> Am 04.01.2021 um 20:52 schrieb Dave Hansen <dave.hansen@xxxxxxxxx>: > > On 1/4/21 11:27 AM, Matthew Wilcox wrote: >>> On Mon, Jan 04, 2021 at 11:19:13AM -0800, Dave Hansen wrote: >>> On 12/21/20 8:30 AM, Liang Li wrote: >>>> --- a/include/linux/page-flags.h >>>> +++ b/include/linux/page-flags.h >>>> @@ -137,6 +137,9 @@ enum pageflags { >>>> #endif >>>> #ifdef CONFIG_64BIT >>>> PG_arch_2, >>>> +#endif >>>> +#ifdef CONFIG_PREZERO_PAGE >>>> + PG_zero, >>>> #endif >>>> __NR_PAGEFLAGS, >>> >>> I don't think this is worth a generic page->flags bit. >>> >>> There's a ton of space in 'struct page' for pages that are in the >>> allocator. Can't we use some of that space? >> >> I was going to object to that too, but I think the entire approach is >> flawed and needs to be thrown out. It just nukes the caches in extremely >> subtle and hard to measure ways, lowering overall system performance. > > Yeah, it certainly can't be the default, but it *is* useful for thing > where we know that there are no cache benefits to zeroing close to where > the memory is allocated. > > The trick is opting into it somehow, either in a process or a VMA. > The patch set is mostly trying to optimize starting a new process. So process/vma doesn‘t really work. I still wonder if using tmpfs/shmem cannot somehow be used to cover the original use case of starting a new vm fast (or rebooting an existing one involving restarting the process).