On Mon, Nov 09, 2015 at 06:36:09PM +0000, Catalin Marinas wrote: > On Mon, Nov 09, 2015 at 04:41:58PM +0900, Joonsoo Kim wrote: > > 2015-11-05 21:17 GMT+09:00 Catalin Marinas <catalin.mari...@arm.com>: > > > 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.
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