 +455,9 @@ static int vhost_vsock_dev_open(struct inode *inode, struct file *file)
> /* This struct is large and allocation could fail, fall back to vmalloc
> * if there is no other way.
> */
> - vsock = kzalloc(sizeof(*vsock), GFP_KERNEL | __GFP_NOWARN | __GFP_REPEAT);
> - if (!vsock) {
> - vsock = vmalloc(sizeof(*vsock));
> - if (!vsock)
> - return -ENOMEM;
> - }
> + vsock = kvmalloc(sizeof(*vsock), GFP_KERNEL | __GFP_REPEAT);
> + if (!vsock)
> + return -ENOMEM;
>
> vqs = kmalloc_array(ARRAY_SIZE(vsock->vqs), sizeof(*vqs), GFP_KERNEL);
> if (!vqs) {
> diff --git a/mm/util.c b/mm/util.c
> index 7e0c240b5760..9306244b9f41 100644
> --- a/mm/util.c
> +++ b/mm/util.c
> @@ -333,7 +333,8 @@ EXPORT_SYMBOL(vm_mmap);
> * Uses kmalloc to get the memory but if the allocation fails then falls back
> * to the vmalloc allocator. Use kvfree for freeing the memory.
> *
> - * Reclaim modifiers - __GFP_NORETRY, __GFP_REPEAT and __GFP_NOFAIL are not supported
> + * Reclaim modifiers - __GFP_NORETRY and __GFP_NOFAIL are not supported. __GFP_REPEAT
> + * is supported only for large (>64kB) allocations
> */
> void *kvmalloc_node(size_t size, gfp_t flags, int node)
> {
> @@ -350,8 +351,18 @@ void *kvmalloc_node(size_t size, gfp_t flags, int node)
> * Make sure that larger requests are not too disruptive - no OOM
> * killer and no allocation failure warnings as we have a fallback
> */
> - if (size > PAGE_SIZE)
> - kmalloc_flags |= __GFP_NORETRY | __GFP_NOWARN;
> + if (size > PAGE_SIZE) {
> + kmalloc_flags |= __GFP_NOWARN;
> +
> + /*
> + * We have to override __GFP_REPEAT by __GFP_NORETRY for !costly
> + * requests because there is no other way to tell the allocator
> + * that we want to fail rather than retry endlessly.
> + */
> + if (!(kmalloc_flags & __GFP_REPEAT) ||
> + (size <= PAGE_SIZE << PAGE_ALLOC_COSTLY_ORDER))
> + kmalloc_flags |= __GFP_NORETRY;
> + }
>
> ret = kmalloc_node(size, kmalloc_flags, node);
>
> --
> 2.11.0
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