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Subject[PATCH] mm: support __GFP_REPEAT in kvmalloc_node
While checking opencoded users I've encountered that vhost code would
really like to use kvmalloc with __GFP_REPEAT [1] so the following patch
adds support for __GFP_REPEAT and converts both vhost users.

So currently I am sitting on 3 patches. I will wait for more feedback -
especially about potential split ups or cleanups few more days and then
repost the whole series.

[1] http://lkml.kernel.org/r/20170104150800.GO25453@dhcp22.suse.cz
---
From 0b92e4d2e040524b878d4e7b9ee88fbad5284b33 Mon Sep 17 00:00:00 2001
From: Michal Hocko <mhocko@suse.com>
Date: Wed, 4 Jan 2017 18:01:39 +0100
Subject: [PATCH] mm: support __GFP_REPEAT in kvmalloc_node

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.
"

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.

This patch shouldn't introduce any functional change.

Cc: "Michael S. Tsirkin" <mst@redhat.com>
Signed-off-by: Michal Hocko <mhocko@suse.com>
---
drivers/vhost/net.c | 9 +++------
drivers/vhost/vsock.c | 9 +++------
mm/util.c | 9 +++++++--
3 files changed, 13 insertions(+), 14 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/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 8e4ea6cbe379..a2bfb85e60e5 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -348,8 +348,13 @@ 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;
+
+ 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
--
Michal Hocko
SUSE Labs

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