On Thu, Jun 11, 2015 at 03:53:04PM -0700, Eric Dumazet wrote:
> On Thu, 2015-06-11 at 15:27 -0700, Shaohua Li wrote:
> > We saw excessive direct memory compaction triggered by skb_page_frag_refill.
> > This causes performance issues and add latency. Commit 5640f7685831e0
> > introduces the order-3 allocation. According to the changelog, the order-3
> > allocation isn't a must-have but to improve performance. But direct memory
> > compaction has high overhead. The benefit of order-3 allocation can't
> > compensate the overhead of direct memory compaction.
> >
> > This patch makes the order-3 page allocation atomic. If there is no memory
> > pressure and memory isn't fragmented, the alloction will still success, so we
> > don't sacrifice the order-3 benefit here. If the atomic allocation fails,
> > direct memory compaction will not be triggered, skb_page_frag_refill will
> > fallback to order-0 immediately, hence the direct memory compaction overhead is
> > avoided. In the allocation failure case, kswapd is waken up and doing
> > compaction, so chances are allocation could success next time.
> >
> > The mellanox driver does similar thing, if this is accepted, we must fix
> > the driver too.
> >
> > V2: make the changelog clearer
> >
> > Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
> > Signed-off-by: Shaohua Li <shli@xxxxxx>
> > ---
> > net/core/sock.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/net/core/sock.c b/net/core/sock.c
> > index 292f422..e9855a4 100644
> > --- a/net/core/sock.c
> > +++ b/net/core/sock.c
> > @@ -1883,7 +1883,7 @@ bool skb_page_frag_refill(unsigned int sz, struct page_frag *pfrag, gfp_t gfp)
> >
> > pfrag->offset = 0;
> > if (SKB_FRAG_PAGE_ORDER) {
> > - pfrag->page = alloc_pages(gfp | __GFP_COMP |
> > + pfrag->page = alloc_pages((gfp & ~__GFP_WAIT) | __GFP_COMP |
> > __GFP_NOWARN | __GFP_NORETRY,
> > SKB_FRAG_PAGE_ORDER);
> > if (likely(pfrag->page)) {
>
>
> OK, now what about alloc_skb_with_frags() ?
>
> This should have same problem right ?
Ok, looks similar, added. Didn't trigger this one though.
>From 940dde18f7f655377a4c30d5de54c9eff15ab5a5 Mon Sep 17 00:00:00 2001
Message-Id: <940dde18f7f655377a4c30d5de54c9eff15ab5a5.1434065353.git.shli@xxxxxx>
From: Shaohua Li <shli@xxxxxx>
Date: Thu, 11 Jun 2015 16:16:21 -0700
Subject: [RFC] net: use atomic allocation for order-3 page allocation
We saw excessive direct memory compaction triggered by skb_page_frag_refill.
This causes performance issues and add latency. Commit 5640f7685831e0
introduces the order-3 allocation. According to the changelog, the order-3
allocation isn't a must-have but to improve performance. But direct memory
compaction has high overhead. The benefit of order-3 allocation can't
compensate the overhead of direct memory compaction.
This patch makes the order-3 page allocation atomic. If there is no memory
pressure and memory isn't fragmented, the alloction will still success, so we
don't sacrifice the order-3 benefit here. If the atomic allocation fails,
direct memory compaction will not be triggered, skb_page_frag_refill will
fallback to order-0 immediately, hence the direct memory compaction overhead is
avoided. In the allocation failure case, kswapd is waken up and doing
compaction, so chances are allocation could success next time.
alloc_skb_with_frags is the same.
The mellanox driver does similar thing, if this is accepted, we must fix
the driver too.
V3: fix the same issue in alloc_skb_with_frags as pointed out by Eric
V2: make the changelog clearer
Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
Cc: Chris Mason <clm@xxxxxx>
Cc: Debabrata Banerjee <dbavatar@xxxxxxxxx>
Signed-off-by: Shaohua Li <shli@xxxxxx>
---
net/core/skbuff.c | 4 +++-
net/core/sock.c | 2 +-
2 files changed, 4 insertions(+), 2 deletions(-)
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 3cfff2a..9856c7a 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -4398,7 +4398,9 @@ struct sk_buff *alloc_skb_with_frags(unsigned long header_len,
while (order) {
if (npages >= 1 << order) {
- page = alloc_pages(gfp_mask |
+ gfp_t gfp = order > 0 ?
+ gfp_mask & ~__GFP_WAIT : gfp_mask;
+ page = alloc_pages(gfp |
__GFP_COMP |
__GFP_NOWARN |
__GFP_NORETRY,
diff --git a/net/core/sock.c b/net/core/sock.c
index 292f422..e9855a4 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1883,7 +1883,7 @@ bool skb_page_frag_refill(unsigned int sz, struct page_frag *pfrag, gfp_t gfp)
pfrag->offset = 0;
if (SKB_FRAG_PAGE_ORDER) {
- pfrag->page = alloc_pages(gfp | __GFP_COMP |
+ pfrag->page = alloc_pages((gfp & ~__GFP_WAIT) | __GFP_COMP |
__GFP_NOWARN | __GFP_NORETRY,
SKB_FRAG_PAGE_ORDER);
if (likely(pfrag->page)) {
--
1.8.1
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