答复: [PATCH][net-next] vhost:net: allocate 32KB memory instead of 32K pages when page frag refill

2018-11-22 Thread Li,Rongqing 

On 2018/11/23 上午10:04, Li RongQing wrote:
> >when page frag refills, 32K pages, 128MB memory is asked, it hardly 
> >successes when system has memory stress


> Looking at get_order(), it seems we get 3 after get_order(32768) since it 
> accepts the size of block.

You are right, I understood wrongly, 

Please drop this patch, sorry for the noise

-Q

Re: [PATCH][net-next] vhost:net: allocate 32KB memory instead of 32K pages when page frag refill

2018-11-22 Thread Jason Wang 



On 2018/11/23 上午10:04, Li RongQing wrote:

when page frag refills, 32K pages, 128MB memory is asked, it
hardly successes when system has memory stress



Looking at get_order(), it seems we get 3 after get_order(32768) since 
it accepts the size of block.


/**
 * get_order - Determine the allocation order of a memory size
 * @size: The size for which to get the order
...

define get_order(n)    \
(   \
    __builtin_constant_p(n) ? ( \
    ((n) == 0UL) ? BITS_PER_LONG - PAGE_SHIFT : \
    (((n) < (1UL << PAGE_SHIFT)) ? 0 :  \
 ilog2((n) - 1) - PAGE_SHIFT + 1)   \

  ^^^

    ) : \
    __get_order(n)  \
)




And such large memory size will cause the underflow of reference
bias, and make refcount of page chaos, since reference bias will
be decreased to negative before the allocated memory is used up



Do you have reproducer for this issue?

Thanks




so 32KB memory is safe choice, meanwhile, remove a unnecessary
check

Fixes: e4dab1e6ea64 ("vhost_net: mitigate page reference counting during page frag 
refill")
Signed-off-by: Zhang Yu 
Signed-off-by: Li RongQing 
---
  drivers/vhost/net.c | 22 +++---
  1 file changed, 11 insertions(+), 11 deletions(-)

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index d919284f103b..b933a4a8e4ba 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -641,7 +641,7 @@ static bool tx_can_batch(struct vhost_virtqueue *vq, size_t 
total_len)
   !vhost_vq_avail_empty(vq->dev, vq);
  }
  
-#define SKB_FRAG_PAGE_ORDER get_order(32768)

+#define SKB_FRAG_PAGE_ORDER3
  
  static bool vhost_net_page_frag_refill(struct vhost_net *net, unsigned int sz,

   struct page_frag *pfrag, gfp_t gfp)
@@ -654,17 +654,17 @@ static bool vhost_net_page_frag_refill(struct vhost_net 
*net, unsigned int sz,
  
  	pfrag->offset = 0;

net->refcnt_bias = 0;
-   if (SKB_FRAG_PAGE_ORDER) {
-   /* Avoid direct reclaim but allow kswapd to wake */
-   pfrag->page = alloc_pages((gfp & ~__GFP_DIRECT_RECLAIM) |
- __GFP_COMP | __GFP_NOWARN |
- __GFP_NORETRY,
- SKB_FRAG_PAGE_ORDER);
-   if (likely(pfrag->page)) {
-   pfrag->size = PAGE_SIZE << SKB_FRAG_PAGE_ORDER;
-   goto done;
-   }
+
+   /* Avoid direct reclaim but allow kswapd to wake */
+   pfrag->page = alloc_pages((gfp & ~__GFP_DIRECT_RECLAIM) |
+ __GFP_COMP | __GFP_NOWARN |
+ __GFP_NORETRY,
+ SKB_FRAG_PAGE_ORDER);
+   if (likely(pfrag->page)) {
+   pfrag->size = PAGE_SIZE << SKB_FRAG_PAGE_ORDER;
+   goto done;
}
+
pfrag->page = alloc_page(gfp);
if (likely(pfrag->page)) {
pfrag->size = PAGE_SIZE;

[PATCH][net-next] vhost:net: allocate 32KB memory instead of 32K pages when page frag refill

2018-11-22 Thread Li RongQing 
when page frag refills, 32K pages, 128MB memory is asked, it
hardly successes when system has memory stress

And such large memory size will cause the underflow of reference
bias, and make refcount of page chaos, since reference bias will
be decreased to negative before the allocated memory is used up

so 32KB memory is safe choice, meanwhile, remove a unnecessary
check

Fixes: e4dab1e6ea64 ("vhost_net: mitigate page reference counting during page 
frag refill")
Signed-off-by: Zhang Yu 
Signed-off-by: Li RongQing 
---
 drivers/vhost/net.c | 22 +++---
 1 file changed, 11 insertions(+), 11 deletions(-)

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index d919284f103b..b933a4a8e4ba 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -641,7 +641,7 @@ static bool tx_can_batch(struct vhost_virtqueue *vq, size_t 
total_len)
   !vhost_vq_avail_empty(vq->dev, vq);
 }
 
-#define SKB_FRAG_PAGE_ORDER get_order(32768)
+#define SKB_FRAG_PAGE_ORDER3
 
 static bool vhost_net_page_frag_refill(struct vhost_net *net, unsigned int sz,
   struct page_frag *pfrag, gfp_t gfp)
@@ -654,17 +654,17 @@ static bool vhost_net_page_frag_refill(struct vhost_net 
*net, unsigned int sz,
 
pfrag->offset = 0;
net->refcnt_bias = 0;
-   if (SKB_FRAG_PAGE_ORDER) {
-   /* Avoid direct reclaim but allow kswapd to wake */
-   pfrag->page = alloc_pages((gfp & ~__GFP_DIRECT_RECLAIM) |
- __GFP_COMP | __GFP_NOWARN |
- __GFP_NORETRY,
- SKB_FRAG_PAGE_ORDER);
-   if (likely(pfrag->page)) {
-   pfrag->size = PAGE_SIZE << SKB_FRAG_PAGE_ORDER;
-   goto done;
-   }
+
+   /* Avoid direct reclaim but allow kswapd to wake */
+   pfrag->page = alloc_pages((gfp & ~__GFP_DIRECT_RECLAIM) |
+ __GFP_COMP | __GFP_NOWARN |
+ __GFP_NORETRY,
+ SKB_FRAG_PAGE_ORDER);
+   if (likely(pfrag->page)) {
+   pfrag->size = PAGE_SIZE << SKB_FRAG_PAGE_ORDER;
+   goto done;
}
+
pfrag->page = alloc_page(gfp);
if (likely(pfrag->page)) {
pfrag->size = PAGE_SIZE;
-- 
2.16.2