Messages in this thread | | | Subject | Re: [PATCH 2/2] ipc: use kmalloc for msg_queue and shmid_kernel | From | Vasily Averin <> | Date | Wed, 28 Apr 2021 08:15:10 +0300 |
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On 4/26/21 1:25 PM, Michal Hocko wrote: > Using kvmalloc for sub page size objects is suboptimal because kmalloc > can easily fallback into vmalloc under memory pressure and smaller > objects would fragment memory. Therefore replace kvmalloc by a simple > kmalloc.
I think you're wrong here: kvmalloc can failback to vmalloc for size > PAGE_SIZE only
Please take look at mm/util.c::kvmalloc_node()
if (size > PAGE_SIZE) { kmalloc_flags |= __GFP_NOWARN;
if (!(kmalloc_flags & __GFP_RETRY_MAYFAIL)) kmalloc_flags |= __GFP_NORETRY; }
ret = kmalloc_node(size, kmalloc_flags, node);
/* * It doesn't really make sense to fallback to vmalloc for sub page * requests */ if (ret || size <= PAGE_SIZE) return ret;
return __vmalloc_node(size, 1, flags, node, __builtin_return_address(0));
For small objects kvmalloc is not much different just from kmalloc, so the patch is mostly cosmetic.
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