On Tue, Sep 29, 2020 at 3:11 PM Marco Elver <elver@xxxxxxxxxx> wrote: > > On Tue, Sep 29, 2020 at 02:42PM +0200, Andrey Konovalov wrote: > [...] > > > + */ > > > + index = (addr - (unsigned long)__kfence_pool) / (PAGE_SIZE * 2) - 1; > > > > Why do we subtract 1 here? We do have the metadata entry reserved for something? > > Above the declaration of __kfence_pool it says: > > * We allocate an even number of pages, as it simplifies calculations to map > * address to metadata indices; effectively, the very first page serves as an > * extended guard page, but otherwise has no special purpose. > > Hopefully that clarifies the `- 1` here. So there are two guard pages at the beginning and only then a page that holds an object?
