From: Vlastimil Babka <vbabka@suse.cz>
To: Shaohua Li <shli@fb.com>, netdev@vger.kernel.org
Cc: davem@davemloft.net, Kernel-team@fb.com, clm@fb.com,
linux-mm@kvack.org, dbavatar@gmail.com,
Eric Dumazet <edumazet@google.com>
Subject: Re: [RFC V3] net: don't wait for order-3 page allocation
Date: Fri, 12 Jun 2015 11:36:52 +0200 [thread overview]
Message-ID: <557AA834.8070503@suse.cz> (raw)
In-Reply-To: <0099265406c32b9b9057de100404a4148d602cdd.1434066549.git.shli@fb.com>
On 06/12/2015 01:50 AM, 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.
>
> 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@google.com>
> Cc: Chris Mason <clm@fb.com>
> Cc: Debabrata Banerjee <dbavatar@gmail.com>
> Signed-off-by: Shaohua Li <shli@fb.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
> ---
> net/core/skbuff.c | 2 +-
> net/core/sock.c | 2 +-
> 2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 3cfff2a..41ec022 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -4398,7 +4398,7 @@ struct sk_buff *alloc_skb_with_frags(unsigned long header_len,
>
> while (order) {
> if (npages >= 1 << order) {
> - page = alloc_pages(gfp_mask |
> + page = alloc_pages((gfp_mask & ~__GFP_WAIT) |
> __GFP_COMP |
> __GFP_NOWARN |
> __GFP_NORETRY,
Note that __GFP_NORETRY is weaker than ~__GFP_WAIT and thus redundant.
But it won't hurt anything leaving it there. And you might consider
__GFP_NO_KSWAPD instead, as I said in the other thread.
> 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)) {
>
--
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WARNING: multiple messages have this Message-ID (diff)
From: Vlastimil Babka <vbabka@suse.cz>
To: Shaohua Li <shli@fb.com>, netdev@vger.kernel.org
Cc: davem@davemloft.net, Kernel-team@fb.com, clm@fb.com,
linux-mm@kvack.org, dbavatar@gmail.com,
Eric Dumazet <edumazet@google.com>
Subject: Re: [RFC V3] net: don't wait for order-3 page allocation
Date: Fri, 12 Jun 2015 11:36:52 +0200 [thread overview]
Message-ID: <557AA834.8070503@suse.cz> (raw)
In-Reply-To: <0099265406c32b9b9057de100404a4148d602cdd.1434066549.git.shli@fb.com>
On 06/12/2015 01:50 AM, 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.
>
> 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@google.com>
> Cc: Chris Mason <clm@fb.com>
> Cc: Debabrata Banerjee <dbavatar@gmail.com>
> Signed-off-by: Shaohua Li <shli@fb.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
> ---
> net/core/skbuff.c | 2 +-
> net/core/sock.c | 2 +-
> 2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 3cfff2a..41ec022 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -4398,7 +4398,7 @@ struct sk_buff *alloc_skb_with_frags(unsigned long header_len,
>
> while (order) {
> if (npages >= 1 << order) {
> - page = alloc_pages(gfp_mask |
> + page = alloc_pages((gfp_mask & ~__GFP_WAIT) |
> __GFP_COMP |
> __GFP_NOWARN |
> __GFP_NORETRY,
Note that __GFP_NORETRY is weaker than ~__GFP_WAIT and thus redundant.
But it won't hurt anything leaving it there. And you might consider
__GFP_NO_KSWAPD instead, as I said in the other thread.
> 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)) {
>
next prev parent reply other threads:[~2015-06-12 9:36 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-11 23:50 [RFC V3] net: don't wait for order-3 page allocation Shaohua Li
2015-06-11 23:50 ` Shaohua Li
2015-06-12 0:02 ` Eric Dumazet
2015-06-12 0:02 ` Eric Dumazet
2015-06-12 0:34 ` David Miller
2015-06-12 0:34 ` David Miller
2015-06-12 9:36 ` Vlastimil Babka [this message]
2015-06-12 9:36 ` Vlastimil Babka
2015-06-17 23:02 ` David Rientjes
2015-06-17 23:02 ` David Rientjes
2015-06-18 14:30 ` Michal Hocko
2015-06-18 14:30 ` Michal Hocko
2015-06-18 14:35 ` Eric Dumazet
2015-06-18 14:43 ` Michal Hocko
2015-06-18 14:43 ` Michal Hocko
2015-06-18 15:22 ` Vlastimil Babka
2015-06-18 15:47 ` Michal Hocko
2015-06-18 15:47 ` Michal Hocko
2015-06-30 23:49 ` David Rientjes
2015-06-30 23:49 ` David Rientjes
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