From: Michal Hocko mhocko@suse.com
Commit ce91f6ee5b3bbbad8caff61b1c46d845c8db19bf upstream.
kvmalloc warned about incompatible gfp_mask to catch abusers (mostly GFP_NOFS) with an intention that this will motivate authors of the code to fix those. Linus argues that this just motivates people to do even more hacks like
if (gfp == GFP_KERNEL) kvmalloc else kmalloc
I haven't seen this happening much (Linus pointed to bucket_lock special cases an atomic allocation but my git foo hasn't found much more) but it is true that we can grow those in future. Therefore Linus suggested to simply not fallback to vmalloc for incompatible gfp flags and rather stick with the kmalloc path.
Link: http://lkml.kernel.org/r/20180601115329.27807-1-mhocko@kernel.org Signed-off-by: Michal Hocko mhocko@suse.com Suggested-by: Linus Torvalds torvalds@linux-foundation.org Cc: Tom Herbert tom@quantonium.net Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Rishabh Bhatnagar risbhat@amazon.com --- Changelog: - Removed lib/bucket_locks.c diff as not present in 4.14
mm/util.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/mm/util.c b/mm/util.c index 84e775f5216f..7d80c8119dce 100644 --- a/mm/util.c +++ b/mm/util.c @@ -400,7 +400,8 @@ EXPORT_SYMBOL(vm_mmap); * __GFP_RETRY_MAYFAIL is supported, and it should be used only if kmalloc is * preferable to the vmalloc fallback, due to visible performance drawbacks. * - * Any use of gfp flags outside of GFP_KERNEL should be consulted with mm people. + * Please note that any use of gfp flags outside of GFP_KERNEL is careful to not + * fall back to vmalloc. */ void *kvmalloc_node(size_t size, gfp_t flags, int node) { @@ -411,7 +412,8 @@ void *kvmalloc_node(size_t size, gfp_t flags, int node) * vmalloc uses GFP_KERNEL for some internal allocations (e.g page tables) * so the given set of flags has to be compatible. */ - WARN_ON_ONCE((flags & GFP_KERNEL) != GFP_KERNEL); + if ((flags & GFP_KERNEL) != GFP_KERNEL) + return kmalloc_node(size, flags, node);
/* * We want to attempt a large physically contiguous block first because