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);
if (likely(pfrag->page)) {
pfrag->size = PAGE_SIZE << SKB_FRAG_PAGE_ORDER;
--
2.33.0On 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
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
>
>
> .
>
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
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 > > . >
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