On Thu, Dec 03, 2015 at 05:47:08PM +0000, Catalin Marinas wrote: > On Wed, Dec 02, 2015 at 12:29:04AM +0300, Yury Norov wrote: > > My question. Why aarch64 defines COMPAT_SHMLBA as 0x4000? > > This was done to match the arch/arm value of 4 * 4K. The historical > 32-bit reason for 4 pages is to cope with aliasing VIPT caches (see > https://git.kernel.org/cgit/linux/kernel/git/tglx/history.git/commit?id=4197692eef113eeb8e3e413cc70993a5e667e5b8) > > > If there's > > no specific reason for it, it looks like a bug, and we should > > define it like in arch/arm: > > #define SHMLBA (4 * PAGE_SIZE) /* attach addr a multiple > > of this */ > > I guess you meant COMPAT_SHMLBA.
I citated arm code here. In aarch64 it's COMPAT_SHMLBA, of course. > I'm not sure there is much value in > keeping 4*PAGE_SIZE for larger page sizes but I agree that the current > 16K value doesn't work well with 64K pages. Arnd told there will be a workaround for arm v6 caches. Than this header will not be needed at all. Until that, this is simpliest fix as it doesn't affect userspace. > > -- > Catalin -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
