On Mon, Nov 09, 2015 at 04:41:58PM +0900, Joonsoo Kim wrote: > 2015-11-05 21:17 GMT+09:00 Catalin Marinas <[email protected]>: > > On Thu, Nov 05, 2015 at 08:45:08PM +0900, Joonsoo Kim wrote: > >> If it isn't possible, is there another way to reduce memory waste due to > >> increase of dma alignment requirement in arm64? > > > > I first need to see how significant the impact is (especially for > > embedded/mobiles platforms). > > I don't have any ARM64 device. What I have just one report > about slab usage from our developer. > > The report shows slab usage just after android boot is done > in ARM64. > > Total slab usage: 90 MB > kmalloc usage: 25 MB > kmalloc (<=64) usage: 7 MB > > This would be measured without slab_nomerge so there is > a possibility that some usages on kmem_cache is merged > into usage of kmalloc (<=64). > > Anyway, if ARM64 increase L1_CACHE_BYTES to 128, roughly > 7 MB would be wasted. I don't know how this picture is varied > in runtime, but, even boot time overhead, 7 MB looks large to me.
7MB is considerable but I guess it wouldn't be all wasted with L1_CACHE_BYTES == 128, maybe half or slightly over. It would be good to know the other kmalloc caches, maybe up to 256. I don't have an Android filesystem but I just tried to boot Arch (aarch64). Immediately after boot and slab_nomerge, with 128 L1 I get: kmalloc-128: 6624 kmalloc-256: 1488 With L1 64, I get: kmalloc-64: 5760 kmalloc-128: 1152 kmalloc-192: 1155 kmalloc-256: 320 So that's about 1.2MB vs 0.8MB. The ratio is 3:2, though I'm not sure it will stay the same as the slab usage increases. It would be good to get more numbers, we could add a Kconfig option just for specific builds while keeping the default to 128. -- 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/
