On Mon, Apr 29, 2013 at 04:26:41PM +0100, Catalin Marinas wrote: > Steve, Hi Catalin, > > On Mon, Apr 29, 2013 at 03:55:55PM +0100, Steve Capper wrote: > > Under x86, multiple puds can be made to reference the same bank of > > huge pmds provided that they represent a full PUD_SIZE of shared > > huge memory that is aligned to a PUD_SIZE boundary. > > > > The code to share pmds does not require any architecture specific > > knowledge other than the fact that pmds can be indexed, thus can > > be beneficial to some other architectures. > > > > This patch copies the huge pmd sharing (and unsharing) logic from > > x86/ to mm/ and introduces a new config option to activate it: > > CONFIG_ARCH_WANTS_HUGE_PMD_SHARE. > > Just wondering whether more of it could be shared. The following look > pretty close to what you'd write for arm64: > > - huge_pte_alloc() > - huge_pte_offset() (there is a pud_large macro on x86 which checks for > present & huge, we can replace it with just pud_huge in this function > as it already checks for present) > - follow_huge_pud() > - follow_huge_pmd() I did do something like this initially, then reined it back a bit as it placed implicit restrictions on x86 and arm64. If we enable 64K pages on arm64 for instance, we obviate the need to share pmds (pmd_index doesn't exist for 64K pages). So I have a slightly different huge_pte_alloc function to account for this. I would be happy to move more code from x86 to mm though, as my huge_pte_offset and follow_huge_p[mu]d functions are pretty much identical to the x86 ones. This patch, I thought, was the most I could get away with :-). Cheers, -- Steve > > Of course, arch-specific macros like pud_huge, pmd_huge would have to go > in a header file. > > -- > Catalin -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>