On 01.11.2018 13:24, Michal Hocko wrote:
On Thu 01-11-18 13:09:16, Konstantin Khlebnikov wrote:
Allocations over KMALLOC_MAX_SIZE could be served only by vmalloc.
I would go on and say that allocations with sizes too large can actually
trigger a warning (once you have posted in the previous version outside
of the changelog area) because that might be interesting to people -
there are deployments to panic on warning and then a warning is much
more important.
It seems that warning isn't completely valid.
__alloc_pages_slowpath() handles this more gracefully:
/*
* In the slowpath, we sanity check order to avoid ever trying to
* reclaim >= MAX_ORDER areas which will never succeed. Callers may
* be using allocators in order of preference for an area that is
* too large.
*/
if (order >= MAX_ORDER) {
WARN_ON_ONCE(!(gfp_mask & __GFP_NOWARN));
return NULL;
}
Fast path is ready for order >= MAX_ORDER
Problem is in node_reclaim() which is called earlier than __alloc_pages_slowpath()
from surprising place - get_page_from_freelist()
Probably node_reclaim() simply needs something like this:
if (order >= MAX_ORDER)
return NODE_RECLAIM_NOSCAN;
Signed-off-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Thanks!
---
mm/util.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/mm/util.c b/mm/util.c
index 8bf08b5b5760..f5f04fa22814 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -392,6 +392,9 @@ void *kvmalloc_node(size_t size, gfp_t flags, int node)
gfp_t kmalloc_flags = flags;
void *ret;
+ if (size > KMALLOC_MAX_SIZE)
+ goto fallback;
+
/*
* vmalloc uses GFP_KERNEL for some internal allocations (e.g page tables)
* so the given set of flags has to be compatible.
@@ -422,6 +425,7 @@ void *kvmalloc_node(size_t size, gfp_t flags, int node)
if (ret || size <= PAGE_SIZE)
return ret;
+fallback:
return __vmalloc_node_flags_caller(size, node, flags,
__builtin_return_address(0));
}
