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Message-ID: <87tx89713l.fsf@rustcorp.com.au>
Date: Thu, 29 May 2014 12:17:10 +0930
From: Rusty Russell <rusty@...tcorp.com.au>
To: Minchan Kim <minchan@...nel.org>,
"Michael S. Tsirkin" <mst@...hat.com>
Cc: linux-kernel@...r.kernel.org,
Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...nel.org>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
Johannes Weiner <hannes@...xchg.org>,
Hugh Dickins <hughd@...gle.com>,
Dave Hansen <dave.hansen@...el.com>,
Steven Rostedt <rostedt@...dmis.org>,
"Linus Torvalds" <torvalds@...ux-foundation.org>
Subject: Re: [RFC 2/2] x86_64: expand kernel stack to 16K
Minchan Kim <minchan@...nel.org> writes:
> On Wed, May 28, 2014 at 12:04:09PM +0300, Michael S. Tsirkin wrote:
>> On Wed, May 28, 2014 at 03:53:59PM +0900, Minchan Kim wrote:
>> > [ 1065.604404] kworker/-5766 0d..2 1071625993us : stack_trace_call: 9) 6456 80 __kmalloc+0x1cb/0x200
>> > [ 1065.604404] kworker/-5766 0d..2 1071625993us : stack_trace_call: 10) 6376 376 vring_add_indirect+0x36/0x200
>> > [ 1065.604404] kworker/-5766 0d..2 1071625993us : stack_trace_call: 11) 6000 144 virtqueue_add_sgs+0x2e2/0x320
Hmm, we can actually skip the vring_add_indirect if we're hurting for
stack. It just means the request will try to fit linearly in the ring,
rather than using indirect.
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 1e443629f76d..496e727cefc8 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -184,6 +184,13 @@ static inline int vring_add_indirect(struct vring_virtqueue *vq,
return head;
}
+/* The Morton Technique */
+static noinline bool stack_trouble(void)
+{
+ unsigned long sp = (unsigned long)&sp;
+ return sp - (sp & ~(THREAD_SIZE - 1)) < 3000;
+}
+
static inline int virtqueue_add(struct virtqueue *_vq,
struct scatterlist *sgs[],
struct scatterlist *(*next)
@@ -226,7 +233,7 @@ static inline int virtqueue_add(struct virtqueue *_vq,
/* If the host supports indirect descriptor tables, and we have multiple
* buffers, then go indirect. FIXME: tune this threshold */
- if (vq->indirect && total_sg > 1 && vq->vq.num_free) {
+ if (vq->indirect && total_sg > 1 && vq->vq.num_free && !stack_trouble()) {
head = vring_add_indirect(vq, sgs, next, total_sg, total_out,
total_in,
out_sgs, in_sgs, gfp);
--
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