Re: [PATCH RFC 00/10] KFENCE: A low-overhead sampling-based memory safety error detector

From: Vlastimil Babka
Date: Tue Sep 08 2020 - 15:54:26 EST

On 9/8/20 5:31 PM, Marco Elver wrote:
>> How much memory overhead does this end up having? I know it depends on
>> the object size and so forth. But, could you give some real-world
>> examples of memory consumption? Also, what's the worst case? Say I
>> have a ton of worst-case-sized (32b) slab objects. Will I notice?
> KFENCE objects are limited (default 255). If we exhaust KFENCE's memory
> pool, no more KFENCE allocations will occur.
> Documentation/dev-tools/kfence.rst gives a formula to calculate the
> KFENCE pool size:
> The total memory dedicated to the KFENCE memory pool can be computed as::
> ( #objects + 1 ) * 2 * PAGE_SIZE
> Using the default config, and assuming a page size of 4 KiB, results in
> dedicating 2 MiB to the KFENCE memory pool.
> Does that clarify this point? Or anything else that could help clarify
> this?

Hmm did you observe that with this limit, a long-running system would eventually
converge to KFENCE memory pool being filled with long-aged objects, so there
would be no space to sample new ones?

> Thanks,
> -- Marco