Re: [PATCH] mm: kfence: allocate kfence_metadata at runtime

[Peng Zhang]

在 2023/7/10 18:37, Alexander Potapenko 写道:
> On Mon, Jul 10, 2023 at 5:27 AM 'Peng Zhang' via kasan-dev
> <kasan-dev@xxxxxxxxxxxxxxxx> wrote:
> > kfence_metadata is currently a static array. For the purpose of
> > allocating scalable __kfence_pool, we first change it to runtime
> > allocation of metadata. Since the size of an object of kfence_metadata
> > is 1160 bytes, we can save at least 72 pages (with default 256 objects)
> > without enabling kfence.
> >
> > Below is the numbers obtained in qemu (with default 256 objects).
> > before: Memory: 8134692K/8388080K available (3668K bss)
> > after: Memory: 8136740K/8388080K available (1620K bss)
> > More than expected, it saves 2MB memory.
>
> Do you have an understanding of where these 2MB come from?
> According to your calculations (which seem valid) the gain should be
> 290K, so either 2MB is irrelevant to your change (then these numbers
> should be omitted), or there's some hidden cost that we do not know
> about.
I don't know why the 2MB memory was saved, but it looks like it has to 
do with the .bss section, maybe removing this array affected the linker?