On 5 Jan 2019, at 7:46, Jesper Dangaard Brouer wrote:
On Thu, 20 Dec 2018 14:21:32 -0800
Jonathan Lemon <[email protected]> wrote:
Return pfmemalloc pages back to the page allocator, instead of
holding them
in the page pool.
Signed-off-by: Jonathan Lemon <[email protected]>
---
net/core/page_pool.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index 43a932cb609b..364b893be66f 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -233,7 +233,7 @@ void __page_pool_put_page(struct page_pool *pool,
*
* refcnt == 1 means page_pool owns page, and can recycle it.
*/
- if (likely(page_ref_count(page) == 1)) {
+ if (likely(page_ref_count(page) == 1 && !page_is_pfmemalloc(page)))
{
I took at closer look at the page_pool issue recycling pages from
emergency reserve (pfmemalloc), and it actually cannot happen, because
page_pool does not use the __GFP_MEMALLOC gfp_t flag. Thus, page_pool
are not allowed to get pages from the emergency reserve in the first
place (unless ksoftirqd current->flags have PF_MEMALLOC, which I don't
think it have).
page_pool_dev_alloc_pages() sets GFP_ATOMIC | __GFP_NOWARN. If the
page pool really doesn't want to allow emergency reserves, then
shouldn't
it set __GFP_NOMEMALLOC as well?
See: page_pool_dev_alloc_pages() compared to __dev_alloc_pages().
The doc for:
/* %__GFP_MEMALLOC allows access to all memory. This should only be
used when
* the caller guarantees the allocation will allow more memory to be
freed
* very shortly e.g. process exiting or swapping. Users either should
* be the MM or co-ordinating closely with the VM (e.g. swap over
NFS).
*/
With that desc, I don't understand why we actually allow
dev_alloc_pages()
to get emergency reserve (pfmemalloc) pages, as we store these in an
RX-ring queue (usual size 512-1024) that isn't used until N-packets
later... even if used as a signal to network stack, to free other
resources, this happens at a later point-in-time, not "very shortly".
--
Best regards,
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat
LinkedIn: http://www.linkedin.com/in/brouer
