diff mbox series

[net-next,v4,2/5] page_frag: unify gfp bits for order 3 page allocation

Message ID 20240130113710.34511-3-linyunsheng@huawei.com (mailing list archive)
State New
Headers show
Series [net-next,v4,1/5] mm/page_alloc: modify page_frag_alloc_align() to accept align as an argument | expand

Commit Message

Yunsheng Lin Jan. 30, 2024, 11:37 a.m. UTC 
Currently there seems to be three page frag implementions
which all try to allocate order 3 page, if that fails, it
then fail back to allocate order 0 page, and each of them
all allow order 3 page allocation to fail under certain
condition by using specific gfp bits.

The gfp bits for order 3 page allocation are different
between different implementation, __GFP_NOMEMALLOC is
or'd to forbid access to emergency reserves memory for
__page_frag_cache_refill(), but it is not or'd in other
implementions, __GFP_DIRECT_RECLAIM is masked off to avoid
direct reclaim in skb_page_frag_refill(), but it is not
masked off in __page_frag_cache_refill().

This patch unifies the gfp bits used between different
implementions by or'ing __GFP_NOMEMALLOC and masking off
__GFP_DIRECT_RECLAIM for order 3 page allocation to avoid
possible pressure for mm.

Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
Reviewed-by: Alexander Duyck <alexanderduyck@fb.com>
CC: Alexander Duyck <alexander.duyck@gmail.com>
---
 drivers/vhost/net.c | 2 +-
 mm/page_alloc.c     | 4 ++--
 net/core/sock.c     | 2 +-
 3 files changed, 4 insertions(+), 4 deletions(-)

Comments

Paolo Abeni Feb. 1, 2024, 1:16 p.m. UTC | #1 
On Tue, 2024-01-30 at 19:37 +0800, Yunsheng Lin wrote:
> Currently there seems to be three page frag implementions
> which all try to allocate order 3 page, if that fails, it
> then fail back to allocate order 0 page, and each of them
> all allow order 3 page allocation to fail under certain
> condition by using specific gfp bits.
> 
> The gfp bits for order 3 page allocation are different
> between different implementation, __GFP_NOMEMALLOC is
> or'd to forbid access to emergency reserves memory for
> __page_frag_cache_refill(), but it is not or'd in other
> implementions, __GFP_DIRECT_RECLAIM is masked off to avoid
> direct reclaim in skb_page_frag_refill(), but it is not
> masked off in __page_frag_cache_refill().
> 
> This patch unifies the gfp bits used between different
> implementions by or'ing __GFP_NOMEMALLOC and masking off
> __GFP_DIRECT_RECLAIM for order 3 page allocation to avoid
> possible pressure for mm.
> 
> Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
> Reviewed-by: Alexander Duyck <alexanderduyck@fb.com>
> CC: Alexander Duyck <alexander.duyck@gmail.com>
> ---
>  drivers/vhost/net.c | 2 +-
>  mm/page_alloc.c     | 4 ++--
>  net/core/sock.c     | 2 +-
>  3 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index f2ed7167c848..e574e21cc0ca 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -670,7 +670,7 @@ static bool vhost_net_page_frag_refill(struct vhost_net *net, unsigned int sz,
>  		/* Avoid direct reclaim but allow kswapd to wake */
>  		pfrag->page = alloc_pages((gfp & ~__GFP_DIRECT_RECLAIM) |
>  					  __GFP_COMP | __GFP_NOWARN |
> -					  __GFP_NORETRY,
> +					  __GFP_NORETRY | __GFP_NOMEMALLOC,
>  					  SKB_FRAG_PAGE_ORDER);

>  		if (likely(pfrag->page)) {
>  			pfrag->size = PAGE_SIZE << SKB_FRAG_PAGE_ORDER;
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index c0f7e67c4250..636145c29f70 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -4685,8 +4685,8 @@ static struct page *__page_frag_cache_refill(struct page_frag_cache *nc,
>  	gfp_t gfp = gfp_mask;
>  
>  #if (PAGE_SIZE < PAGE_FRAG_CACHE_MAX_SIZE)
> -	gfp_mask |= __GFP_COMP | __GFP_NOWARN | __GFP_NORETRY |
> -		    __GFP_NOMEMALLOC;
> +	gfp_mask = (gfp_mask & ~__GFP_DIRECT_RECLAIM) |  __GFP_COMP |
> +		   __GFP_NOWARN | __GFP_NORETRY | __GFP_NOMEMALLOC;
>  	page = alloc_pages_node(NUMA_NO_NODE, gfp_mask,
>  				PAGE_FRAG_CACHE_MAX_ORDER);
>  	nc->size = page ? PAGE_FRAG_CACHE_MAX_SIZE : PAGE_SIZE;
> diff --git a/net/core/sock.c b/net/core/sock.c
> index 88bf810394a5..8289a3d8c375 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -2919,7 +2919,7 @@ bool skb_page_frag_refill(unsigned int sz, struct page_frag *pfrag, gfp_t gfp)
>  		/* Avoid direct reclaim but allow kswapd to wake */
>  		pfrag->page = alloc_pages((gfp & ~__GFP_DIRECT_RECLAIM) |
>  					  __GFP_COMP | __GFP_NOWARN |
> -					  __GFP_NORETRY,
> +					  __GFP_NORETRY | __GFP_NOMEMALLOC,
>  					  SKB_FRAG_PAGE_ORDER);

This will prevent memory reserve usage when allocating order 3 pages,
but not when allocating a single page as a fallback. Still different
from the __page_frag_cache_refill() allocator - which never accesses
the memory reserves.

I'm unsure we want to propagate the __page_frag_cache_refill behavior
here, the current behavior could be required by some systems.

It looks like this series still leave the skb_page_frag_refill()
allocator alone, what about dropping this chunk, too? 

Thanks!

Paolo
Yunsheng Lin Feb. 2, 2024, 2:10 a.m. UTC | #2 
On 2024/2/1 21:16, Paolo Abeni wrote:
> On Tue, 2024-01-30 at 19:37 +0800, Yunsheng Lin wrote:
>> Currently there seems to be three page frag implementions
>> which all try to allocate order 3 page, if that fails, it
>> then fail back to allocate order 0 page, and each of them
>> all allow order 3 page allocation to fail under certain
>> condition by using specific gfp bits.
>>
>> The gfp bits for order 3 page allocation are different
>> between different implementation, __GFP_NOMEMALLOC is
>> or'd to forbid access to emergency reserves memory for
>> __page_frag_cache_refill(), but it is not or'd in other
>> implementions, __GFP_DIRECT_RECLAIM is masked off to avoid
>> direct reclaim in skb_page_frag_refill(), but it is not
>> masked off in __page_frag_cache_refill().
>>
>> This patch unifies the gfp bits used between different
>> implementions by or'ing __GFP_NOMEMALLOC and masking off
>> __GFP_DIRECT_RECLAIM for order 3 page allocation to avoid
>> possible pressure for mm.
>>
>> Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
>> Reviewed-by: Alexander Duyck <alexanderduyck@fb.com>
>> CC: Alexander Duyck <alexander.duyck@gmail.com>
>> ---
>>  drivers/vhost/net.c | 2 +-
>>  mm/page_alloc.c     | 4 ++--
>>  net/core/sock.c     | 2 +-
>>  3 files changed, 4 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
>> index f2ed7167c848..e574e21cc0ca 100644
>> --- a/drivers/vhost/net.c
>> +++ b/drivers/vhost/net.c
>> @@ -670,7 +670,7 @@ static bool vhost_net_page_frag_refill(struct vhost_net *net, unsigned int sz,
>>  		/* Avoid direct reclaim but allow kswapd to wake */
>>  		pfrag->page = alloc_pages((gfp & ~__GFP_DIRECT_RECLAIM) |
>>  					  __GFP_COMP | __GFP_NOWARN |
>> -					  __GFP_NORETRY,
>> +					  __GFP_NORETRY | __GFP_NOMEMALLOC,
>>  					  SKB_FRAG_PAGE_ORDER);
> 
>>  		if (likely(pfrag->page)) {
>>  			pfrag->size = PAGE_SIZE << SKB_FRAG_PAGE_ORDER;
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index c0f7e67c4250..636145c29f70 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -4685,8 +4685,8 @@ static struct page *__page_frag_cache_refill(struct page_frag_cache *nc,
>>  	gfp_t gfp = gfp_mask;
>>  
>>  #if (PAGE_SIZE < PAGE_FRAG_CACHE_MAX_SIZE)
>> -	gfp_mask |= __GFP_COMP | __GFP_NOWARN | __GFP_NORETRY |
>> -		    __GFP_NOMEMALLOC;
>> +	gfp_mask = (gfp_mask & ~__GFP_DIRECT_RECLAIM) |  __GFP_COMP |
>> +		   __GFP_NOWARN | __GFP_NORETRY | __GFP_NOMEMALLOC;
>>  	page = alloc_pages_node(NUMA_NO_NODE, gfp_mask,
>>  				PAGE_FRAG_CACHE_MAX_ORDER);
>>  	nc->size = page ? PAGE_FRAG_CACHE_MAX_SIZE : PAGE_SIZE;
>> diff --git a/net/core/sock.c b/net/core/sock.c
>> index 88bf810394a5..8289a3d8c375 100644
>> --- a/net/core/sock.c
>> +++ b/net/core/sock.c
>> @@ -2919,7 +2919,7 @@ bool skb_page_frag_refill(unsigned int sz, struct page_frag *pfrag, gfp_t gfp)
>>  		/* Avoid direct reclaim but allow kswapd to wake */
>>  		pfrag->page = alloc_pages((gfp & ~__GFP_DIRECT_RECLAIM) |
>>  					  __GFP_COMP | __GFP_NOWARN |
>> -					  __GFP_NORETRY,
>> +					  __GFP_NORETRY | __GFP_NOMEMALLOC,
>>  					  SKB_FRAG_PAGE_ORDER);
> 
> This will prevent memory reserve usage when allocating order 3 pages,
> but not when allocating a single page as a fallback. Still different

More accurately, the above ensures memory reserve is always not used
for order 3 pages, whether memory reserve is used for order 0 pages
depending on original 'gfp' flags, if 'gfp' does not have __GFP_NOMEMALLOC
bit set, memory reserve may still be used  for order 0 pages.

> from the __page_frag_cache_refill() allocator - which never accesses
> the memory reserves.

I am not really sure I understand the above commemt.
The semantic is the same as skb_page_frag_refill() as explained above
as my understanding. Note that __page_frag_cache_refill() use 'gfp_mask'
for allocating order 3 pages and use the original 'gfp' for allocating
order 0 pages.

> 
> I'm unsure we want to propagate the __page_frag_cache_refill behavior
> here, the current behavior could be required by some systems.
> 
> It looks like this series still leave the skb_page_frag_refill()
> allocator alone, what about dropping this chunk, too? 

As explained above, I would prefer to keep it as it is as it seems
to be quite obvious that we can avoid possible pressure for mm by
not using memory reserve for order 3 pages as we have the fallback
for order 0 pages.

Please let me know if there is anything obvious I missed.

> 
> Thanks!
> 
> Paolo
> 
> 
> .
>
Paolo Abeni Feb. 2, 2024, 8:36 a.m. UTC | #3 
On Fri, 2024-02-02 at 10:10 +0800, Yunsheng Lin wrote:
> On 2024/2/1 21:16, Paolo Abeni wrote:
> 
> > from the __page_frag_cache_refill() allocator - which never accesses
> > the memory reserves.
> 
> I am not really sure I understand the above commemt.
> The semantic is the same as skb_page_frag_refill() as explained above
> as my understanding. Note that __page_frag_cache_refill() use 'gfp_mask'
> for allocating order 3 pages and use the original 'gfp' for allocating
> order 0 pages.

You are right! I got fooled misreading 'gfp' as 'gfp_mask' in there.

> > I'm unsure we want to propagate the __page_frag_cache_refill behavior
> > here, the current behavior could be required by some systems.
> > 
> > It looks like this series still leave the skb_page_frag_refill()
> > allocator alone, what about dropping this chunk, too? 
> 
> As explained above, I would prefer to keep it as it is as it seems
> to be quite obvious that we can avoid possible pressure for mm by
> not using memory reserve for order 3 pages as we have the fallback
> for order 0 pages.
> 
> Please let me know if there is anything obvious I missed.
> 

I still think/fear that behaviours changes here could have
subtle/negative side effects - even if I agree the change looks safe.

I think the series without this patch would still achieve its goals and
would be much more uncontroversial. What about move this patch as a
standalone follow-up?

Thanks!

Paolo
Yunsheng Lin Feb. 2, 2024, 12:26 p.m. UTC | #4 
On 2024/2/2 16:36, Paolo Abeni wrote:
> On Fri, 2024-02-02 at 10:10 +0800, Yunsheng Lin wrote:
>> On 2024/2/1 21:16, Paolo Abeni wrote:
>>
>>> from the __page_frag_cache_refill() allocator - which never accesses
>>> the memory reserves.
>>
>> I am not really sure I understand the above commemt.
>> The semantic is the same as skb_page_frag_refill() as explained above
>> as my understanding. Note that __page_frag_cache_refill() use 'gfp_mask'
>> for allocating order 3 pages and use the original 'gfp' for allocating
>> order 0 pages.
> 
> You are right! I got fooled misreading 'gfp' as 'gfp_mask' in there.
> 
>>> I'm unsure we want to propagate the __page_frag_cache_refill behavior
>>> here, the current behavior could be required by some systems.
>>>
>>> It looks like this series still leave the skb_page_frag_refill()
>>> allocator alone, what about dropping this chunk, too? 
>>
>> As explained above, I would prefer to keep it as it is as it seems
>> to be quite obvious that we can avoid possible pressure for mm by
>> not using memory reserve for order 3 pages as we have the fallback
>> for order 0 pages.
>>
>> Please let me know if there is anything obvious I missed.
>>
> 
> I still think/fear that behaviours changes here could have
> subtle/negative side effects - even if I agree the change looks safe.
> 
> I think the series without this patch would still achieve its goals and
> would be much more uncontroversial. What about move this patch as a
> standalone follow-up?

Fair enough, will remove that for now.

> 
> Thanks!
> 
> Paolo
> 
> .
>
diff mbox series

Patch

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index f2ed7167c848..e574e21cc0ca 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -670,7 +670,7 @@  static bool vhost_net_page_frag_refill(struct vhost_net *net, unsigned int sz,
 		/* Avoid direct reclaim but allow kswapd to wake */
 		pfrag->page = alloc_pages((gfp & ~__GFP_DIRECT_RECLAIM) |
 					  __GFP_COMP | __GFP_NOWARN |
-					  __GFP_NORETRY,
+					  __GFP_NORETRY | __GFP_NOMEMALLOC,
 					  SKB_FRAG_PAGE_ORDER);
 		if (likely(pfrag->page)) {
 			pfrag->size = PAGE_SIZE << SKB_FRAG_PAGE_ORDER;
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index c0f7e67c4250..636145c29f70 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4685,8 +4685,8 @@  static struct page *__page_frag_cache_refill(struct page_frag_cache *nc,
 	gfp_t gfp = gfp_mask;
 
 #if (PAGE_SIZE < PAGE_FRAG_CACHE_MAX_SIZE)
-	gfp_mask |= __GFP_COMP | __GFP_NOWARN | __GFP_NORETRY |
-		    __GFP_NOMEMALLOC;
+	gfp_mask = (gfp_mask & ~__GFP_DIRECT_RECLAIM) |  __GFP_COMP |
+		   __GFP_NOWARN | __GFP_NORETRY | __GFP_NOMEMALLOC;
 	page = alloc_pages_node(NUMA_NO_NODE, gfp_mask,
 				PAGE_FRAG_CACHE_MAX_ORDER);
 	nc->size = page ? PAGE_FRAG_CACHE_MAX_SIZE : PAGE_SIZE;
diff --git a/net/core/sock.c b/net/core/sock.c
index 88bf810394a5..8289a3d8c375 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -2919,7 +2919,7 @@  bool skb_page_frag_refill(unsigned int sz, struct page_frag *pfrag, gfp_t gfp)
 		/* Avoid direct reclaim but allow kswapd to wake */
 		pfrag->page = alloc_pages((gfp & ~__GFP_DIRECT_RECLAIM) |
 					  __GFP_COMP | __GFP_NOWARN |
-					  __GFP_NORETRY,
+					  __GFP_NORETRY | __GFP_NOMEMALLOC,
 					  SKB_FRAG_PAGE_ORDER);
 		if (likely(pfrag->page)) {
 			pfrag->size = PAGE_SIZE << SKB_FRAG_PAGE_ORDER;