Re: [PATCH 2] mm/kvmalloc: do not call kmalloc for size > KMALLOC_MAX_SIZE

[Konstantin Khlebnikov]

On 05.11.2018 16:03, Vlastimil Babka wrote:

On 11/1/18 11:09 AM, Konstantin Khlebnikov wrote:

Allocations over KMALLOC_MAX_SIZE could be served only by vmalloc.

Signed-off-by: Konstantin Khlebnikov <khlebni...@yandex-team.ru>

Makes sense regardless of warnings stuff.

Acked-by: Vlastimil Babka <vba...@suse.cz>

But it must be moved below the GFP_KERNEL check!

But kmalloc cannot handle it regardless of GFP.

Ok maybe write something like this

if (size > KMALLOC_MAX_SIZE) {
        if (WARN_ON_ONCE((flags & GFP_KERNEL) != GFP_KERNEL)
                return NULL;
        goto do_vmalloc;
}

or fix that uncertainty right in vmalloc

For now comment in vmalloc declares

 *      Any use of gfp flags outside of GFP_KERNEL should be consulted
 *      with mm people.

=)

---
  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));
  }