Re: [PATCH RFC v2] Randomized slab caches for kmalloc()

[Gong Ruiqi]

On 2023/05/17 6:35, Hyeonggon Yoo wrote:
> [Resending this email after noticing I did not reply-to-all]
> 
> On Fri, May 12, 2023 at 7:11 PM Gong Ruiqi <gongruiqi1@xxxxxxxxxx> wrote:
>>

[...]

> 
>>>> +#ifdef CONFIG_RANDOM_KMALLOC_CACHES
>>>> +# define SLAB_RANDOMSLAB       ((slab_flags_t __force)0x01000000U)
>>>> +#else
>>>> +# define SLAB_RANDOMSLAB       0
>>>> +#endif
> 
> There is already the SLAB_KMALLOC flag that indicates if a cache is a
> kmalloc cache. I think that would be enough for preventing merging
> kmalloc caches?

After digging into the code of slab merging (e.g. slab_unmergeable(),
find_mergeable(), SLAB_NEVER_MERGE, SLAB_MERGE_SAME etc), I haven't
found an existing mechanism that prevents normal kmalloc caches with
SLAB_KMALLOC from being merged with other slab caches. Maybe I missed
something?

While SLAB_RANDOMSLAB, unlike SLAB_KMALLOC, is added into
SLAB_NEVER_MERGE, which explicitly indicates the no-merge policy.